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Geological Sciences Theses and Dissertations Abstracts: 2001-2008

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The Theses and Dissertations Abstracts from 2001 to 2008 are from masters and dissertations completed at the University of Texas at Austin in the field of Geological Sciences. See the Theses and Dissertations Index : 2001-2008 for a more concise listing of authors and titles. Dissertation abstracts published prior to 2001 may be found through Dissertations and Theses: Full Text.


INTEGRATED CORE, WELL LOG, AND SEISMIC INTERPRETATION OF ALBIAN PATCH REEFS IN MAVERICK BASIN, SW TEXAS

Enzo Sener Aconcha, M.S. GeoSci

The University of Texas at Austin, 2008

Supervisor: Charles Kerans

106 pages, 64 references

The Albian Glen Rose Formation has been well known as a shallow shelf carbonate with common patch reef development along the interface between the Comanche Shelf and the Maverick Basin. Stratigraphic analysis of 75 well logs and 7 seismic stratal slices formed the basic data for interpreting the Lower Glen Rose sequence framework and paleogeographic setting. The Lower Glen Rose units record the HST of sequence 6 and all of sequence 7. Patch reefs were found in the TST, near the MFS, and the HST of sequence 7, with three distinct reef levels found throughout units 2-4. Buildups in unit 2 change from transgressive isolated buildups into a flat biostrome during progressive onlap. Unit 3 buildups record a landward shift relative to the biostrome of unit 2, as shown on well logs and are coincident with the sequence 7 MFS. The third and uppermost buildup level is found in unit 4, in the late highstand of sequence 7. This unit shows a distinct seaward shift of the patch reefs, relative to unit 3, consistent with the highstand interpretation.

Detailed examination of facies in the two cores available for study indicates that the patch reefs formed during shoaling of the shelf. These patch reefs are characterized by a low API GR value (<20 GAPInorm) and strong negative seismic amplitudes. Off-reef deposits correlate with a higher, variable gamma-ray response (>20 GAPInorm) and positive seismic amplitudes. The patch reefs are proven hydrocarbon reservoirs with gas potential concentrated in units 2 and 4.

Geomorphometric analysis based on seismic stratal slices of more than 30 buildups from unit 4 determined that these are domal features with a distinct NNW-SSE elongation and steeper SW flanks. Asymmetry of the patch reefs may be the result of NW-directed far-field paleo-currents and NNE-directed, wind-driven paleo-waves. Independently of the size scale, the elongation axis of buildups is 1.5-2.5 times larger than its perpendicular direction. Results imply best reservoir facies in the SW side of the Lower Glen Rose patch reefs.

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IMAGING THE LOWER SLOPE, OFFSHORE NICARAGUA AND COSTA RICA USING A NEW RESIDUAL MIGRATION VELOCITY ANALYSIS TECHNIQUE IN THE SPACE-OFFSET DOMAIN

Imtiaz Ahmed, Ph.D.

The University of Texas at Austin, 2003

Supervisors: Paul L. Stoffa and Kirk D. McIntosh

162 pages, 73 references

There is a dramatic variation in geochemical sediment tracer signal along the Central American volcanic arc. Two contradicting theories, one supporting sediment accretion and the other subduction erosion, have been suggested as possible explanations for these variations. My goal in this dissertation is to use seismic images of the lower slope off Nicaragua and Costa Rica to study the influence of subducting plate structure on sediment dynamics. I am particularly interested in documenting the efficiency of sediment subduction, its along strike variation, and to see if it corresponds with the geochemical anomalies.

Although high quality seismic data was acquired offshore Nicaragua, it remained difficult to image the lower slope in detail with conventional processing techniques. Several characteristics of this geologic environment pose seismic imaging problems: the area is heavily faulted, adjacent reflection boundaries have contrasting dips, and the velocity structure is complex. In this environment the common midpoint gathers do not represent a collection of true common subsurface reflection points. To get a clearer image, I needed to apply pre-stack depth migration (PSDM) techniques. An accurate velocity model is required to get a good PSDM image. Therefore one of the most important aspects of PSDM is velocity analysis.

Over the last few decades, residual migration velocity analysis (RMVA) has been an area of active research. Previous work on RMVA in the depth-offset domain required top down layer stripping migration in order to derive the interval velocities directly, hence making it very computationally intensive. Here I propose a new technique in which for each common image gather (CIG) we first create a table of offset-ray parameters-depth ( x-p-z ) using a local 1D assumption. Then I calculate the residual migration depth corrections in the p-z domain and finally map these depth corrections back to the x-z domain using the x-p-z table. Since I calculate the residual migration depth corrections in the p-z domain, the interval velocities are derived directly by top down residual migration. Hence I do not have to explicitly do the layer stripping migration followed by residual normal moveout to get the interval velocities.

The velocities generated by using the above RMVA technique produce interpretable depth images of the lower slope off Nicaragua and Costa Rica. From these images I interpret partial sediment accretion off Costa Rica and likely total sediment subduction off Nicaragua, and therefore provide a geophysical evidence for the observed geochemical disparity along this margin.

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CENOZOIC STRATIGRAPHIC AND TECTONIC HISTORY OF THE GRENADA AND TOBAGO BASINS AS DETERMINED FROM MARINE SEISMIC DATA, WELLS, AND ONLAND GEOLOGY

Trevor John Aitken, M.S. GeoSci

The University of Texas at Austin, 2005

Supervisor: Paul Mann

This thesis presents an integrated stratigraphic and tectonic evolution of the Grenada and Tobago basins using multi-channel seismic data collected in May, 2004, (BOLIVAR cruise), along with GULFREX seismic data collected by Gulf Oil Company in 1975. These reflection data, combined with UTIG OBS refraction data also collected with the BOLIVAR study in 2004 and with a compilation of previously published, onland geologic data in the southeastern Caribbean, constrain a multi-stage, Cenozoic tectonic history for the southern Lesser Antilles arc and flanking Grenada and Tobago basins. A new tectonic model for the Grenada and Tobago basins is based on three seismic megasequences. The striking similarity in the two basins’ half-graben structure, smooth basement character, deep-marine seismic facies, and similar Paleogene sediment thickness suggest that the two basins formed as a single, Paleogene forearc basin related to the now dormant Aves Ridge. This single forearc basin continued to open through flexural subsidence during the early to middle Eocene probably because of slow rollback of the subducting Atlantic slab. The Grenada and Tobago basins began to be divided during the early to middle Miocene, when the thinned crust of the forearc was inverted as a result of: 1) oblique convergence between the Caribbean plate and the passive margin of South America; and 2) intrusion of the Neogene Lesser Antilles arc. Observed transpressional shortening of the basins decreases from southwest to northeast. Total shortening in the southern Grenada basin varies from 5 km in the southern part of the study area to 1 km in the northern part of the study area. Shortening structures include inverted Paleogene normal faults, folds, and shale diapirism. The late Miocene to Recent period is characterized by divided depositional histories of the Grenada and Tobago basins. The Tobago basin is characterized by a 4-km-thick wedge of Plio-Pleistocene clastic sediments inferred to represent the distal progradation of the proto-Orinoco River. The Grenada basin becomes increasingly isolated from further continental sediment input by uplift of coastal Venezuelan ranges and the Neogene Lesser Antilles volcanic ridge.

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3D SEISMIC SURFACE MULTIPLE ATTENUATION: ALOGRITHMS AND ANALYSIS

Abdulaziz Saleh Alaslani, PhD

Supervisors: Paul L. Stoffa and Mrinal K. Sen

The aim of seismic exploration is to provide a comprehensive description of subsurface geologic structure in terms of its reflectivity function at the boundaries between geological units. Seismic multiples are coherent noise that obscure primary events and considerably degrade the quality of seismic images in the target zones. In spite of the fact that many methods have been designed to suppress multiples, only a limited success has been achieved. I have developed two different approaches to address the problem of seismic multiples. The first approach attempts to suppress multiples in terms of decomposition of the measured seismic wavefields into its upgoing and downgoing waves. The separation process is accomplished by using some statistical characteristics of the data in the plane-wave p domain. The ratio of these two components yields the true reflectivity function free of multiples. Although encouraging results are obtained in the separation process, instability occurs during the wavefield division step. As a result, the effectiveness of this approach is limited. I have also investigated seismic multiples for 3D geology and proposed a new methodology in which 3D multiples are predicted and attenuated successfully. The departure of the predicted multiple arrival times from the observed multiple arrival times explains why demultiple algorithms that assume two-dimensional multiple reflections often fail. In this approach, I employed 3D ray tracing to predict the arrival times of the primary and its multiples in individual shot gathers generated from a three-dimensional reflector. A non-linear optimization method, called Very Fast Simulated Annealing (VFSA) is used to determine geometry of the subsurface reflector in 3D. This is achieved by applying a ray traced normal moveout (NMO) correction to seismic reflections with respect to the zero offset time. Based on the optimized NMO-corrected shot gathers, the autoconvolution of the seismic trace is employed to predict the multiple reflections, which are then scaled and subtracted from the original data. The application of this technique to real data demonstrates that the new method successfully suppresses many surface multiples, and is able to recover several deep primary events. This algorithm is robust and computationally very efficient.

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IMAGING OF R3 PROFILE OF CHICXULUB OFFSHORE SEISMIC DATA USING PRESTACK SPLIT-STIP FOURIER MIGRATION IN THE PLANE WAVE DOMAIN

Ali Mansour Aljadher, MSGeoSci

The University of Texas at Austin, 2008

Supervisor: Paul Stoffa

98 pages, 45 references, 1 table

Sixty-five million years ago, a bolide approximately 10 km in diameter traveling over 20 km/sec collided with earth in the Yucatan Peninsula leaving behind the wide multi-ring Chicxulub crater. Two-dimensional (2D) marine seismic reflection data were acquired in 1996 and 2005 to image the crustal deformation. Radial line R3, a 100 km seismic reflection profile, was processed using a conventional seismic data processing flow (McDonald, MS Thesis, 2006). In this study, line R3 is processed using a different scheme using prestack split-step Fourier migration in the plane wave domain. This new seismic imaging of the R3 data collapses the scattered waves, moves the temporal reflection events to their true structural position in depth and increases the signal to noise ratio. The field shot gathers are contaminated with low-frequency guided waves due to the shallow water column and the hard water bottom offshore Yucatan as well as the Scholte waves propagating along the seafloor interface. A 2D normal derivative operator was applied to remove this coherent noise for NMO corrected data. This multichannel filtering approach attempts to reveal the horizontal or nearly-horizontal reflections while non-horizontal evenets such as groundroll and Scholte waves are attenuated. Before migration of the reflections, the seismic shot gathers were mapped from the offset-time (X-T) domain to the vertical delay time, t, and the horizontal ray parameter, p, or simply t-p domain. In the t-p domain, predictive deconvolution often works better since multiples are periodic and hence easier to remove and this usually gives better results than applying the deconvolution in the original offset-time (X-T) domain. Moreover, groundroll and Scholte waves are mapped to points in the t-p domain and there can then be readily excluded for the imaging, improving the signal to noise ratio of the final depth section. For depth migration, a good velocity model is required to image the data to the correct position and depth. Thus, an optimized velocity model was used for prestack plane wave migration. Prestack depth migration was applied directly on the transformed t-p gathers that are sorted into constant ray parameter sections. Each plane wave component, i.e. constant p value, was imaged separately and prestack-migrated common-image-gathers (CIGs) are collected. They are in the depth and ray parameter z-p domain, at each shot position. The migrated and stacked results are obtained by stacking a selected range or all the traces in each CIG to generate the final image. Residual depth versus p “moveout” is then used to refine the interval velocity of the depth section. The result of this new processing is an improved image in depth of the crater which is important to understanding the actual structural geometry of this large impact event. The improved image can give a greater confidence in both the geologic structure and the velocity model than time migration since the events are now in their true spatial position.

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MULTI-DIMENSIONAL LAND SEISMIC DATA-ACQUISITION TECHNIQUES AND RANDOM SURVEY DESIGN

Engin Alkan, MS. Geo. Sci.

The University of Texas at Austin , 2007

Supervisor : Bob Hardage

This study analyzes different techniques and innovations of three-dimensional seismic data acquisition and survey design. Multi-dimensional (both 2-D and 3-D) survey design requires objective consideration of survey goals, the range of expected Earth responses, crew and equipment accessibility, acquisition costs, instrument capabilities, experimental field conditions, and logistic considerations.

Planning a 3-D survey combines operational and technical issues which, in turn, depend on acquisition and design parameters. Because seismic source effort, crew and equipment availability, and size and shape of the survey affect survey cost, it is necessary to understand how all of these factors individually affect the overall data-acquisition program. The main goals of this thesis are to analyze the effect of receiving station coordinate randomness on different 3-D seismic data-acquisition and survey design characteristics, both operationally and technically, and to ultimately optimize the cost and data quality of seismic surveys.

Many advances have been made in imaging subsurface structures at both shallow and deep target locations through improved seismic data-acquisition and processing techniques in the past two decades. Service companies and oil companies continue to develop new techniques to create better 3-D images with higher resolution and improved signal-to-noise ratio.

A major problem that confronts onshore seismic exploration companies is the effects of the acquisition geometry on recorded data. Receiver and source line spacings, range of offsets, and azimuths, fold variations, and source-generated noise are all important issues to consider, as are culture, topography, and surface conditions.

This thesis consists of two parts: (1) station randomness effects on acquisition and survey parameters, and (2) experimental evaluation of Vibroseis sweep parameters. To perform the latter analysis, field data acquired across Tohonadla field at Bluff, Utah were processed, and data generated with various Vibroseis sweep parameters were compared. These analyses allowed data-acquisition and survey design parameters to be related to the cost of the survey and to data quality.

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PRE-STACK INVERSION FOR POROSITY ESTIMATION FROM SEISMIC DATA IN AN OIL FIELD, EASTERN SAUDI ARABIA

Abdulaziz Mohammad AlMuhaidib, M.S. Geo. Sci.

The University of Texas at Austin , 2008

Supervisor: Mrinal K. Sen

107 pages, 41 references, 2 tables

The main objective of seismic inversion is to obtain earth model parameters from seismic reflection data. In other words, it is the process of determining what physical characteristics of rocks and fluids (i.e., P-impedance, shear impedance, and density) could have produced the seismic record. The aim of this study is to obtain reservoir properties, such as porosity both at the well locations and in the inter-well regions from seismic data and incorporated well logs. The target is a Jurassic carbonate reservoir from an oil field located to the East of Saudi Arabia. The purpose was to investigate the reliability of inferring the elastic properties (Zp, Zs, ρ) from seismic data in this field, and to build a geologic framework for flow simulation for better reservoir production forecasting and management.

The seismic data were processed with special attention to preserving the true reflection amplitudes, and were time migrated before stack. Residual moveout from multiples after NMO, however, is almost horizontal at near offset, and constructively add to the stacked amplitude. Therefore, we applied a pre-stack inversion technique on the seismic data, after careful processing, including removal of residual internal multiples. Such an inversion incorporates all of the offsets to obtain an optimum acoustic impedance model. We also investigated the stability of inverting shear impedance and density in the field of study.

The seismic inversion results were overall very good and stable for P-impedance. The match between borehole log and seismic impedance profiles was excellent for the high-contrast events and variable for the low contrast in acoustic impedance, depending on the location within the field. Inverted shear impedance results were less stable compared to P-Impedance, while density was totally unstable and has not been resolved. In general, areas of poor inversion coincided with the zones of poor quality seismic data.

The borehole log data showed a good impedance-porosity relationship. The Raymer-Hunt-Gardner impedance-porosity empirical relation fits the borehole data very well. Thus, I used the Raymer-Hunt-Gardner relation, with coefficients for this field derived from the log data, to convert inverted acoustic impedance into a porosity model for the field. Based on the new quantitative seismic reservoir characterization, I was able to identify additional areas of potentially good reservoir quality.

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MILANKOVITCH ORBITAL FORCING CONTROLS ON SHALLOW-WATER CARBONATE CYCLICITY AND EARLY DOLOMITIZATION: INSIGHTS FROM THE LOWER CRETACEOUS CUPIDO PLATFORM, NE MEXICO

Younis Khamis Altobi, Ph.D

The University of Texas at Austin , 2007

Supervisor: Randall Marrett

High-resolution sequence stratigraphy coupled with understanding of diagenetic processes within carbonate strata improves our understanding of platform evolution controls, facies models, and reservoir quality. The Cupido platform (Barremian to Aptian) exhibits well developed cyclicity and provides unparalleled outcrops to investigate platform morphology, depositional settings, sequence stratigraphic development, origin of high-frequency cycles, and possible climatic controls on early dolomitization across the shelf.

High-frequency cycles stack into twelve depositional sequences (A-L) that correlate across the platform, which, in turn, build into the highstand part of composite sequence I, two complete composite sequences (II and III), and the transgressive based portion of composite sequence IV. Cupido platform interior cycles show evidence for an allocyclic origin, including (a) symmetric and asymmetric peritidal and subtidal cycles, (b) lateral continuity across facies tracts, and (c) incomplete subtidal cycles.

Spectral analyses of cycle thickness reveal a strong Milankovitch signal when sedimentation rate is assumed constant within cycles and cycles are tuned to orbital precession. High spectral density peaks are present for long and short eccentricity (E) period calculated for the Early Cretaceous times: E1 (264-392 kyr), E2 (89-98 kyr), and E3 (107-126 kyr) . Obliquity component with peaks at period (38-59 kyr ) are also present. Strong correlation of Milankovitch signals across the platform suggests that the lateral continuity of high-frequency cycles was caused by shelf-wide sea-level fluctuations.

Early dolomitization of the highstand lower Cupido deposits (LCu) possibly occurred in modified seawater within subtidal and supratidal zones, both at high-frequency cycle-scale and depositional sequence-scale. Dolomitization patterns appear to be linked to Milankovitch-induced 4 th -order sea-level events. The transgressive portions of depositional sequences are more pervasively or preferentially dolomitized compared to the highstand portions. Thickness and periodicity clusters of completely dolomitized cycles are equivalent to thickness and duration of depositional sequences. The results strengthen arguments for the role of Milankovitch-induced sea-level fluctuations in the development of greenhouse carbonate platforms and its control on early dolomite distribution in specific settings.

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TECTONIC GEOMORPHOLOGY OF THE EASTERN TRINIDAD SHELF; IMPLICATIONS FOR INFLUENCE OF STRUCTURE ON RESERVOIR DISTRIBUTION AND NATURE IN OLDER BASIN FILL

Tricia Grier Alvarez, M.S. GeoSci

The University of Texas at Austin, 2008

Supervisor: Lesli J. Wood

Few deltaic systems in tectonically active areas of the world exhibit more data for detailed study than the Orinoco Delta extending along the hydrocarbon-rich, narrow, eastern shelf of the island of Trinidad. The entire region has undergone tectonic extension, compression and transpression during the late Tertiary and into the Quaternary. Paralic and shelf reservoir sand distribution and geometry have been significantly influenced by both structuring and strong offshore current activity, as well as large forced and unforced sealevel regressions. These sedimentary deposits hold significant shallow gas resources across the region, but the complexity of their distribution and architecture is poorly understood. A large merged 3D seismic survey (~9,000 sq km) was integrated with well penetrations across the modern shelf to examine the influence of structuring on near-modern basin fill depositional morphology and architecture.

Key reflecting horizons were mapped across the area and these document the structural opening of the basin by extension superimposed over ongoing uplift of compressional anticlines. Seismic attributes image reservoir elements such as channels and channel belts, tidally inundated interfluves and interdistributary areas which facilitate analysis of the scale and form of these features as well as enable evaluation of the influence of structure on deposition. Both larger channels (1-2 km wide) and smaller channels (less than 100 meters) show patterns of avulsion and lateral migration and appear to be ubiquitous in some areas of the shelf during lowstand times. The largest major sediment fairway (valley) is long-lived (~ 1.0 million years) and structurally confined by east-west trending anticlinal uplifts, funneling sediments down the axis of the basin. Alternations between surfaces with well defined depositional elements interpreted to be indicative of subaerial conditions, and surfaces devoid of such features which have been interpreted to be submarine in nature suggest large scale fluctuations in the depositional environment over time under the influence of changes in sea level.

Extensional faults, which show a complex pattern of displacement, both spatially and temporally; appear to remain active up to near present day time. Coupled with the apparent long-lived nature of the tectonic uplifts in this region, observations suggest that the structure is controlling sedimentation, as opposed to sedimentation driving deformation. Structure is playing a significant role in accommodation creation and therefore the location of the axis of sediment transport and accumulation throughout the Pleistocene history of the basin. This conclusion would be in keeping with the regional structural history of the basin showing transpression between the east-southeastward moving Caribbean Plate and stationary South American plate, initiated in the early Tertiary and continuing to the present day.

Quantitative data on systems tract architectural elements, including spatial orientation and distribution should significantly improve 3D modeling of these reservoirs and improve understanding of sand distribution and the processes of sediment transfer from proximal sources to shelf staging areas.

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EVALUATION OF RISK ANALYSIS METHODS AND THE APPLICATIONS IN EXPLORATION AND PRODUCTION OF AN OFFSHORE PETROLEUM AND GAS FIELD

Ramiro Alberto Amaya, M.A.

The University of Texas at Austin, 2001

Supervisor: Willem C.J. van Rensburg

The aim of this thesis is to present a comprehensive evaluation of risk analysis tools and their application to the oil and gas industry. Risk analysis and decision tools have been largely applied to financial evaluation and oil and gas exploration projects, but their applications to technical risks have been limited. This work deals with technical risks and technical decisions in the operation and production phases. As the main concern of any business, including the oil industry, is the pay-off from financial investments, cash flow methods are also discussed.

Initially, the decision analysis cycle, as well as risk analysis methods and techniques, are described in detail and are applied in critical decision cases of technical and economic risk projects. The Bureau of Economic Geology provided the decision cases data. The information was taken from a current offshore project located in the Gulf of Mexico.

Probability theories and their applications in operations and exploration cases are discussed. An analysis of probability distributions is done to show how to assess exploration and operation uncertainties.

Conclusions presented are based on decision analysis results, supporting economics, and technical facts. Sensitivity analysis, probabilistic risk analysis, decision trees, and expected value are the tools used to make the best possible decision.

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HIGH-PRESSURE METAMORPHISM IN THE WESTERN LLANO UPLIFT RECORDED BY GARNET-CLINOPYROXENITES IN MASON COUNTY, TEXAS

Susan Denise Anderson, M.S.Geo.Sci.

The University of Texas at Austin, 2001

Supervisor: William D. Carlson

Garnet-clinopyroxenites, such as those exposed in Mason County, Texas, are rare in the Llano Uplift of central Texas and are thus important to interpretation of the region's metamorphic history. Because our understanding of the metamorphic history of the Llano Uplift has improved greatly since the garnet-clinopyroxenites in Mason County were first recognized as high-pressure remnants, a re-evaluation of their significance has become necessary. This study provides evidence of in situ metamorphism of the garnet-clinopyroxenites and re-evaluates previous estimates of pressure-temperature (P-T) conditions during early metamorphism of the western Llano Uplift. These interpretations place constraints on tectonic models currently under development for the southern margin of ancient Laurentia during the Grenville Orogeny.

Mapping of the Purdy Hill locality covered ~2 km2 and revealed for the first time substantial outcrop of retrogressed garnet-clinopyroxenites within the Lost Creek Gneiss. The mafic bodies crop out in elongate, pod-like bodies up to 15 m in length and 10 m in width. The bodies are aligned along two major trends that correlate strongly to the surrounding structures of the Lost Creek Gneiss. The orientations and occurrences of the garnet-clinopyroxenites, and the structural setting, of similar rocks in the eastern Uplift (at smaller scale but better exposed), lead to the conclusion that these rocks have been boudinaged, indicating high-grade deformation. These observations provide evidence that the garnet-clinopyroxenites were metamorphosed in situ, that they and their surrounding rocks experienced the same metamorphic history.

The retrogressed garnet-clinopyroxenites at the Sterling Jordan locality, ~2 km northwest of the Purdy Hill locality, contain the best-preserved primary metamorphic assemblage. Fe-Mg exchange thermometry based on interior compositions of garnet-orthopyroxene pairs and garnet-clinopyroxene pairs yields ~750°C, which represents peak or near-peak metamorphic temperatures. These temperatures are supported by the homogenization of garnet growth zoning profiles, the boudinage seen in the mafic rocks, and anatexis in the surrounding quartzofeldspathic Lost Creek Gneiss. Pressure estimates are based on the Al content in orthopyroxene and are complicated by the inhomogeneous distribution of Al within the orthopyroxene grains, particularly by increases in Al at the orthopyroxene rims toward grain boundaries. Compositional X-ray mapping of the spatial variation of Al in orthopyroxene has proven to be an effective method for analyzing such textural information.

Previous studies estimated peak metamorphic conditions of 8.0 - 11 kbar at an average temperature of 750°C based on inferred equilibrium between orthopyroxene rims and garnet interiors (Wilkerson et al., 1988). Re-evaluation of that study and application of a corrected garnet-orthopyroxene barometer have led in this study to estimates of 15-21 kbar at 750°C, within the eclogite facies, based on equilibrium between garnet and orthopyroxene cores, for the early metamorphism. These new P-T estimates for peak metamorphic conditions of the western Llano Uplift are significantly different from estimates for other localities in the north-central and southeastern uplift, perhaps suggesting important differences in their early metamorphic histories.

Compositional modification of adjacent orthopyroxene and garnet rims, producing an increase in Al at the margins of orthopyroxene, occurred as a result of the continued growth of orthopyroxene at the expense of garnet as the rocks began to re-equilibrate to lower P-T conditions subsequent to peak metamorphism. The resulting rim compositions of garnet, orthopyroxene, and clinopyroxene, which likely do not represent complete re-equilibration, yield 0.3 - 5.4 kbar at an average of 650º C; these conditions represent the amphibolite facies. Although it is also possible that this partial re-equilibration occurred along a late, retrograde portion of the same P- T path that produced peak metamorphism, evidence for hydration during this recrystallization episode suggests that the partial re-equilibration was likely associated with the later, lower-pressure amphibolite-facies metamorphism that occurred across the uplift.

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CONTROLS ON CLASTIC WEDGE AND GROWTH STRATA DEVELOPMENT IN FORELAND BASINS: EXAMPLES FROM CRETACEOUS CORDILLERAN FORELAND BASIN STRATA, USA

Jennifer L. Aschoff, Ph.D.

The University of Texas at Austin, 2008

Supervisor: Ron Steel

179 pages, 149 references, 2 plates

Tectonic signatures such as growth strata, clastic progradation, detrital composition, thickness trends, paleoflow shifts, lithofacies distribution, and vertical stratigraphic stacking patterns provide the basis for a range of tectonic/structural interpretations. Complete understanding of the application and limitations of tectonic signatures is important to maintain consistency and reduce uncertainty of interpretations that use them. This study provides insight into the external controls on two frequently used tectonic signatures in foreland basins: (1) growth strata, and (2) clastic wedge progradation. First, two syntectonic unconformity types are recognized in non-marine, Cenomanian growth strata adjacent to the Sevier thrust-belt in southeastern Nevada, USA. Unconformities with larger angular discordance (>10°, “Traditional Type”) developed when uplift outpaced sediment accumulation. More subtle unconformities with less discordance (2-10°, “Subtle Type”) developed when sediment accumulation nearly kept pace with uplift. Increasing sediment supply with positive net accommodation, allows syntectonic deposits to aggrade above a growing structure, with no change in uplift rate. Hence, sediment supply and regional accommodation impart an important control over growth strata geometries that are often interpreted on the basis of tectonics alone. Identification of unconformity types in growth strata can therefore document additional phases of uplift, particularly for intervals where sediments aggraded above an active structure due to higher sediment supply during regional subsidence, or sea level rise. Second, an anomalous, Campanian clastic wedge is identified in Cordilleran Foreland basin fill, Utah and Colorado. The complex internal architecture, tide-dominated facies and characteristic flat-to-falling shoreline stacking patterns of the wedge reflect rapid progradation of wide (60-80 km), embayed, tide-influenced shorelines; these characteristics distinguish the anomalous wedge from the underlying and overlying clastic wedges in the basin. A high-resolution regional correlation and isopach maps for the anomalous wedge provide evidence that extensive clastic progradation was coeval with both Sevier- and Laramide-style deformation. Stratigraphic relations suggest that development of the anomalous character of Wedge B was due to uplift of a Laramide structure within the foredeep, and possibly enhanced by reduced dynamic subsidence.

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MODELING OF RUNOFF-PRODUCING RAINFALL HYETOGRAPHS IN TEXAS USING L-MOMENT STATISTICS

William Harold Asquith, Ph.D.

The University of Texas at Austin, 2003

Supervisor: John M. Sharp

386 pages, 103 references, 0 plates

Temporal distributions of storm rainfall are known as hyetographs. Design hyetographs are important for cost-effective risk-mitigated ramfall-runoff modeling. The hyetographs considered are known to produce or generate runoff on small watersheds (typically about 50 square kilometers) in Texas. L-moment statistics and the nonparametric median are used to summarize the dimensionless representations of over 1,600 observed hyetograph distributions. A focus is made on storm depths in excess of about 25 mm and durations of 0-12, 12-24, and 24 hours and greater. Statistical distributions are fit to the L-moments of the dimensionless hyetographs including the newly described L-gamma. L-gamma hyetograph models are anticipated to be reliable predictors of expected hyetographs. Finally, a separate permeability-related L-moment application to the popular Carman-Kozeny equation is described.

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RESERVOIR CHARACTERIZATION OF THE MIOCENE STARFAK AND TIGER SHOAL FIELDS, OFFSHORE LOUISIANA THROUGH INTEGRATION OF SEQUENCE STRATIGRAPHY, 3-D SEISMIC, AND WELL-LOG DATA

Adrian Constantin Badescu, Ph.D.

The University of Texas at Austin, 2002

Supervisor: William L. Fisher

Many "mature" Gulf of Mexico (GOM) fields, due to their structurally and stratigraphically complex nature, possess significant remaining resources. Such is the case in the Starfak and Tiger Shoal fields, offshore Louisiana. In these fields, forty hydrocarbon reservoirs occur in a regressive Miocene-age succession that comprises 10 third-order and at least 58 fourth-order sequences. Reservoir-scale heterogeneity is controlled by the nature and distribution of sedimentary facies and is usually below the resolution of current subsurface seismic sampling. Sequence-stratigraphic analysis helps to improve predictions of spatial and temporal reservoir heterogeneity. This study addresses the application of the correlation between petrophysical properties (PP) (e.g., effective porosity and shale volume) and seismic attributes (SA) within a high-frequency sequence stratigraphic framework to identify untapped reservoir compartments in the two offshore Louisiana fields.

Synthetic modeling of the seismic data showed that the vertical resolution of the seismic is approximately 12 ms. The relief on the fourth-order sequence boundary (SB) is below seismic resolution. A new method of mapping fourthorder SBs was developed. This method is based on the ability to image planiform morphology along the SB that can be depicted from a sequence of 4-ms-thick stratal slices. This method was successfully applied in the study area, and showed increased resolution when compared to two other mapping methods (manual tracking and proportional slicing).

Three methods were tested to correlate SA with PP: (1) direct correlation between SAs and PPs through regression analysis, (2) seismic inversion, and (3) probabilistic neural network (PNN). Among the three methods, the PNN proved to be the best technique. Four uncontacted compartments targeting incised-valley sands in genetic sequence 30 were identified upon analyzing the inverted Vshale volume created using PNN method.

Starfak and Tiger Shoal are typical of mature shelf-bound fields in the GOM, with long and sustained production histories. Structural and stratigraphic heterogeneities present opportunities for reserve-growth potential if an improved process for mapping of geologic complexity can be unraveled.

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METHODS COMPARISONS AND SPATIAL ANALYSIS OF FIELD PARAMETER QUANTIFICATION OF UNSATURATED FLOW AT AN EXISTING WASTEWATER INFILTRATION SYSTEM; MINES PARK, GOLDEN, COLORADO

Danielle Margueritte Bailey, M.S. Geo. Sci.

The University of Texas at Austin , 2006

 

Co-Supervisors: John E. McCray and Leon E. Long

Subsurface water reclamation systems (SWRS) in mountain watersheds commonly experience issues of water sustainability, and are generally designed through judgment and experience rather than through rigorous quantitative methods. I have made a detailed vadose-zone characterization of several saturated and unsaturated flow parameters in an excavated trench representative of the size of a typical domestic drainage field at a wastewater reclamation test site (WRTS) at Mines Park, Golden, CO with the objective to improve the pre-design techniques associated with SWRS. Most wastewater infiltration is an unsaturated water flow process; therefore, measurement of soil-hydraulic parameters, especially saturated and unsaturated hydraulic conductivity (K sat and K unsat ), is required. Toward this end, I compared the consistency of estimating or measuring K sat and K unsat through field, laboratory, and empirical methods.

Field data collection included Guelph Permeameter and Tension-disc Infiltrometer measurements in the excavated trench, and Slug Test measurements at nearby monitoring wells. Representative soil samples were collected for in-lab experimentation at the UT Bureau of Economic Geology, including the van Genuchten-Mualem transformations of capillary-pressure curves determined from hanging-column measurements. Additional estimates of K sat and K unsat were determined through nine empirical functions and the Rosetta neural network found within Hydrus-1D software. Spatial variations in K sat and K unsat determined from the various methods are illustrated by curves that plot K sat or K unsat according to location. Statistical analyses demonstrate such a large degree of spatial variability that no single measurement adequately represents the values of these parameters, whether along the excavated trench or between the upper and lower tiers of the trench.

The following main conclusions are offered: (1) spatial variations in K sat and K unsat occur along a trench and with depth, in which K unsat exhibits much larger variability with depth than does K sat ; (2) of the empirical functions, results of the Hazen (1893), Harleman et al. (1963), and Beyer (1964) methods compare most favorably to both field methods (Guelph Permeameter, Tension-disc Infiltrometer), providing data that agree with the field-measured values within a factor of two; (3) the Guelph Permeameter field method is the least time consuming and less complicated, but the most arduous to conduct of all field methods; (4) Rosetta estimates with either sand/silt/clay input or soil classification input data provide K unsat values most similar to the Hanging Column values using the van Genuchten-Mualem relationship ; and (5) a single measurement did not appear to represent the hydraulic properties of an entire area occupied by a typical wastewater infiltration trench. I found variation both horizontally along the length of each tier and vertically between Tier 1 (2 feet below ground surface) and Tier 2 (4 feet bgs). This research advances the use of rigorous quantitative measurements and methods in understanding the design of SWRS.

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GRAIN SIZES OF RECENT SILICICLASTIC DEPOSITS IN WAX LAKE DELTA, LOUISIANA

Elke Baitis, B.S.

The University of Texas at Austin, 2008

Supervisor: David Mohrig

Reconstruction of dominant sand transport conditions within the Wax Lake delta using grain-size distributions in recent delta deposits shows that most sand travels as suspended load through the system. When comparing three different bed elevations within the delta, sand deposits reveal a fining upward trend, which compares favorably with estimates of transport style. Very fine sands associated with full suspension predominate at the highest elevations associated with an island levee. Lower fine sands associated with the onset of significant suspension are found distributed in roughly equal proportions across all bed elevations. Upper fine sands linked to incipient suspension are found at all bed elevations but favor channel bottoms. Medium sands, the coarsest component recovered from sediment samples, are found only in the deep feeder channel of the delta and are interpreted to move as pure bedload. These findings along with observations made during average flow conditions in late May, 2007, which showed little to no sand movement through the channels, suggest that delta surfaces are inactive with regards to sand deposition except during infrequent periods of flooding when most of the sand is transported in suspension.

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OSTEOLOGICAL DESCRIPTION OF AN EMBRYONIC ELEPHANT BIRD (RATITAE: AEPYORNIS) USING HIGH-RESOLUTION X-RAY COMPUTED TOMOGRAPHY, WITH A DISCUSSION OF GROWTH IN AEPYORNIS

Amy Michelle Balanoff, M.S. Geo. Sci.

The University of Texas at Austin, 2003

Supervisor: Timothy Rowe

175 pages, 110 references

Very little is known regarding the embryonic skeleton of the extinct elephant bird, Aepyornis, largely due to our hesitation in breaking open rarely recovered intact eggs of this taxon.High-resolution x-ray computed tomography (HRCT), however, provides a non-destructive method for viewing the internal structures of such eggs.The combination of HRCT and three-dimensional rapid prototyping technology made possible the description and reconstruction of a disarticulated embryonic skeleton of Aepyornispreserved within a complete egg.Skeletal elements digitally retrieved from the egg include: the braincase, palate, rostrum, vertebral column, and both fore- and hindlimbs.The cranial morphology of the embryo is well preserved, however due to the early ontogenetic stage of the specimen, development of the postcranial skeleton is less advanced.Comparisons of morphological characters with other embryonic birds allowed an estimation of the ontogenetic maturity as approximately 80-90% through incubation.This specimen, in conjunction with adult material allocated to Aepyornis, was used to construct a growth trajectory that allows a preliminary comparison of growth between Aepyornis and extant ratites.These comparisons offer new insight into the question of how the world’s largest bird got so big.The data suggest that the growth of Aepyornis proceeded in a manner similar to other ratites with a period of rapid growth early in ontogeny that leveled off after hatching.

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PLIOCENE-QUATERNARY DEFORMATION AND MAGMATISM AT THE SOUTHERN MARGIN OF THE PUNA PLATEAU, ARGENTINE ANDES

by

Austin Kyle Baldwin, M.S.Geo.Sci.

The University of Texas at Austin, 2005

Supervisor: Randall Marrett

New fault data and mapping of volcanic rocks from northwestern Argentina's Cordillera de San Buenaventura, a Pliocene-Quaternary, E-W trending volcanic range at the southern margin of the Puna plateau adjacent to the modern volcanic arc at 27°S, reveal numerous tectonomagmatic characteristics unique in the region. Faults in the Cordillera de San Buenaventura dominantly strike ENE-WSW, with lengths reaching at least 30-40 km.  Fault motion, where measurable, has been normal, commonly with a right-lateral component.  Some faults displace alluvium and dated Plio-Quaternary non-explosive lava domes and flows, intermediate in composition, with throws of 1-100 m, whereas other faults do not affect overlying volcanics.  Previous studies in the surrounding southern Puna have reported Pliocene-Quaternary NNW-SSE extension along N-S to NNE-SSW striking right-slip faults commonly associated with volumetrically-minor mafic monogenetic cinder cones and flows. Explosive eruptions with intermediate compositions have also characterized the southern Puna during the Pliocene-Quaternary. Volcanics erupted during this time period in the Cordillera de San Buenaventura lack both mafic and explosive tendencies.  

The new data, combined with existing data, suggest that the Cordillera de San Buenaventura overlies a shallow magma chamber, which thermally weakened the upper crust and promoted the growth of the observed ENE-WSW striking normal and oblique-slip faults during the Pliocene-Quaternary. The new faults created right-stepping extensional transfers by linking preexisting NNE-SSW striking right-slip faults. Decreased horizontal stress at these transfers facilitated magma ascent from the underlying chamber. Periodic breaches of the magma chamber cupola by slip on faults prevented magmatic fluid accumulation and explosive eruptions. Mafic magma ascending beneath the Cordillera de San Buenaventura pooled in the shallow magma chamber, where it assimilated silica-rich crustal material and differentiated, eventually reaching the surface with an intermediate composition. In surrounding areas, where no shallow magma chamber existed, rising magmas reached the surface with mafic compositions. The high topography of the Cordillera de San Buenaventura may be the combined effect of mechanical doming by the shallow magma chamber, thermal uplift, isostatic elevation of an extensional transfer block, and local accumulation of Plio-Quaternary volcanics.

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HYDROTHERMAL FLUIDS AND CU-AU MINERALIZATION OF THE DEEP GRASBERG PORPHYRY DEPOSIT, PAPUA, INDONESIA

Lorraine Marie Baline, M.S. Geo. Sci.

The University of Texas at Austin , 2007

Supervisor: J. Richard Kyle

The Grasberg porphyry Cu-Au deposit is located in the Ertsberg District in the Central Range of Papua, Indonesia. The Deep Grasberg is the deepest explored part of the Grasberg Igneous Complex (GIC) at elevations between 2450 and 3050 m, more than 1100 m below the pre-mining surface. The deposit is hosted by three quartz-monzonite to diorite units, emplaced approximately 3 Ma: the Dalam, the Main Grasberg Intrusion (MGI), and the Kali.

In the Deep Grasberg, the intrusions contain abundant plagioclase phenocrysts with biotite and hornblende as the dominant mafic minerals. Plagioclase has undergone varying degrees of hydrothermal alteration to sericite. Complete alteration of plagioclase to sericite is common in the Dalam, whereas the Early and Late Kali are significantly less altered. Matrix minerals include potassium feldspar and quartz. Quartz occurs as widespread stockwork veins and also is the dominant mineral in the silicified zone, near the GIC-wallrock contact in the Deep Grasberg. Chalcopyrite, with lesser bornite and covellite are the most abundant economic minerals in the Deep Grasberg and are both vein hosted and disseminated. Bornite is most abundant near the center of the Deep Grasberg, whereas covellite abundance increases toward the periphery.

Hydrothermal fluids, supplied from a cupola at depth, created the Grasberg orebody. Due to its relative proximity to the cupola, the Deep Grasberg records a unique fluid evolution and constrains fluid processes during ore formation.

Some changes in the temperature and composition of the hydrothermal fluids in the Deep Grasberg are recorded in quartz crystals. Textures observed using scanned luminescence of 32 samples of quartz veins from the Dalam, MGI, and Kali reveal a complex vein history in the GIC. Alternating light and dark bands forming concentric growth zone textures record changing conditions during quartz precipitation. Point analyses were unable to detect compositional differences in the quartz bands, but X-ray mapping revealed bright bands had higher Al and Ti contents. Subtle compositional changes in quartz suggest that chemical changes in fluid composition may be responsible for the observed growth zonations. Irregular textures in some quartz crystals suggest a period of quartz dissolution occurred as hydrothermal fluids cooled, followed by the resumption of quartz precipitation.

Fluid inclusion populations from 27 samples from the Dalam, MGI, and Kali reveal that a range of fluid compositions were trapped during quartz precipitation. Five types of fluid inclusions are identified: liquid + vapor, vapor-rich, liquid + vapor + halite, liquid + vapor + multi-daughter crystal, and liquid + vapor + opaque. Liquid + vapor + opaque inclusions are believed to represent a supercritical fluid exsolved from a magma at depth, whereas the coexistence of vapor-rich inclusions and high salinity liquid + vapor + halite and liquid + vapor + multi-daughter crystal inclusions represent two separated phases of this fluid after changes in pressure and temperature caused the hydrothermal fluid system to move from the one-phase to the two-phase field. Homogenization temperatures recorded for liquid + vapor + halite, liquid + vapor + multi-daughter crystal, and vapor-rich inclusions are similar. The lowest homogenization temperatures recorded are about 225 °C, but some inclusions did not homogenize at temperatures as high as 700 °C, the maximum temperature able to be reached on the fluid inclusion stage. Two groups emerge from the data, a set of moderate temperature inclusions and a set of higher temperature inclusions. The moderate temperature inclusions have an average homogenization temperature of 368 °C. The higher temperature inclusions have an average homogenization temperature of >598 °C. Calculated salinities for liquid + vapor + halite and liquid + vapor + multi-daughter crystal inclusions indicate that the separated fluid phase from which these inclusions sourced was very saline, containing about 50 wt.% NaCl equivalent. Fluid inclusions in anhydrite from late-stage veins record a significantly cooler fluid, at approximately 250°C at a salinity near 10 wt.% NaCl equivalent.

Similarity in fluid inclusion compositions, temperatures, textures, and chemical zonations in quartz crystals in the veins in all three intrusive units suggest a common fluid source. It also suggests that similar fluid processes were prevalent during quartz vein development in these intrusive units. In the Deep Grasberg, vein quartz precipitated both directly from a supercritical fluid released from a cupola at depth and from a hydrothermal fluid post-boiling. The narrowing of the GIC at depth may have caused “throttling” of fluids in the Deep Grasberg, resulting in relatively increased pressure in the fractures. Decompression of the fluid was inhibited, and fluid inclusions of liquid + vapor + opaque record the earliest fluids . A decrease in pressure resulted in boiling, creating two fluids: a brine and a vapor. These changes in the hydrothermal fluid account for the variety of fluid inclusion types observed in the Deep Grasberg. Additionally, the repetitive growth zonation patterns in quartz suggests that the hydrothermal fluids were released from a cupola at depth into fractures in pulses during quartz precipitation. Fractures remained open, allowing for quartz growth with successive fluid pulses.

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SEISMIC CHARACTERIZATION OF NATURALLY FRACTURED RESERVOIRS

Reeshidev Bansal, Ph.D.

The University of Texas at Austin , 2007

Supervisor: Mrinal K. Sen

Many hydrocarbon reservoirs have sufficient porosity but low perme¬ability (for example, tight gas sands and coal beds). However, such reservoirs are often naturally fractured. The fracture patterns in these reservoirs can control flow and transport properties, and therefore, play an important role in drilling production wells.

On the scale of seismic wavelengths, closely spaced parallel fractures behave like an anisotropic media, which precludes the response of individual fractures in the seismic data. There are a number of fracture parameters which are needed to fully characterize a fractured reservoir. However, seismic data may reveal only certain fracture parameters and those are fracture orientation, crack density and fracture infill.

Most of the widely used fracture characterization methods such as S-wave splitting analysis or amplitude vs. offset and azimuth (AVOA) analysis fail to render desired results in laterally varying media. I have conducted a systematic study of the response of fractured reservoirs with laterally varying elastic and fracture properties, and I have developed a scheme to invert for the fracture parameters.

I have implemented a 3D finite-difference method to generate multicom-ponent synthetic seismic data in general anisotropic media. I applied the finite-difference algorithm in both Standard and Rotated Staggered grids. Stan¬dard Staggered grid is used for media having symmetry up to orthorhombic (isotropic, transversely isotropic, and orthorhombic), whereas Rotated Stag¬gered grid is implemented for monoclinic and triclinic media. I have also developed an efficient and accurate ray-bending algorithm to compute seismic traveltimes in 3D anisotropic media.

AVOA analysis is equivalent to the first-order Born approximation. However, AVOA analysis can be applied only in a laterally uniform medium, whereas the Born-approximation does not pose any restriction on the subsur¬face structure. I have developed an inversion scheme based on a ray-Born approximation to invert for the fracture parameters. Best results are achieved when both vertical and horizontal components of the seismic data are inverted simultaneously. I have also developed an efficient positivity constraint which forbids the inverted fracture parameters to be negative in value. I have im¬plemented the inversion scheme in the frequency domain and I show, using various numerical examples, that all frequency samples up to the Nyquist are not required to achieve desired inversion results.

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THE EFFECTS OF NUTRIENT-BEARING MINERALS ON HYDROCARBON BIODEGRADATION

Joey Jacqualin Barker, M.S. GeoSci

The University of Texas at Austin, 2004

Supervisor: Philip C. Bennett

119 pages, 143 references

In recent decades researchers have found that native microbial communities are capable of degrading numerous environmental contaminants into more benign compounds.  The ability of a microbial consortia to effectively slow the spread of contamination in an aquifer can be limited by the availability of the nutrients needed for metabolism and reproduction. Previous investigations into microbial colonization patterns indicate that microbes may be gaining the necessary nutrients from mineral grains in an aquifer.

The purpose of this study was to determine the effects of mineral chemistry on anaerobic hydrocarbon biodegradation in a nutrient-limited system. These laboratory experiments were conducted using microcosms constructed of native sediment and groundwater from the Bemidji, Minnesota U.S. Geological Survey Toxics Research Site, and minerals containing trace amounts of nutrients. Some microcosms had nutrients added in solution, instead of in mineral form. In the first trial experiment, the contamination of the sterile control with chloroform was found to have contaminated the microbes in the live microcosms during the sampling procedure. New microcosms were constructed for a second trial, and it was found that temperature fluctuations occurring during the sampling procedure affected the ability of the microbes to degrade the hydrocarbons.  Once a steady temperature was maintained the experiments were able to proceed.

The results of the third trial suggest that mineral chemistry does affect hydrocarbon biodegradation rate.  The addition of ferric iron, in both mineral and solution form, had the greatest individual effect on increasing biodegradation.  Phosphorus and nitrogen also increased biodegradation.  However, the combination of phosphorus and iron in the same mineral had the greatest effect on increasing biodegradation of toluene.

Trace amounts of nutrients in minerals {\em do} affect microbial toluene degradation.  Additionally, the nutrient content of the minerals can provide information about the nutrients which are limiting the system.  Degradation rates are controlled in part by small-scale variations in aquifer mineralogy and permeability.  These variations affect which microbial populations are dominant, the concentration of contaminants and the availability of nutrients. These factors affect the biodegradation rate of contaminants. Providing minerals that contain the most limiting nutrients to a microbial community can improve intrinsic bioremediation and limit the spread of hydrocarbons in the groundwater.

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THE SENSITIVITY OF LAND SURFACE MODEL SIMULATIONS TO BIAS CORRECTION OF THE EUROPEAN CENTRE FOR MEDIUM-RANGE WEATHER FORECASTS REANALYSIS

Aaron Andrew Berg, M.S. Geol. Sci.

The University of Texas at Austin, 2001

Supervisors: James S. Famiglietti, and Clark R. Wilson

After sea surface temperatures, the most important boundary condition for the prediction of climate at the seasonal-to-interannual timeframe is the soil wetness state. Unfortunately, large-scale soil moisture observations are not available, and must therefore be provided through a modeling/data-assimilation approach. Modeling the initial moisture status of a soil requires a comprehensive list of surface water and energy fluxes at consistent temporal and spatial scales. Such data are not presently available except in weather reanalysis products. However, reanalysis products are often biased due to errors in the weather forecast model. In the present study, an attempt to minimize errors to model predictions of the initial soil moisture status is realized through a bias reduction scheme to the reanalysis forcing. The bias reduction scheme uses difference and ratio-based corrections to the reanalysis with global observational datasets. The corrected and original forcing was used to simulate water and energy fluxes within a land surface modeling framework. Output from the land surface model was compared with observations to assess the impact of the bias correction on simulation accuracy. Results of this study demonstrate the implementation of a bias reduction scheme reduces errors in the simulation of runoff, soil moisture, and snow depth. Accordingly, the initializations produced should also be closer to actual surface conditions, and therefore more useful to the climate modeling community. Modelers using reanalysis products for driving land surface models especially for the establishment of initial conditions are cautioned on this approach, and advised to consider a bias reduction strategy.

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STRAIN RATES AND CONSTRAINTS ON CHEMICAL HOMOGENEITY AND LENGTH SCALES OF EQUILIBRATION DURING ALPINE METAMORPHISM AT PASSO DEL SOLE, CENTRAL SWISS ALPS

Christopher Andrew Berg, Ph.D.

The University of Texas at Austin , 2007

Supervisor: William Carlson

Garnet-bearing gneisses from the vicinity of Passo del Sole, Central Swiss Alps, have undergone a complex history of metamorphism and deformation that has imbued them with unique compositional and textural variations. Complex, concentric zoning patterns in garnet may be correlated between porphyroblasts on the scale of a hand sample; however, the character of the Ca, Mn, and Y zoning patterns in garnet vary within single layers on the meter-scale. Within a hand sample, individual compositional zones can be correlated from crystal to crystal on the basis of chemical similarities (e.g., intricate yet identical variations in calcium concentration; equivalent manganese concentrations at zone boundaries) and textural similarities (e.g., initiation of inclusion-trail curvature). These relationships allow the identification of individual compositional zones as time markers during garnet growth.

Detailed examination of garnet growth zoning patterns, in combination with measurements of inclusion-trail curvature within garnet porphyroblasts and detailed thermodynamic models of the garnet growth history in selected samples, together with an assumed heating rate associated with Alpine metamorphism, allows quantification of strain-rates during prograde amphibolite-facies metamorphism along the northern margin of the Lucomagno nappe. Constraints on the nucleation and timing of garnet growth and garnet growth rate mechanisms permit further insight into the relationship between strain-rate and metamorphism at Passo del Sole than had previously been possible with this method: variations in strain-rate magnitude of over a factor of ten (10 -14 – 10 -13 s -1 ) are observed, which correlate with core-to-rim changes in compositional zoning.

The source of the incredible diversity of compositional zoning patterns in garnet is hypothesized to be open-system infiltration of ephemeral, channelized Ca- or Mn-rich fluids derived from magmatic sources or equilibrated with metamorphic rocks deeper in the section. Stages of garnet growth associated with increased strain rates are also correlated with the high-Ca or high-Mn zones within the garnet porphyroblasts, presumably as the result of strain softening associated with the passage of these fluids. In-situ oxygen isotope analysis using SIMS demonstrates that the changes in major-element zoning patterns correlate with small shifts in the isotopic composition of garnet.

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SEQUENCE STRATIGRAPHY AND DEPOSITIONAL HISTORY OF THE UPPER CAÑON DEL TULE, LAS IMAGENES, AND LOWER CERRO GRANDE FORMATIONS, CENTRAL PARRAS BASIN, NORTHEASTERN MEXICO

Juan Clemente Bermúdez Santana, Ph. D.

The University of Texas at Austin, 2003

Supervisor: Richard T. Buffler

210 pages, 100 references, 20 plates

This dissertation describes the results of a field-oriented sequence stratigraphic study of a 900-m-thick Maastrichtian interval in the middle portion of the Upper Cretaceous Difunta Group. Basic analysis of rock features and their stratigraphic arrangement were used to subdivide the interval into transgressive (TST), highstand (HST), and falling stage (FSST) systems tracts and to recognize their bounding surfaces.

The progradational offshore to lower shoreface highstand (HST) deposits of the upper Cañón del Tule Formation and the underlying transgressive (TST) deposits, contain gastropods and bivalves common in shallow marine Lower Maastrichtian strata. However, the occurrence of the ammonite Coahuilites sheltoni restricts these rocks to the lower Upper Maastrichtian.

In the Late Maastrichtian, the final stage of shallow marine sedimentation of the upper Cañón del Tule Formation was characterized by an abrupt change. Accommodation space was reduced in proximal settings, and the shoreline and coarse-grained facies belts migrated basinward in response to a relative sea level fall (forced regression). Wave scouring of the seafloor, and rip and longshore currents produced a regionally extended forced regression surface and sequence boundary characterized by meter-scale gutter casts.

The FSST upper shoreface to foreshore deposits of the uppermost Cañón del Tule Formation include a ridge-forming sandstone of variable thickness. Its internal stratigraphic architecture suggests that high-frequency pulses of sea level risings punctuated the forced regression. During this process, thick, aggradational red deposits of the lower Las Imágenes Formation (FSST) accumulated over the adjacent coastal plain until an intermittent marine transgression began. T he initial transgressive pulses occurred across a rapidly subsiding coastal plain, which favored the development of charophytes in fresh and brackish water environments, associated with benthonic foraminifers, ostracods, oysters, Ophiomorpha and Thalassinoides . Mixed-load probably meandering rivers drained the coastal plain bounded by lagoons and extensive shoreface and offshore environments for this part of the Late Maastrichtian Gulf Coast of México. After this stage of intermittent marine transgression, shallow seas and transgressive (TST) deposits of the lower Cerro Grande Formation covered the region.

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STUDIES ON POST-NATAL VARIATION AND VARIABILITY IN THE VERTEBRATE SKELETON AND ITS PALEONTOLOGICAL IMPLICATIONS

Gaberiel Stephen Bever, Ph.D.

The University of Texas at Austin, 2006

Supervisor: Christopher J. Bell

Developmental biology combined with phylogenetic systematics is broadening our perspectives on the role of intraspecific variation in morphology. These perspectives include conceptualizing variability as a reflection of the evolutionary history of the underlying developmental pathways. I conducted a series of studies explicitly addressing the implications that intraspecific variation and variability have for the description, analysis, and interpretation of fossil vertebrates.

The first chapter examines variation in the anuran ilium as a test case for the potential problems that intraspecific variation has on our perceptions of the fossil record. Results indicate that no distinctive morphologies in the ilium of extant North American Bufo are known that support species-level identifications. These observations indicate that our current understanding of the evolutionary history of many extinct and extant taxa based on the fossil record is highly influenced by our assumptions regarding the distribution of taxa through space and time. Restricting identifications to higher taxonomic levels that can be supported with apomorphies helps to avoid circularity if fossil identifications are used subsequently in analyses offaunal dynamics.

Chapters 3 and 4 examine the nature of intrapopulational variation in the crania of two extant turtles, Sternolherus odoratus and Pseudemys texana. Results indicate that the number of variable characters- and the levels at which they vary- are surprisingly high considering the conservative nature of both the taxonomic sample and the pool of examined characters. Variability can be unevenly distributed within and between age groups, sexes, and modular partitions of the skull. Complex patterns of post-natal ossification are a major source of intraspecific variation.

The final chapter examines the potential implications that polymorphic characters have for the phylogenetic assessment of fossils and the potential for objectively estimating variation in extinct lineages. Results indicate that polymorphic characters can significantly affect phylogenetic hypotheses that include fossils. However, a modem view of variability, combined with increasing data on variation in both extant and extinct lineages, not only provides an objective means to estimate variation in fossil specimens but represents a largely untapped source of phylogenetic information that is a potentially important research trajectory in evolutionary morphology.

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THE ORIGIN AND EVOLUTION OF THE GRAN DESIERTO SAND SEA

Carrie Ann Beveridge, M.S.

University of Texas at Austin, 2004

Supervisor: Kocurek, Gary

The Gran Desierto Sand Sea of Sonora, Mexico is located on the northeastern shore of the Gulf of California, east of the Colorado River Delta. The modern sand sea covers an area of 5700 km² and is the largest active dunefield in North America. The Gran Desierto is well-suited for investigation into the timing and nature of aeolian activity and regional climate change as it contains multiple dune geomorphic elements that compose the complex pattern observed today. Individual generations of dune geomorphic features are identified and ‘backstripped’ through the utilization of several techniques. Methods include remote sensing and statistical analysis of physical parameters of the dune geomorphic forms, as well as absolute age determination of individual generations through optically stimulated luminescence (OSL) age dating techniques. Individual generations of dune geomorphic features are digitized from a Landsat 7 multispectral composite. Crestline lengths, spacings and orientations are statistically analyzed in order to identify distinct trends among individual groups of dunes. These groups are then compared with dune geomorphic features visible on a satellite image overlain on a vertically exaggerated digital elevation model. OSL ages are utilized to determine individual generations within each dune group. These generations are then correlated with global climatic events, and associated variability in predominant wind regimes. Aeolian units sit on top of alluvium that is sourced from distal alluvial fans of Tertiary granitic outcrops, and from fluvial sediments deposited as the ancient Colorado River avulsed westward across the region throughout the Pleistocene. Alluvium is dated from ~87 ka to ~26 ka. Six generations of dune geomorphic features ranging in age from 26,000 years to modern are identified. Based on gross bedform normal transport, wind regimes are reconstructed since LGM. From ~26 ka to ~12 ka, winds shifted from N and NNW to NW and S. From ~12 ka to ~ 10 ka, winds shifted to SE dominant with a subordinate NW component. From ~10 ka to ~6 ka, NW winds became dominant over the south winds and more northerly. Modern conditions were reached by (at latest) ~6 ka, with the exception of enhanced ENSO cycles ~2.4-2.8 ka.

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ANATOMY AND PHYLOGENY OF XENOSAURUS AND ITS EXTINCT RELATIVES

Bhart-Anjan Singh Bhullar, M.S.Geo.Sci.

The University of Texas at Austin, 2008

Supervisor: Christopher J. Bell

Xenosaurus is an enigmatic clade of Mexican and Central American lizards distinguished by knob-like scalation and flattening of the head and body associated with living in cracks within cliff faces. The position of Xenosaurus within the larger clade Anguimorpha is difficult to determine due to a combination of primitive features and unique, highly modified anatomy that obscures useful characters. Evidently, the phylogenetic stem of Xenosaurus represents a long independent history of evolution. Fortunately, several fossil taxa exist that can elucidate this history. These taxa include the extinct Exostinus lancensis (Cretaceous), Exostinus serratus (Oligocene), and Restes rugosus (Paleocene), the latter two known from substantial but inadequately described cranial material. Using osteological and alcohol-preserved specimens, fossils, and high-resolution x-ray CT scans thereof, I attempted to reconstruct the relationships of the three fossil taxa and the six extant species of Xenosaurus that are available in U.S. collections.

An exhaustive CT-data-based description of the skull elements of Exostinus serratus yielded several character states suggesting that this taxon is the immediate sister to Xenosaurus, as well as a host of unusual autapomorphic features. Special care was taken during the description to account for soft anatomical correlates of osteology.

Despite the considerable phylogenetic importance of Xenosaurus and its stem, this is the first phylogenetic analysis of the group. An exhaustive search of the skeleton, including osteoderms embedded in the skin visualized using CT scanning, yielded 274 new characters, substantially more than have been used previously in gross anatomy-based analyses of such a restricted group of reptiles. The great number of characters is largely the result of the availability of disarticulated skeletal material; CT scans showing internal bone structure and bones embedded in the skin; and attention to subtle anatomical differences whose validity could be assessed in terms of intraspecies variation because of the availability of large sample sizes for certain taxa.

My results suggested that Restes rugosus is sister to the other xenosaurs, resolving a polytomy with other Anguimorpha recovered by previous work. Exostinus lancensis is problematic in that it may represent several distinct taxa, but it was recovered as sister to E. serratus + Xenosaurus, making Exostinus paraphyletic. Exostinus serratus emerged as sister to Xenosaurus. Xenosaurus comprises a northern clade consisting of X. newmanorum and X. platyceps; the remaining taxa are united as a southern clade. Within the southern clade, X. agrenon and X. rectocollaris are sister to X. grandis and X. rackhami. North-south splits within Xenosauridae mirror those of several other lizard clades and may be the legacy of the equatorial contraction of early Tertiary tropical forests.

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TIDAL SIGNATURES IN SAND PRONE, TECTONICALLY GENERATED JURASSIC STRAITS, SCOTLAND

Stuart Blackwood, MSGeoSci

The University of Texas at Austin, 2006

Supervisor: Ron J. Steel

The Mid-Jurassic Bearreraig Formation is superbly well exposed on the Isles of Skye and Raasay in NW Scotland. In southern Skye the Bearreraig displays a spectacular, cyclical hierarchy of sand rich, tide-generated bedforms:

1. Upward thickening to thinning compound and compound-compound trough cross-sets (3D dunes) up to 2.5m thick

2. Compound trough cross-sets (3D dunes) up to 10m thick

3. Upward thinning, simple and compound planer cross-sets (2D dunes) up to 50cm thick

Tectonically-generated sequences (up to 140m thick) consisting of these three dune types can be recognized within the formation.

Sedimentation occurred in NNE-SSW-aligned, North Skye/Raasay and South Skye half-grabens, defined by Aalenian-Bajocian faulting associated with the initial opening of the North Atlantic . SSW oriented (S. Skye) and NNE oriented (N. Skye/Raasay) fault-parallel paleocurrent directions (indicative of basin separation) suggest that the faults were active and had enough topographic expression to enhance the tidal regime in these very narrow, block-tilted zones.

Previous depositional interpretation of the Bearreraig is one of alternating tide-dominated deltaic and macro-tidal estuarine cycles with high-frequency regressions and transgressions. Facies cropping out at Trotternish in N. Skye, and Raasay display trends consistent with this regional interpretation. However, in southern Skye the overall thickness of the cross-stratified succession, anomalously large size of the bedforms (implying relatively deep water), intensely sand-rich character of the succession, together with the high bioclastic content of broken shell debris is indicative of a more complex, higher-energy depositional environment. The character and scale of the bedforms, and the absence of pro-delta, lagoonal or delta-plain deposits suggests a narrow seaway or tidal strait generated by active tilting of narrow fault blocks.

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FIELD EXPERIMENTS FOR FRACTURE CHARACTERIZATION: STUDIES OF SEISMIC ANISOTROPY AND TRACER IMAGING WITH GPR

Nedra Danielle Bonal, Ph.D.

The University of Texas at Austin , 2007

Supervisor: Clark R. Wilson

Knowledge of fracture orientation and density is significant for reservoir and aquifer characterization. In this study, field experiments are designed to estimate fracture parameters in situ from seismic and GPR (radar) data. The seismic experiment estimates parameters of orientation, density, and filling material. The GPR experiment estimates channel flow geometry and aperture.

In the seismic study, lines of 2D data are acquired in a vertically fractured limestone at three different azimuths to look for differences in seismic velocities. A sledgehammer, vertical source and a multicomponent, Vibroseis source are used with multicomponent receivers. Acquisition parameters of frequency, receiver spacing and source-to-receiver offset are varied. The entire suite of seismic body waves and Rayleigh waves is analyzed to characterize the subsurface. Alford rotations are used to determine fracture orientation and demonstrate good results when geophone orientation is taken into account. Results indicate that seismic anisotropy is caused by regional faulting. Aaverage fracture density of less than 5% and water table depth estimates are consistent with field observations. Groundwater flow direction has been observed by others to cross the fault trend and is subparallel to a secondary fracture set. In this study, seismic anisotropy appears unrelated to this secondary fracture set. Vp/Vs and Poisson's ratio values indicate a dolomite lithology. Sledgehammer and Vibroseis data provide consistent results.

In the GPR experiment, reflection profiles are acquired through common-offset profiling perpendicular to the dominant flow direction. High frequency waves are used to delineate fluid flow paths through a subhorizontal fracture and observe tracer channeling. Channeling of flow is expected to control solute transport. Changes in radar signal are quantitatively associated with changes in fracture filling material from an innovative method using correlation coefficients. Mapping these changes throughout the survey area reveals the geometry of the flow path of each injected liquid. The tracer is found to be concentrated in the center of the survey area where fracture apertures are large. This demonstrates that spatial variations in concentration are controlled by fluid channel geometry.

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DEVELOPMENT OF A PARALLEL RIVER TRANSPORT ALGORITHM AND APPLICATIONS TO CLIMATE STUDIES

Marcia Lynne Branstetter, PhD

The University of Texas at Austin, 2001

Supervisor: James S. Famiglietti

The global hydrologic cycle plays a central role in the interactive functioning of the Earth’s climate system. The theme of this study is land-oceanatmosphere interaction. Continental runoff has a notable effect on the global hydrologic cycle, both directly as freshwater forcing on the oceans and indirectly through effects on global patterns of precipitation and coincident feedbacks to continental runoff. To demonstrate this, a series of three projects involving both observations and modeling were completed.

The first phase involved the development of a parallel river transport model to deliver runoff from the land surface to the oceans at the appropriate location and time. Within each watershed, the river routing algorithm used cellto- cell routing by considering the mass balance of surface inflows and outflows. This river transport model was then incorporated into a climate system model.

The second and third phases involved the use of a climate system model to investigate the effect of continental runoff. To test the sensitivity of the oceans to freshwater input from runoff, in the second phase, a number of 70-year simulations were conducted, using the ocean and ice components of a highresolution climate model with observed runoff and modeled atmospheric forcing. A half-degree observed runoff data set, consisting of both annual and monthly averages, was used for this forcing. Differences in sea surface temperature and salinity between simulations with and without the addition of runoff were found in the Arctic, Tropical Atlantic, and North Atlantic Oceans. The differences were especially pronounced in the North Atlantic. By affecting sea surface temperatures and salinity, the addition of freshwater from river runoff led to a reduction in North Atlantic Deep Water formation and a corresponding slowdown of heat transport.

The third phase used a fully coupled land-ocean-atmosphere-ice model plus the river transport model from the first phase. Two 200-year simulations were conducted, with and without the river component. The simulation with rivers had reduced oceanic meridional heat transport. Reduced convective rainfall and runoff during January in the simulation with rivers indicated a feedback from the continental runoff flux into the oceans back to the land surface.

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DELINEATING CONTRIBUTING AREAS FOR KARST SPRINGS USING NEXRAD DATA AND CROSS-CORRELATION ANALYSIS

Trevor Jones Budge, PhD

The University of Texas at Austin, 2008

Supervisor: John M. Sharp, Jr

189 pages, 88 references, 2 tables

The use of cross-correlation analysis on spring discharge and precipitation data in karst aquifer basins has been used for many years to develop a conceptual understanding of an aquifer and estimate aquifer properties. However, to this point, the application of these processes has relied on gaged precipitation at discrete locations. The use of spatially varying precipitation data and cross-correlation analysis provides a means of spatially characterizing recharge locations on a karst aquifer. NEXRAD provides a spatial estimate of precipitation based by combining reflectivity measurements from radar stations and traditional precipitation gages. This study combines NEXRAD precipitation data with spring discharge data to develop maps of contributing areas for two karst springs in Central Texas. By calculating the cross-correlation of each NEXRAD measurement to spring flow data for the same period of time a map showing the locations hydraulically connected to the spring can be developed. Both numerical experiments and field applications were conducted as part of the study. The numerical experiments conducted by Padilla and Pulido-Bosch are revisited using the numerical groundwater model MODFLOW. This allowed the introduction of spatially varying parameters into the model. The results show that spatially varying parameters can be inferred based on the results cross-correlation of spatially varying precipitation with respect to a single spring discharge location. Also, contributing area maps are prepared for both Barton Springs and Jacob’s Well. Barton Springs has a precise estimate of the recharge area. The current map of the recharge area and the NEXRAD derived map show good agreement with the cross-correlation results. Conversely, Jacob’s Well has not been sufficiently studied to delineate a contributing area map. This study provides an preliminary estimate of the area contributing to flow at Jacob’s Well. Finally, the development of these maps can also be applied to the construction of regional groundwater models. An application of this methodology with the groundwater availability model for the Barton Springs portion of the Edward’s aquifer is introduced. The application of spatial cross-correlation analysis to constrain recharge in the model showed a reduction in the objective function with respect to discharge at Barton Springs of 15%.

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ESTIMATING BIOZONE HYDRAULIC CONDUCTIVITY IN WASTEWATER SOIL ABSORPTION SYSTEMS USING INVERSE NUMERICAL MODELING

Johnathan R. Bumgarner, M.S. Geo. Sci.

The University of Texas at Austin, 2005

Supervisors: John E. McCray and Bridget R. Scanlon

Wastewater soil absorption systems (WSAS) are commonly used in the United States to treat domestic wastewater prior. Soil clogging occurs at the infiltrative surface of WSAS due to the accumulation of suspended solids, organic matter, and chemical precipitates during continued wastewater infiltration. This low permeability zone is referred to as a biozone. A certain degree of clogging enhances wastewater treatment due to increased residence times and nutrient use by organisms. Conversely, too much clogging can cause WSAS to backup and ultimately fail. As such, determining a generalized set of biozone hydraulic parameters and whether those parameters vary in different types of WSAS or for different loading rates are integral to proper WSAS design and installation.

Because the system is unsaturated and the biozone-soil interface behaves like a capillary barrier, simply estimating infiltration using Darcy’s equation, which assumes saturation, may not be appropriate. Therefore, inverse modeling was conducted using the HYDRUS-1D multi-phase modeling software. Input data for the model simulations, which include infiltration rates and soil hydraulic parameters, were determined at a test site at Colorado School of Mines (CSM). The test site includes ten each of three different types of WSAS – bundle, chamber, and gravel – for a total of 30 test cells. Half of the test cells received a loading rate of 4 cm/day, while the other half received 8 cm/day for one year. Both of these loading rates are higher than the Jefferson County, CO, recommended loading rate of 2 cm/day. Use of different loading rates is an attempt to simulate systems of different ages because the biozone becomes less permeable as the WSAS ages. Constant head infiltration tests were conducted by researchers at CSM in each of the test cells at the time of site installation to calculate the saturated hydraulic conductivity (K s) of the soil, and falling head infiltration tests were conducted after 12 months to calculate the biozone K s.

HYDRUS-1D was used to establish the retention function parameters and K s for biozones at Mines Park via inverse modeling. Of the parameters estimated by HYDRUS-1D inverse simulations, K s has the greatest impact on the falling head test model results when the system is near saturation (volumetric water content > 90%). According to the simulation results, the biozone is near saturation and, therefore, K s weighted most heavily in the data analysis. Results of the modeling process indicate that there are no significant differences (α=0.10) between the mean K s of cells of different types or loading rates (total mean K s = 2.12 cm/day ± 0.78). On the other hand, there is a significant difference (α=0.10) between the mean K s calculated by HYDRUS-1D (2.12 cm/day ± 0.78) and that calculated by Darcy’s equation (3.02 cm/day ± 0.89), but that difference is physically inconsequential. Ponding did not occur in any of the WSAS simulations with 2 cm/day loading rates. Finally, an acceptable set of biozone hydraulic parameters for each of the test cells is established by the modeling process for use at the CSM outdoor laboratory. These parameters will be used to constrain transport in future investigations at the site including contaminant attenuation and loading rate studies.

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MID-PLEISTOCENE TO PRESENT STRATIGRAPHIC RESPONSES IN A TECTONICALLY- DRIVEN DEPOSITIONAL SETTING: EEL RIVER BASIN, NORTHERN CALIFORNIA

Robert Lawrence Burger, Ph.D.

The University of Texas at Austin, 2002

Supervisors: William E. Galloway, Craig S. Fulthorpe, and James A. Austin, Jr.

The Eel River Basin of northern California is an actively deforming forearc basin, affected today by Gorda-North America Plate convergence, northward migration of the Mendocino Triple Junction, glacioeustatic sea-level fluctuations that periodically exposed the continental shelf, and high rates of sediment input. A high-resolution multichannel seismic reflection survey of the shelf and upper slope has been conducted as part of the Office of Naval Research STRATAFORM initiative, with the goal of understanding processes affecting sediment dispersal and preservation in this complex continental margin setting.

Interpretations of the seismic images indicate that, although tectonism strongly overprints preserved sequence morphologies, glacioeustacy is of primary importance in the distribution and preservation of sediments along this margin. On the shelf, stacked sequences dominated by interpreted highstand marine sediment are separated by prominent ravinement surfaces formed during sea-level transgressions. Folding and faulting locally modify sequence morphologies. At the south end of the seismic grid, localized uplift attributed to Mendocino Triple Junction encroachment overrides the glacioeustatic stacking pattern dominant over the rest of the shelf, inducing shelf incision and preferential preservation of vertically stacked channel-fills. An abrupt shift in shelf sequence morphology ~500 ka suggests that the triple junction began to affect the southern basin at that time, by decreasing accommodation space marginwide.

On the adjacent slope, effects of tectonism and glacioeustacy can also be discerned. In the south, the Humboldt Slide is identified as a long-lived masswasting feature, likely triggered by triple junction-related uplift and associated seismicity ~450-500 ka. However, a cyclical succession of contrasting lithologies is also apparent in the deformed slide sequences, which I attribute to glacioeustatic cyclicity. To the north, effects of regional tectonism are less apparent: the slope is dominated by channels and gullies that incise and infill due to presumed glacioeustatically-induced variations in slope sediment supply. However, shifts in lateral channel distributions through time may be an indication of marginal uplift.

Although ground truth is needed to test the broad stratigraphic development models proposed by this study, seismic images of the Eel River Basin confirm the complex interplay of processes influencing sediment deposition and preservation in this active margin setting.

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A GENERAL TRANSFORM FOR REVERSIBLE SEISMIC DATA PROCESSING BY NONSTATIONARY FILTERING

William Andrew Burnett, M.S. Geo. Sci.

The University of Texas at Austin , 2007

Supervisor: Robert J. Ferguson

I use the nonstationary equivalent of the Fourier shift theorem to derive a general one-dimensional integral transform for the application and removal of certain seismic data processing steps. This derivation comes from the observation that many seismic data processing steps can be viewed as nonstationary shifts themselves. The nonstationary frequency and time distortions inherent to many seismic data processes are predicted and quantified by this transform. Once the transform is developed, I demonstrate matrix-vector multiplication as a valuable tool for implementation. I use the normal moveout (NMO) correction and Stolt migration as examples. Displaying the integration kernel matrices yields insight to the mechanics of their respective transforms, and also reveals symmetries that can be exploited to improve computational efficiency. Matrix-vector multiplication is an intensely studied field in applied mathematics and computer science, so there are many algorithms available to further increase efficiency. Most of these algorithms offer a trade-off between accuracy and efficiency, and some even offer to quantify the error associated with their approximation. Unlike conventional processing algorithms that require interpolation, data processing steps performed by matrix vector multiplication are reversible within computational accuracy. I show that interpolation schemes are a frequency band-limited approximation to the transform method I develop. Just as the Fourier inversion theorem justifies the Fourier domain as a valid processing domain, the reversible data processing transform quantitatively justifies using processed data as if it is in a new domain.

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TEMPORAL AND SPATIAL SULFATE VARIABILITY IN GROUNDWATER AT A LIGNITE MINE, NORTHEAST TEXAS

Margaret Frances Cagle, M.S. Geo. Sci.

The University of Texas at Austin, 2007

 

Supervisor: John M. Sharp

Sulfate (SO 4 2- ) concentrations in the groundwater at the Luminant Monticello lignite mine, northeast Texas, vary with both time and space.  SO 4 2- is monitored closely because it is a product of chemical reactions that can lead to acid mine drainage. Although acid mine drainage is not a problem at Monticello, SO 4 2- concentrations in some areas are high and correspond to high total dissolved solids (TDS), low pH groundwater. At Monticello, chloride, total dissolved iron, and total dissolved manganese concentrations also are variable. To examine this variability, 46 monitoring wells are divided into those: 1) screened in rock underneath the lignite seam (underburden); 2) screened in the rock over the lignite seam (overburden); and 3) screened in the reclaimed spoil.  There is a wide range of SO 4 2- concentration across the mine with statistically significant differences between the SO 4 2- distributions for each well category.  Three hypotheses may explain the spatial SO 4 2- variability: (1) The heterogeneity of the mined material (2) Flushing of SO 4 2- from the reclaimed section into the overburden (3) Exposing iron sulfides to oxidizing conditions when the water table is dropped by mine dewatering operations.  Possible sources of SO 4 2- include the oxidation of pyrite and/or the dissolution of gypsum.

Temporal SO 4 2- variability is evident in the SO 4 2- time series for each well.  In the underburden, SO 4 2- seems to be approaching a steady state; however, some wells in the unmined overburden and reclaimed area have SO 4 2- trends that are increasing or are highly variable with time. Water table fluctuations or flushing caused by seasonal meteorological changes may control these trends.

Correlation analyses show that for most underburden, overburden, and reclaim wells, SO 4 2- does not correlate with pH, indicating that acidity does not accompany the incorporation of SO 4 2- and that SO 4 2- may be advected from another part of the mine. Analysis of water level and SO 4 2-  time series, as well as Cl - and SO 4 2- time series, show that advection from reclaimed areas cannot account for every high SO 4 2- value or increasing SO 4 2- concentration in the overburden and reclaim.   Groundwater in most overburden and reclaimed areas are at equilibrium with gypsum, indicating gypsum precipitation if SO 4 2- is flushed into the area and gypsum dissolution if SO 4 2- is flushed out.

Time series analyses shows some of the wells with increasing SO 4 2- concentration to be approaching equilibrium. Also, most SO 4 2- time series have a seasonal component. Flushing from the reclaimed areas is considered to be the dominant process controlling SO 4 2- variability in the overburden. A combination of flushing and aqueous geochemical processes related to heterogeneity controls the SO 4 2- concentration in the reclaimed land.

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DEVELOPMENT OF THE LOS CHIVOS PLATFORM, A PALEOCENE CARBONATE BUILDUP IN A SILICICLASTIC DOMINATED SALT BASIN, LA POPA BASIN, NORTHEAST MEXICO

Mathew Allan Campbell, MS Geo Sci

The University of Texas at Austin, 2003

Supervisor:William L. Fisher for R. K. Goldhammer (Deceased)

118 pages, 31 references, 4 plates

The stratigraphic development of carbonate platforms in the Gulf of Mexico region are subject to many controlling factors. While eustasy, regional subsidence, and sediment production are important elements, the effect of local syn-depositional tectonics, related to diapiric movement of mobile evaporite, is also locally vital. Uplift and subsidence caused by salt movement probably were critical factors in the development of the Los Chivos Lentil in the La Popa foreland basin of northeast Mexico.

The Los Chivos Lentil is a 16 sq. km isolated Paleocene carbonate platform that probably formed on a salt-supported anticline. Several other carbonate platforms in the basin formed on salt related topographic highs found within the Upper Mudstone Member (i.e.during maximum flooding conditions) of the Potrerillos Formation in the Difunta Group. The Difunta Group represents roughly 5,000 meters of Maastrichtian to Eocene fluvial-deltaic clastic sediment shed from an area west of the Sierra Madre Oriental. The low clastic influx at the time of deposition for the Upper Mudstone Member allowed for vertical migration of underlying, Jurassic-aged, evaporite. These evaporite diapirs provided the bathymetric relief necessary to initiate carbonate sedimentation.

The Los Chivos Lentil consists of two major carbonate outcrops, the Los Chivos mesa and the Chivos Ridge section. The Chivos Ridge outcrop represents in situ carbonate sedimentation consisting of isolated red algal and coral buildups found on the western margin of the outcrop. The section exposed on the Los Chivos mesa is approximately 80-100 meters thick and primarily consists of thin-bedded, mixed skeletal packstones and grainstones transported from the in situ buildup and deposited on the eastern limb of the Chivos Anticline. A well exposed face of the mesa reveals large, seismic scale, off-lapping clinoform geometries in the allodapic sediment beds. Because of its good preservation and exposure, this platform provides an excellent location to study how carbonate deposition is affected by active salt tectonics. Development of this, and other La Popa Basin buildups, closely resembles modern sedimentation found on salt highs in the southern Persian Gulf and the Gulf of Mexico. This outcrop can also be used as an analog for buildups found in the subsurface.

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Integrating Seismic Geomorphology into improved reservoir models of Shelf Margin Deltas, Corallita/Lantana Field, Trinidad

Terence Campbell, MS. GeoSci

The University of Texas at Austin , 2006

Supervisor : Lesli Wood

This project analyzes the reservoir architecture and compartmentalization of the as yet undeveloped Corallita and Lantana gas fields. Corallita-Lantana, discovered by Amoco Production Company in 1995, is an undeveloped dry gas discovery in the Greater Mahogany region offshore in the eastern shelf of the Columbus Basin , offshore S.E. Trinidad (Wood, 2004). It is currently estimated to contain 1.5 TCF of gas resource in Pleistocene age reservoirs.

Several factors complicate development of the Corallita-Lantana field, including fault seal, trap definition and reservoir compartmentalization. 1120 km 2 of 3D seismic combined with well log analysis have been used to explain the reservoir shape, size and distribution. Seismic coherency, amplitude analysis and spectral decomposition have been integrated to improve understanding of reservoir heterogeneity and compartmentalization, and spatial changes in reservoir petrophysics. Such knowledge will enable engineers to establish the best production design, and implement the most economical artificial drive mechanism for production.

I made statistically robust, geomophometric analysis of the reservoir by assigning binary codes to various facies and incorporating well log character using cumulate analysis software on interactive computer workstations. The reservoir of interest (TQ60) shows varying seismic facies architecture from shelf to slope. The seven seismic facies identified are conformable topset facies, interchannel facies, canyon facies (mass transport deposits), channel levee systems, ponded turbidities, conformable horizontal slope facies and faults which are identified on seismic attributes extractions. Assigning digitized codes to different facies is a fast and effective way to model a reservoir and compare different data sets.

The result of combining geomorphology from seismic attributes to reexamine the stratigraphic framework is a predictive tool that strengthens any model from sediment content, basin plays characterization, risking prospects and well placement models. Development of the field is now being planned and approximately 56% of the reserves are in the Pleistocene age TQ60 sand across both the Lantana and Corallita fault segments. Results from this study do not only apply to the development of the field, but explain how reservoir shape and distribution can be addressed in all shallow marine and fluvial-deltaic environments.

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STRUCTURAL AND PETROGRAPHIC ANALYSIS OF CAMBRIAN ROCKS AT BEAVERTAIL STATE PARK, NARRAGANSETT BASIN, RHODE ISLAND

Matthew J. Carter, M.S.

The University of Texas at Austin, 2008

Supervisor: Sharon Mosher

85 pages, 26 references, 3 glossy plates

Structural Mapping at 1:1000 scale of the Cambrian rocks within Beavertail State Park, Narragansett Basin, Rhode Island has revealed an early open to isoclinal fold generation (F1) and axial planar foliation (S1) followed by a later, more prominent, E-vergent, N-trending non-coaxial fold generation (F2) and associated foliation (S2). A third map-scale folding phase is inferred from the NNE-trending, broad warping of S2. Quartz veins are folded by and cross cut F2 folds. N-S to NE-SW extension resulted in 1-10 m scale boudins that deform S2. All of these structures are cross cut by NNE to ENE-striking faults and joints. Kinematic indicators show that the dominant motion on these faults was normal with minor sinistral and/or dextral motions. The Beaverhead Shear Zone that juxtaposes the Cambrian rocks with Pennsylvanian rocks of the Narragansett Basin deflects S2 in a dextral sense, consistent with recorded motion elsewhere. Kink bands associated with faulting trend NNE to ENE and display WNW to NNW side up.

Petrographic work reveals S1 is a penetrative foliation defined by alignment of white micas. S2 is a crenulation cleavage of S1 that is enhanced by pressure solution. S2 is the dominant foliation expressed in the field; however there are areas where S1 is locally better developed. Siderite and quartz nodules overgrow S1 and are wrapped by S2. Mica, quartz and iron carbonate pressure shadows on these nodules are parallel to S2.

Fabric development and orientation, style, and sequence of structures found in the lower greenschist Cambrian rocks within and up to 4 km north of Beavertail State Park, RI are dissimilar to those associated with the Taconic and Acadian events, but identical to Alleghanian structures in Pennsylvanian aged rocks of the Narragansett Basin. These similarities indicate that the Cambrian rocks have exclusively recorded the Pennsylvanian-Permian Alleghanian orogeny, and could not have been in place in North America during the Ordovician Taconic and Devonian Acadian orogenies. Timing constraints indicate the collision of the Avalon microcontinent occurred during the late Pennsylvanian, whereas progressive deformation of the Pennsylvanian rocks of the Narragansett Basin and the Cambrian rocks took place during the Permian.

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EVOLVING SUBGLACIAL WATER SYSTEMS IN EAST ANTARCTICA FROM AIRBORNE RADAR SOUNDING

Sasha Peter Carter, PhD

The University of Texas at Austin, 2008

Supervisor: Donald D. Blankenship

241 pages, 162 references, 16 tables

The cold, lightless, and high pressure aquatic environment at the base of the East Antarctic Ice Sheet is of interest to a wide range of disciplines. Stable subglacial lakes and their connecting channels remain perennially liquid three kilometers below some of the coldest places on Earth. The presence of subglacial water impacts flow of the overlying ice and provides clues to the geologic properties of the bedrock below, and may harbor unique life forms which have evolved out of contact with the atmosphere for millions of years. Periodic release of water from this system may impact ocean circulation at the margins of the ice sheet.

This research uses airborne radar sounding, with its unique ability to infer properties within and at the base of the ice sheet over large spatial scales, to locate and characterize this unique environment. Subglacial lakes, the primary storage mechanism for subglacial water, have been located and classified into four categories on the basis of the radar reflection properties from the sub-ice interface: Definite lakes are brighter than their surroundings by at least two decibels (relatively bright), and are both consistently reflective (specular) and have a reflection coefficient greater than –10 decibels (absolutely bright). Dim lakes are relatively bright and specular but not absolutely bright, possibly indicating non-steady dynamics in the overlying ice. Fuzzy lakes are both relatively and absolutely bright, but not specular, and may indicate saturated sediments or high frequency spatially heterogeneous distributions of sediment and liquid water (i.e. a braided steam). Indistinct lakes are absolutely bright and specular but no brighter than their surroundings. Lakes themselves and the different classes of lakes are not arranged randomly throughout Antarctica but are clustered around ice divides, ice stream onsets and prominent bedrock troughs, with each cluster demonstrating a different characteristic lake classification distribution.

In the bedrock trough of Adventure Subglacial Trench, analysis of satellite altimetry is combined with radar sounding data to calculate a mass budget and infer a flow mechanism for a two cubic kilometer discharge reported to have traveled between two lakes in the region from 1996 – 1998. The volume released from the source lake exceeded the volume received by the destination lakes by one and a tenth cubic kilometers, indicating that some water must have escaped downstream from the lowest destination lake over the course of the event. Release of water from the source lake preceded arrival of the water at the destination lakes, 260 kilometers away, by about three months. Water continued draining from the destination lakes for several years after surface subsidence at the source lake had ceased. By 2003, a total of one and a half cubic km or nearly 75% of the water released by the source lake had traveled downstream from the destination lakes.

Hydraulic modeling work indicates that the initial release of water from the source lake could have been accommodated by a self-enlarging semicircular channel. Subsequent evolution of the discharge and the three-month delay between release of water from the source lake and arrival of that water at the destination lakes indicates that a shallower and broader distributed water system is responsible for the transport of subglacial water in this region. Such a system would be more stable for the given ice-bedrock geometry and may explain the observations of intermittent flat bright bedrock reflections in radar data acquired upstream from the destination lake in 2000.

For the purpose of better understanding the long-term water budget of the Dome C region, an area upstream of Adventure Trench, eleven dated isochronal internal layers within the ice penetrating radar data were tracked. An age-depth relationship, derived from the European ice core through Dome C is used to calculate strain, estimate melt, model ice temperature, and determine absolute basal reflectivity for the entire region which covers over 28,000 square kilometers. The two largest subglacial lakes within the survey, Concordia and Vincennes, are both associated with enhanced basal melting on their upstream shores at rates locally greater than two millimeters per year. Widely distributed melt rates in the major topographic valleys upstream of these lakes are generally less than one millimeter per year throughout the region with slightly higher melts in the basin draining into Vincennes Subglacial Lake. Although published estimates for geothermal flux are capable of explaining the behavior of ice and water in most of the area, an additional source of basal heat is required to explain melt anomalies and subglacial lakes along the Concordia Ridge. Lake Concordia is expected to discharge water on a similar scale and duration as that observed in Adventure Trench, with a repeat cycle of a few hundred years.

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SEDIMENT VOLUME PARTITIONING, TOPSET PROCESSES AND CLINOFORM ARCHITECTURE –UNDERSTANDING THE ROLE OF SEDIMENT SUPPLY, SEA LEVEL AND DELTA TYPES IN SHELF MARGIN BUILDING AND DEEPWATER SAND BYPASS: THE LANCE-FOX HILLS-LEWIS SYSTEM IN S. WYOMING

Cristian Rene Carvajal, Ph.D.

The University of Texas at Austin, 2007

Supervisor: Ronald J. Steel

171 pages, 133 references, 3 tables

This research focuses on how sediment supply, sea level and delta processes control the partitioning of the sediment budget across and into the topset, slope and basin-floor compartments of deepwater basins. Addressing this problem provides significant insight to characterize source-to-sink systems, improve tectono-stratigraphic models and predict sand bypass to deepwater areas. The research was carried out in the Lance-Fox Hills-Lewis shelf margin formed during the Maastrichtian in the Washakie-Great Divide basin of southern Wyoming. I use a database with approximately 520 wells integrated with outcrops to develop a high resolution, dynamic stratigraphy approach for shelf-margin characterization.

The results emphasize the driving role of sediment supply in rapid shelf-margin building and deepwater sand emplacement. On the study margin, high sediment supply was able to outpace shelf accommodation even at times of relatively high and rising sea level. At these times, shelf margin clinoforms developed a more aggradational architecture with relatively thick and more marine influenced topsets formed in response to basin deepening due to rapid subsidence. The high supply and subsidence are interpreted to have resulted from crustal loading and significant erosion during prominent Laramide thrust-driven source uplift. The high supply caused the formation of highstand shelf-edge deltas with strong wave and river influences. These deltas resulted in extensive coastal sand belts at the shelf margin, and bypass of significant volumes of sand to deepwater areas. In contrast, during times of stable to very low rates of sea level rise, the basin developed more progradational clinoforms with more terrestrial and generally thinner topsets. More of the sediment was funneled to the basin floor and shelf-edge deltas were under strong river and tidal influence. Stable or even falling sea level resulted from decreased subsidence or slight basin uplift, interpreted to have resulted from decreasing uplift, tectonic quiescence or possibly slight tectonic rebound in the basin. The Lewis-Fox Hills margin is considered supply-dominated, a term to denote moderately deep shelf margins (< 1000 m) that prograde at high rates (several tens of km/my) and deliver sand to deepwater areas recurrently and in large volumes even at sea level highstand.

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SEQUENCE STRATIGRAPHY AND TECTONICS OF THE GUANTAO AND MINGHUAZHEN FORMATIONS, ZHAO DONG FIELD, BOHAI BAY, EASTERN CHINA

Hugo Alberto Castellanos, Ph.D

University of Texas at Austin, 2007

Supervisor: William L. Fisher

242 pages, 157 references, 5 tables

The Cenozoic tectonic evolution of the Bohai Basin in eastern China has been documented through the interpretation and integration of 8,000 km of offshore 2D seismic data, a 3D seismic volume, and 38 well logs that are tied to these reflection data. The Cenozoic stratigraphy of this basin records: 1) a late Paleocene-late Oligocene basin opening across a diffuse set of half-grabens; the widespread distribution of rifts in the Bohai Basin and adjacent areas supports a regional extension possibly related to a previously proposed rollback of the subducted Pacific plate beneath the Asian continent; 2) a late Oligocene uplift and regional erosional event marking the end of major rifting; 3) early Miocene widespread thermal subsidence manifested by a large, relatively unfaulted sag basin; and 4) middle Miocene to recent strike-slip faulting; the regional- scale "lazy-Z" map pattern of the Bohai Basin depocenter indicates the importance of right-stepping pull-apart control on the younger sag section. Initiation of strike-slip deformation in the basin is attributed to a change in the direction of the convergence vector from WNW-ESE to E-W between the Eurasian plate and the subducting Pacific plate during early to late Miocene time.

The Miocene Guantao and Pliocene Minghuazhen Formations in Zhao Dong field, western Bohai Bay, represent a 1.7-km-thick fully continental succession deposited in a large sag basin formed during the post-rift, early Miocene and younger thermal subsidence stage of the Bohai Basin. Correlation of 38 closely spaced wells and mapping of 2D and 3D seismic data in the 280 km2 Zhao Dong oil field allowed correlation and chronostratigraphic subdivision of these fluvial deposits into ten fieldwide and correlatable accommodation/supply cycles.

Seismic mapping, well-log correlations and total sand thickness maps estimated from impedance volumes revealed two styles of sand distribution in Zhao Dong field: channel-fill facies in the Minghuazhen Formation are intermittently and locally deposited within a background matrix of high-impedance floodplain facies. Channel-fill facies in the Guantao Formation are highly amalgamated and form areally extensive fluvial sandstone bodies that extend several hundred meters along dip and strike directions.

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STRUCTURAL ANALYSIS OF CENOZOIC FAULT SYSTEMS USING 3D SEISMIC DATA IN THE SOUTHERN MARACAIBO BASIN, VENEZUELA

Maria Veronica Castillo, PhD

The University of Texas at Austin, 2001

Supervisor: William L. Fisher

The Icotea and VLE 1 faults are two of the major faults in the Maracaibo Basin, Venezuela, and are known from seismic and well data to have been most active during Paleogene time. Both faults have linear traces over distances up to 100 km, are deeply buried under largely unfaulted Neogene sedimentary rocks, and are associated with localized continental growth strata of Paleogene age along their traces. The origin and displacement history of both faults has remained controversial partly because of along-strike complexities in fault structure, use of highly exaggerated 2D seismic lines, and the lack of synoptic views of both fault systems. Previous interpretations range from east dipping basement-involved thrust faults to sub-vertical left-lateral strike-slip faults controlling pull-apart basins. I use regional 2D seismic data crossing both faults, and 3D seismic data covering a 1600 km 2 area of the southern Maracaibo Basin to describe structures along the traces of both faults and fault termination structures at their southern ends. These seismic reflection data show that both faults are inverted normal faults that first formed during the late Jurassic-early Cretaceous. The abrupt termination of both faults in the southern part of the basin probably corresponds to the southern ends of two parallel rift structures. This study also uses 3D seismic reflection data to describe a karst horizon in the Aptian-Albian carbonate rocks that may have formed during a worldwide eustatic drop in Albian sea level that also produced the well-known mid-Cretaceous unconformity recognized in the Gulf of Mexico, France, and Middle East. The karst interpretation may allow a better understanding of reservoir characteristics at this level in the carbonate platform, which are generally attributed to fracturing rather than subaerial weathering. The presence of a regionally extensive karst surface at depth beneath other basins along the northern margin of South America may prove to be a useful oil exploration play concept.

1 VLE fault: named by the Petróleos de Venezuela filial MARAVEN S.A., to describe a NS striking fault in Block V located in the central area of the Lake Maracaibo.

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THREE-DIMENSIONAL STRATAL DEVELOPMENT OF A CARBONATE-SILICICLASTIC SEDIMENTARY REGIME, NORTHERN CARNARVON BASIN, NORTHWEST AUSTRALIA

Donna Louise Cathro, Ph.D.

The University of Texas at Austin, 2002

Supervisors: William L. Fisher and James A. Austin, Jr.

Detailed stratigraphic interpretation of continental margin clinoforms is a necessary first step in understanding the link between this complex stratal architecture and large-scale processes resulting in progradation. Maps derived from a 3D seismic volume (40-55 Hz) nested within a regional 2D multichannel seismic grid (25-35 Hz), and tied to nine hydrocarbon exploration wells, show the detailed morphological evolution of five prograding clinoformal sequences in the Northern Carnarvon Basin (NCB), northwest Australia.

Depocenters concentrated along northeast-southwest oriented, linear clinoform fronts are governed by latitudinal variations in sediment productivity. Fronts change from smooth to highly dissected, with intense gullying apparent after the mid Miocene optimum. Bottomsets remain relatively sediment-starved without the development of aprons on the lower slope and basin. Small-scale variability suggests heterogeneous sediment dispersal through these slope conduits. Along-strike sediment transport superimposed on northwest-oriented progradation changes from south-directed in the late Oligocene to north-directed in the late mid-Miocene suggesting a reorganization of circulation in the southeastern Indian Ocean.

Prominent seismic discontinuity surfaces represent intervals of shallow paleo-water depth and flooding of the shelf. Exposure surfaces are subordinate. Rather than build to sea-level, progradation occurs with shelf paleo-water depths of 20-200 m. Therefore, onlap onto the clinoform front is not coastal and the sensitivity of the clinoforms to sea-level changes is muted. However, in the mid-Miocene, partial exposure of the shelf and development of karst topography indicate paleo-water depth falls of 60-180 m across two sub-sequence boundaries.

The sequence stratigraphic framework is combined with a two-dimensional, forward kinematic and flexural model for deformation of the lithosphere to determine the distribution, magnitude and history of Cretaceous-Tertiary compression-induced inversion across the Dampier Sub-basin in the NCB. Inversion simultaneously creates and destroys accommodation space at different wavelengths superimposed on long wavelength subsidence and eustatic variations that impact the entire margin. Inversion anticlines focused along earlier rift fault systems are small, temporally and spatially variable relative to the total accommodation space created in the sub-basins during rifting and thermal subsidence. Santonian inversion represents ~4 km shortening, whereas the four modeled events in the Miocene each represent ~200-400 m of shortening across the modeled section.

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TIME-LAPSE (4-D), VP/VS INTERPRETATION OF RESERVOIR DEPLETION IN TEAL SOUTH FIELD, GULF OF MEXICO

Fernando Antonio Cerda, M. S. Geo Sci.

The University of Texas at Austin, 2001

Supervisor: William L. Fisher

Multicomponent seismic data over the producing reservoirs in Teal South field, located 160 miles southwest of New Orleans, were analyzed to detect changes and describe reservoir changes over time. The primary seismic objectives of the analysis were to monitor: hydrocarbon movement; distinguish sand fill from shale within the 4500 ft sand using the ratio of seismic wave velocities (Vp/Vs); map actual reservoir boundaries; and compare Vp/Vs ratios from different time-lapse observations. Conventional P-wave seismic velocity is not a good lithologic indicator because of the overlap in P-wave velocities ranges for various rock types. The additional information provided by the converted-wave data reduces the ambiguity in lithological and hydrocarbon interpretation.
In July 1997, an Ocean Bottom Cable (OBC) survey was performed at Teal South using a sparse, fixed-position receiver grid (Phase I). In order to achieve adequate fold, a dense grid of shots was acquired over an area extending 1000 m in all directions around the areal receiver grid. The dense source grid covered an area of about 9 km2. The receiver spread was stationary for the entire source grid. In April 1999 (Phase II), a repeat survey was recorded for time-lapse comparison to the base survey.
After processing, the data quality observed in the prestack and migrated data was good, although significant migration artifacts were visible at the edges of the survey, especially on the mode converted-wave data. An acquisition footprint effect was also observed shallow in the section, related to the sparse receiver spacing and possibly affected by the shooting direction.

The interpretation of the P-wave data focused on identifying high reflection contrast (4500 ft sand), and analyzing reflection amplitude differences related to fluid properties of the reservoir between initial and repeat surveys. This latest aspect reveals characteristics of the dynamic response of the bulk rock/fluid properties to the changing fluid conditions. The high production rate in the reservoir resulted in the expansion of the gas cap, due to gas exsolving from the oil. As a result, a pressure loss may have prevented production of a significant amount of remaining oil.

Interpretation of the mode-converted (P-SV) wave volume was guided by the interpretation of the P-wave volume and proceeded by picking and mapping a number of reflection events in both the orthogonal-component volumes (components C1 and C2) for phases I and II, respectively. The strongest and most continuous reflections were visually correlated from the P-wave data set to the mode-converted wave data set to reduce ambiguity of misinterpreting weaker or minor events. Experiments with different horizons were done to calculate the Vp/Vs ratio. Large intervals between horizons were avoided so that the measurements were not influenced by properties outside the interval of interest.

The interpretation of the velocity ratio Vp/Vs for phase I, shows lower values of Vp/Vs that define the shape of the reservoirs and show a separation between different producing reservoirs in Teal South. In phase II (21 months later), it is possible to observe a expansion of low values of Vp/Vs all around neighboring sands (Sand A). This spatial expansion of low Vp/Vs ratio coincides with the gas cap expansion observed in the P-wave volume in phase II. In general, correlation of P-wave and S-waves was complicated by the lack of a multicomponent Vertical Seismic Profile (VSP) and well log information that can define which P-wave reflections coincide with selected S-wave reflections.

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DISSOLVED NOBLE GASES IN GROUNDWATER

Bradley Donald Cey, Ph.D

The University of Texas at Austin, 2008

Supervisor: Bridget R. Scanlon

179 pages, 114 references, 9 tables

Atmospheric noble gases (He, Ne, Ar, Kr, and Xe) dissolved in groundwater are a valuable tool in hydrology. Numerous studies have relied on groundwater recharge temperatures calculated from dissolved noble gas data (noble gas temperatures, NGT) to infer paleoclimate conditions. This research investigated gas dissolution during groundwater recharge and critically examined the use of dissolved noble gas data in groundwater research. A detailed investigation of an agriculturally impacted shallow aquifer allowed comparison of measured water table temperatures (WTT) with calculated NGT. Results suggest that NGT calculated from widely used noble gas interpretive models do reflect measured WTT, supporting the use of dissolved noble gases to deduce recharge temperatures. Samples having dissolved gas concentrations below the equilibrium concentration with respect to atmospheric pressure were attributed to denitrification induced gas stripping in the saturated zone. Modeling indicated that minor degassing (<10% Δ Ne) may cause underestimation of groundwater recharge temperature by up to 2 °C. In another study a large dissolved noble gas data set (905 samples) from California was analyzed. Noble gas modeling using the same interpretive models indicates that multiple models may fit measured data within measurement uncertainty, suggesting that goodness-of-fit is not a robust indicator of model appropriateness. A unique aspect of this study was the high Ne and excess air concentrations associated with surficial artificial recharge facilities. A final study examined whether climatic/hydrologic changes occurring over glacial-interglacial time periods could impact the accuracy of NGT used in paleoclimate studies. Numerical modeling experiments estimated WTT sensitivity to changes in: 1) precipitation amount, 2) water table depth, and 3) air temperature. Precipitation and water table depth had a minor impact on WTT (~0.2 °C). In contrast, the impact of air temperature changes on WTT was more pronounced. Results suggest that air temperatures inferred from NGT data may underestimate actual air temperature change since the last glacial maximum by ~1 °C at sites having seasonal snowcover. These results suggest despite uncertainty in the exact physical processes controlling gas dissolution during groundwater recharge, NGT do reflect WTT. However, inferring paleo-air temperatures from NGT are subject to error, especially locations with seasonal snowcover.

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EVOLUTION OF THE TOBAGO FOREARC BASIN: IMPLICATIONS FOR SEDIMENTATION AND HYDROCARBON PRODUCTIVITY

Nysha Alana Niela Chaderton, M.S.

The University of Texas at Austin, 2005

Supervisor: Lesli Wood

The relationship of the Lesser Antilles Island Arc, the Tobago Forearc Basin and the Barbados Accretionary Prism shows classic convergent margin/subduction zone geometry. The island of Barbados is the only emergent part of the accretionary prism, with 80% of the land area being covered by Pleistocene limestone which has been eroded in the NE to expose the older rocks of the accretionary prism. A 450 km 2 2D seismic data volume allows for the extension of these stratigraphic units offshore and allows for the definition of a structural framework for the region. The relationship between the unit identified onshore as the Early Eocene to Middle Miocene Oceanic Formation and the basal unit, the intensively folded and faulted Eocene Scotland Formation, has long been cause for debate. It has been previously proposed that the Oceanic Formation, which consists of pelagic clays with some ash beds, is allocthonous and has been thrusted into its present position, overlying the accreted sediments of the Scotland Formation. However the seismic data shows no evidence of the nappes which are the basis for this theory. The opposing theory is that the Oceanic Formation is related to the 12 km of sediment which fills the Tobago Forearc Basin and has been deposited in situ. This is supported by the relationships between the seismic facies which shows the onlap of the Oceanic Formation onto the older accreted sediments.

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THE RELATIONSHIP OF MAMMALIAN MORPHOMETRIC DIVERSITY TO ENVIRONMENTAL VARIATIONS AND ITS USE IN PALEOCLIMATIC RECONSTRUCTIONS

John Lee Chaille, PhD

The University of Texas at Austin, 2001

Supervisors: Ernest L. Lundelius, Jr. and Timothy B. Rowe

The morphometric variation in the skulls of six species of mammals from North America (Canis lupus, Castor canadensis, Lynx rufus, Mephitis mephitis, Odocoileus virginianus, Procyon lotor) with broad geographic ranges is statistically analyzed. The morphometric characters are used along with climatic temperature and rainfall variables to determine the degree of relationship between these two sets of variables. The number of morphometric variables varies from twelve to seventeen different measurements, depending on the species; whereas the climatic data set consists of four temperature-related and four rainfall-related variables. The morphometric variables for all of the species, except one, have a higher percentage of significant correlations with the temperature-related variables than with those for rainfall. The exception, Procyon lotor, has a slightly higher percentage of rainfall related correlations that are significant. The t test, Hotelling T2 test, and discriminant analysis indicate varying degrees of sexual dimorphism in the morphometric characters, from relatively weak in Castor canadensis to very strong in Canis lupus and Odocoileus virginianus. This prompts the analyses of the male and female specimens both separately and together in many of the statistical tests. The robustness of making climatic variable predictions using multiple regression varies between the species. Mephitis mephitis and Odocoileus virginianus have the best overall prediction results, although each species has some accurate along with some not-so-accurate prediction results. A higher percentage of accurate predictions occurs in the analyses related to temperature. The understanding of the relationship of morphometric variation in the skulls of Recent widespread mammalian species, and the relationship of that variation to the climatic variation over the species ranges can be useful in paleoclimatic reconstructions.

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AN INTEGRATED GEOLOGIC MODEL OF VALHALL OIL FIELD FOR NUMERICAL SIMULATION OF FLUID FLOW AND SEISMIC RESPONSE

Samarjit Chakraborty, MS

The University of Texas at Austin, 2007

Supervisor: Dr. Robert Ferguson

Time-lapse seismic monitoring promises to be a valuable tool for reservoir engineering as it provides dynamic data over the entire ?eld rather than the spatially limited production data. In this thesis, I develop a link between computerized reservoir simulation, rock physics, and seismic analysis. I present an example study of time-lapse seismic e ? ects in a sequence of reservoir simulation, rock physics, and seismic forward modeling. The thesis includes a case-study of the Valhall ?eld which I propose be used for an integrated geologic model for ?uid ?ow and seismic simulation.

I combine ?uid ?ow simulation studies with a parallel ?ow simulation code IPARS to obtain computed pore pressure and oil saturation at di ? erent spatial location as a function of time. The reservoir model for ?uid ?ow simulation input is linear and isotropic. The reservoir model has an injection well below the oil-water contact and a producer well at a shallower level. The variations of pore pressure due to injection and production cause 3-D multi-phase ?uid ?ow in the reservoir with time.

I develop a rock physics mapping code to estimate the P-wave and S-wave seismic velocities and densities for seismic forward modeling from pore pressure and water and oil saturation obtained by ?uid ?ow simulation. The rock physics code uses Gassmann's relations for ?uid substitution to compute the seismic re?ection parameters.

Migrated depth sections show brightening of amplitude values near the producer well as a function of time. Re?ections from the production zone appear stronger indicating high oil saturation values with increasing production.

I develop a case-study of the Valhall Field to make an integrated geologic model for ?uid ?ow and seismic simulation. Based on an initial description of reservoir geology, I combine rock-physics measurements, ?uid properties, geomechanics, seismic, well, and checkshot data, to build an integrated model for simulations of subsurface ?uid-?ow and surface seismic data.

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STRUCTURAL GEOLOGY OF THE PACHECO PASS AREA, DIABLO RANGE, CALIFORNIA: EXHUMATION OF A COHERENT BLUESCHIST TERRANE IN THE FRANCISCAN SUBDUCTION COMPLEX

Kirk Chatawanich, M.S. Geo. Sci.

The University of Texas at Austin, 2001

Supervisor: Mark Cloos

The world's largest terrane of coherently bedded blueschist-facies metamorphic rocks containing jadeitic pyroxene plus quartz is exposed in the Franciscan Complex core of the Diablo Range of Central California. Petrologic studies by W .G. Ernst and others have shown that peak metamorphic temperatures were in the range 150-250ºC and pressures were 7-8 kbar. Plate convergence explains how these sediments were subducted to depths of 25-30 km, but the exhumation of these rocks and juxtaposition against upturned strata of the Great Valley Group is problematical.

In the Diablo Range, Franciscan rocks deposited during the Late Jurassic Cretaceous are found in contact with Great Valley Group sedimentary rocks of roughly the same age across the high-angle Ortigalita Fault. North of San Francisco, the Great Valley strata are separated from the Franciscan by the sheared ultramafic and mafic igneous rocks of the Jurassic Coast Range Ophiolite. Isotopic age data indicate peak temperatures were attained around 100 Ma, and fission track thermochronology indicates a major period of cooling occurred at 100-70 Ma. Franciscan detritis began to appear in the geologic record in the Eocene at about 50 Ma. Volcanic rocks dated it 9-11 Ma are deposited on Franciscan rocks in the Diablo Range, indicating uplift and exhumation to surface levels had occurred by that time.

Near Pacheco Pass, California, Franciscan strata are exposed along a 4 km transect cut by California Highway 152 and a 3.1 km transect cut by the old road through the pass. Structural analysis along 4.3 km of total roadcut exposures was performed in order to determine average orientations of structures along the traverse. The Franciscan strata consist mainly of interlayered greywacke and shale with subsidiary beds of chert and rare conglomerate lenses. Paleotop indicators were found at only nine localities, and all but one indicate the nearby section is upright. In many roadcuts, individual beds can be traced for tens of meters. There is no evidence of a greenschist facies overprint, and the presence of aragonite veins indicates that exhumation to depths less than 10 km occurred under cool, syn-subduction geothermal conditions.

Franciscan strata exposed along the transacts contain numerous angular folds and quartz veins. Planar faults with thin cataclastic zones are common. The attitudes of 1280 bedding surfaces, 2297 metamorphic foliations, 1073 fold hinge lines, 4036 veins, and 109 faults were measured along the roadcuts. Metamorphic foliations are bedding-parallel and folded. Upright chevron folds with moderately to steeply dipping limbs are common in the central part of the field area along Highway 152 and near the Ortigalita Fault. Some veins are bedding/foliation parallel, but most are perpendicular to foliations and indicate NE-SW extension direction, roughly perpendicular to the Ortigalita Fault. Most fold axes have an average NE-SW trend. The bedding-parallel cleavage indicates bedding-perpendicular shortening, whereas many veins and normal faults indicate roughly NE-SW extension.

The structural geology of the jadeitic rocks near Pacheco Pass can be explained with a history in which strata deposited on the Farallon plate during the Mesozoic were subducted to depths of 20-30 km. Stratal coherency at the scale of tens of meters was largely maintained during subduction, deep accretion by underplating, uplift and exhumation. The folding of bedding-parallel cleavage, most veining, and faulting post-date peak temperatures. The metamorphic foliation., veins, normal faults, and folds are most simply explained as forming during a near-vertical syn-subduction exhumation driven by deeper-seated underplating. Over tens of m.y., this process drove deeply accreted sediments through the crystalline base of the overriding North American plate to form the Diablo Range anticlinorium in the forearc basin setting.

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SEISMICITY AND TECTONICS OF THE ARC SEGMENTATION IN THE SOLOMON ISLAND ARC, SW PACIFIC OCEAN AND THEIR RELATION TO SUBDUCTING BATHYMETRIC FEATURES

Ming-Chu Chen, M.S.Geo.Sci.

The University of Texas at Austin , 2007

Co-Supervisors: Cliff Frohlich and Fred W. Taylor

For the Solomon Island arc we evaluate arc segmentation as defined by seismological and geological evidence. Seismological evidence that defines arc segment boundaries includes seismicity patterns, aftershock areas for large earthquakes, focal mechanisms, and variations in seismic moment release; the geologic evidence is mostly information about Holocene vertical movements, drowned coastlines and especially uplifted coral reef terraces, sometimes augmented by dated coral samples. We identify three major tectonic regimes or supersegments that correspond respectively to the areas surrounding Bougainville, New Georgia, and Guadalcanal-San Cristobal Islands . We speculate that subduction of the young Woodlark spreading center is what distinguishes the central New Georgia supersegment from the two neighboring supersegments. The New Georgia supersegment has relatively higher uplift rates, smaller arc segments, and more small islands; prior to the 1 April 2007 M B w B 8.1 earthquake it had generally lower rates of seismic activity than the neighboring supersegments. Altogether we identify twenty two segment boundaries, including eleven major segment boundaries, four minor boundaries, and seven possible boundaries in the Solomon Islands . Generally the mean along-arc lateral extent of Solomons arc segments are smaller than segments reported in other island arcs; this may be real but it may occur simply because the high seismicity rates and coral-friendly tropical environment provide an unusually favorable situation for observing variations in vertical tectonic activity and thus segment boundaries.

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MICROFACIES AND DEPOSITIONAL ENVIRONMENTS OF SELECTED PENNSYLVANIAN CALCAREOUS ALGAL DEPOSITS FROM SOUTHERN U.S.A., AND APPLICATION OF INFORMATION TECHNOLOGY FOR SEDIMENTARY PETROLOGY TEACHING AND RESEARCH

Suk-Joo Stephen Choh, Ph.D.

The University of Texas at Austin, 2004

Supervisor: William L. Fisher

168 pages, 209 references

Pennsylvanian calcareous algal bioherms dominated by Donezella, Beresellid, and Cuneiphycus could potentially form prolific hydrocarbon reservoirs. Understanding the biological makeup and depositional settings of these carbonate buildups is imperative. To provide an understanding of the geological and biological processes controlling the formation of these buildups, three localities in the southern United States were studied by integrating field sampling, microfacies analysis, and microstratigraphic analysis.

A Lower Pennsylvanian Donezella- and siliceous sponge-dominated carbonate buildup from the Wapanucka Formation, Oklahoma is composed of irregular pockets of boundstone dominated by Donezella, worm tubes, microbial peloids and micrite, siliceous sponge spicule, and peloidal wackestone with other bioclasts. The most significant finding of this study is the recognition of delicate a Donezella framework or colony of thalli enclosing and forming constructional pores.

Upper Pennsylvanian Beresellid algal colonies from the Holder Formation, New Mexico, are the product of an in situ growth fabric and constituents of Beresellid algal colonies. The Beresellid boundstone fabric was created by bundles of tangled algal thalli growing at an angle or parallel with the bedding surface, in association with phylloid algae, foraminifera, Tubiphytes, and rare brachiopods and crinoid fragments.

The Lower Pennsylvanian Cuneiphycus-dominated buildups from the Marble Falls Formation, Texas are composed of irregular pockets of boundstone dominated by Cuneiphycus, Donezella boundstone, and peloidal wackestone with other bioclasts. The first account of the red alga Cuneiphycus building a delicate framework of thalli and building a small-scale framework is documented.

In order to effectively handle large numbers of digital images of thin sections used in this study, a new method for creating and authoring virtual carbonate thin sections in PDF format was devised that it is a highly flexible, and platform independent image digitization and content creation method. The significance of this approach is that an image of the thin section is preserved/created and as well as preserves a variety of valuable information about a specimen that can be directly linked to the image of the specimen itself.

Another method of building a digital petrography image archive was devised to supplement the labor-intensive nature of teaching optical petrography. The architecture, process, and lessons learned from developing an interactive multimedia CD-ROM tutorial in sandstone petrology for undergraduates is documented. This approach provides possible models for similar development in other fields of petrography or in any other field that utilizes large quantities of visual material, such as seismic or remote-sensing image interpretation.

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SILICATE SURFACE CHEMISTRY AND DISSOLUTION KINETICS IN DILUTE AQUEOUS SYSTEMS

Wan-Joo Choi, Ph.D.

The University of Texas at Austin, 2004

Supervisor: Philip C. Bennett

268 pages, 116 references

Organic acids from the biosphere are important reactants in a number of weathering environments. Organic acids accelerate silicate dissolution, increase silicate solubility, mobilize aluminum and silica, and alter the equilibrium between the solution and precipitated secondary phases. The chemical dynamics of the weathering environment was examined by investigating the interaction between mineral surfaces and organic/inorganic electrolyte solutions. Organic acids, analogs of microbially generated siderophores, were examined for their effects on aluminosilicate dissolution kinetics at multiple temperatures in various electrolyte solutions.

Mineral surface titrations were performed for six mineral samples: quartz, gibbsite, feldspars, microcline, andalusite, and kyanite. Mineral powder/distilled water mixture samples were titrated by 0.1 N HCl in the basic pH region, and by 0.1 N NaOH in the acidic pH region. UV-difference spectroscopic analysis was performed on dissolved silica-organic acid mixtures to characterize solution complexes. Mineral dissolution experiments were performed using temperature controlled, continuous-flow mixed reactors. For inorganic dissolution experiment, the solution ionic strength was controlled using LiCl while solution pH was adjusted using either dilute HCl or LiOH solutions. Reagent grade citric acid, tropolone, and 3,4-dihydroxybenzoic acid were used for organic ligand dissolution experiments. A constant flow rate was maintained by using a peristaltic proportioning pump. The mineral surface titration results revealed important surface properties that can be critical to interpreting dissolution kinetics in natural environments. One of the most important results would be that the amount of active surface sites can vary in different solution pH conditions which have been normally assumed to be fixed numbers based on surface area measurements. The UV-difference spectroscopy result shows that some siderophores form stable solution complexes with silica as well as Al and Fe. The results imply that dissolution of aluminosilicate minerals can be significantly enhanced in natural environments by bacterial siderophores, as suggested by previous researchers.

Dissolution results in inorganic electrolyte solutions showed that the net effect of solution ionic strength on the aluminosilicate dissolution reactions is a decrease in the overall dissolution rates, opposite to the effect of ionic strength on quartz dissolution. When the solution ionic species interact with feldspar surfaces, the mechanism of lowering the dissolution rates may be by inhibiting the ion exchange reaction. However, when the solution ionic species do not interact with the silicate surfaces or no ion-exchangeable species are available on the mineral surface, the mechanism of lowering the dissolution rate may be attributed to the effect of activity changes in the neutral species in the solution.

Microcline dissolution increased in organic ligand solutions relative to inorganic electrolyte solutions while andalusite and kyanite dissolution rates decreased in organic ligand solutions. The increased dissolution rate of microcline suggests that feldspar dissolution may be a S N2 mechanism. The decreased or unaffected dissolution rates from kyanite and andalusite suggest that the mechanism for these minerals may be a S N1 mechanism. The effect of organic ligands on dissolution rate was greater in pH 5 solutions than in pH 3. This result suggests that the dominant reaction mechanism in the pH 3 region is proton-promoted, while it is ligand-promoted in the pH 5 region.

Lower activation energies in organic ligand solutions suggest that: (1) the metal-organic complex is more stable at lower temperatures; or (2) the dominant reaction mechanism at a high temperature region may be proton-promoted and is ligand-promoted at a lower temperature region.

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CHARACTERIZATION OF BLUE GEM TOPAZ: A COMPARATIVE ANALYSIS OF TEXAS AND BRAZILIAN TOPAZ

Ana Collins, B.S.

The University of Texas at Austin, 2008

Supervisor: Mark Helper

The physical, optical and chemical characteristics of gem-quality Texas blue and colorless topaz were investigated with the goal of establishing sound criteria for differentiating Texas topaz from gem topaz from other pegmatite localities. Although higher prices are often associated with gem-quality Texas blue topaz, there is presently no qualitative or quantitative basis for this price difference. In addition, there is no way to independently verify a source of origin. It was determined that there are chemical and physical differences among gem topaz from the different localities, but these differences are not unique to each sample suite. The heterogeneity observed within the Texas and Brazilian samples themselves thus complicated the effort to find distinctive characteristics between the topaz from these two localities. Ultraviolet through infrared absorption spectra, X-ray diffraction-derived unit cell parameters, cathodoluminescence characteristics, and major- and trace-element concentrations were applied to arrive at a suite of identifying characteristics. Trace-element concentrations were expected to be the most important discriminator. Although trace-element concentrations are typically characteristic of the pegmatitic origins of the samples, no significant variation between sample suites was observed. Differences within and between sample suites likely represent differences in depth of emplacement, the amount of water present during crystallization, and/or trace-element concentrations within the pegmatitic melt.

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DEPOSITIONAL AND STRUCTURAL EVOLUTION OF THE MIDDLE MIOCENE DEPOSITIONAL EPISODE, EAST-CENTRAL GULF OF MEXICO

Ricardo Ignacio Combellas Bigott, Ph.D.

The University of Texas at Austin, 2003

Supervisor: William E. Galloway

291 pages, 137 references, 38 plates

Two widespread, transgressive deposits associated with the faunal top Amphistegina B (15.5 Ma) and Textularia W (12.1 Ma) define the Middle Miocene depositional episode. An extensive stratigraphic correlation framework established in this study allowed tracing of the middle Miocene sediment dispersal system from the shelf through the slope to the basin floor in the complex paleogeography of the east-central Gulf of Mexico. The Middle Miocene depositional episode is recorded in four genetic cycles (~1 to 2 Ma), bounded by regional maximum flooding surfaces in the shelf and shelf margin setting, and three equivalent seismic sequences punctuated by condensed sections in the slope and basin floor.

Two principal, long-lived extrabasinal fluvial/delta axes, the ancestral Mississippi and the Tennessee systems, provided the bulk of sediments that infilled the middle Miocene depocenters. Salt-related structural provinces controlled the configuration of the depocenters. Structural linked systems, dominated by gravity spreading, and a minibasin province, driven by differential subsidence, were established during the Middle Miocene depositional episode. Sediment supply coupled with wave energy flux, high-frequency sea-level changes, and salt tectonism determined the time and space distribution of progradation, aggradation, and retrogradation of system tracts.

Middle Miocene shelf margins have prograded 20 to 40 miles from the relict lower Miocene shelf margin. Two depositional systems tracts characterize the constructional shelf margin: (1) a mixed-load fluvial-dominated platform delta/ shelf-margin delta/delta-fed apron systems tract; and (2) a strandplain/shelf/muddy slope systems tract. However, the constructional, offlapping shelf margin systems were locally punctuated by a large-scale phase of retreat and erosion, named the Harang collapse system, in which a large volume of sediments bypassed the shelf margin to be deposited on the slope and basin floor. The Harang collapse system is a type of large-scale slope failure produced by massive salt-withdrawal, retreat of major delta systems, and high-frequency sea-level fluctuations.

A large volume of sediment bypassed the confined minibasin province and the unconfined Florida slope at the flank of active deltaic depocenters, forming the long-lived MCAVLU submarine fan system (named for its location beneath the Mississippi Canyon, Atwater Valley, and Lund continental shelf (OCS areas) in the linked, primary minibasin corridor of the lower slope and basin floor. The MCAVLU submarine fan system evolved from a structurally-controlled, elongate sand-rich to mixed sand/mud fan to a large radial, mixed sand/mud fan. Significant untapped middle Miocene hydrocarbon resources remain in the confined channel fills and lobes of the Harang collapse system and sand-rich ponded facies assemblages of the MCAVLU submarine fan system.

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MODAL ANALYSIS OF SAND FROM THE NANKAI ACCRETIONARY PRISM

Emily Comer, B.S.

The University of Texas at Austin, 2008

During the Cenozoic, complex plate interactions between the Philippine, Eurasian, and Pacific plates produced the Nankai Accretionary Prism off the southwest coast of Japan. As the Philippine plate subducts beneath the Eurasian plate, sediment from the volcanically active Izu collision zone northeast of the Nankai Trough travels down the trench and accretes tectonically into the prism. More quartz-rich forearc sediment from the Kii peninsula is also sedimented upon this prism by transportation down numerous submarine canyons.

Though the prism is deformed by numerous thrust faults, provenance identification is possible as documented in previous studies by Marsaglia (1992) and Fergusson (2005). In this study, 35 unconsolidated Cenozoic sand samples were thin-sectioned, point-counted, and analyzed. These samples were obtained in four sites (C0004, C0008, C0006, and C0007) by the Chikyu drilling vessel during NanTroSEIZE Expedition 316. QFL averages for Pleistocene samples is as follows; C0006 Q23F34L38; C0007 Q25F29L44; C0008 Q22F32L43; C0004 Q15F33L37. Only five Pliocene samples were collected in this study and all are more lithic-rich having an average composition of Q20F27L53. All 35 samples are classified as lithic arkoses or feldspathic litharenites within the Folk classification (Folk, 1982). QmKP and LmLvLs ternary diagrams show that plagioclase strongly dominates the feldspar assemblage and that volcanic and sedimentary lithics dominate over metamorphic lithics. Grain size between the four sites ranges from 3.75Ø (lower very fine) to .75Ø (lower coarse) with the mean being 2.75Ø (lower fine). Ternary plots dividing samples into 3 categories, 0.5-<2Ø, 2-<3Ø, and 3-4Ø show trends of increasing feldspar, quartz, sedimentary lithics abundance as grain size decreases.

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SPATIAL DELINEATION, FLUID-LITHOLOGY CHARACTERIZATION, AND PETROPHYSICAL MODELING OF DEEPWATER GULF OF MEXICO RESERVOIRS THROUGH JOINT AVA DETERMINISTIC AND STOCHASTIC INVERSION OF 3D PARTIALLY-STACKED SEISMIC AMPLITUDE DATA AND WELL LOGS

Arturo Javier Contreras, Ph.D.

The University of Texas at Austin , 2006

Supervisor: William L. Fisher & Carlos Torres-Verdin

This dissertation describes a novel Amplitude-versus-Angle (AVA) inversion methodology to quantitatively integrate pre-stack seismic data, well logs, geologic data, and geostatistical information. Deterministic and stochastic inversion algorithms are used to characterize flow units of deepwater reservoirs located in the central Gulf of Mexico. A detailed fluid/lithology sensitivity analysis was conducted to assess the nature of AVA effects in the study area. Standard AVA analysis indicates that the shale/sand interface represented by the top of the hydrocarbon-bearing turbidite deposits generate typical Class III AVA responses. Layer-dependent Biot-Gassmann analysis shows significant sensitivity of the P-wave velocity and density to fluid substitution, indicating that presence of light saturating fluids clearly affects the elastic response of sands. Accordingly, AVA deterministic and stochastic inversions, which combine the advantages of AVA analysis with those of inversion, have provided quantitative information about the lateral continuity of the turbidite reservoirs based on the interpretation of inverted acoustic properties and fluid-sensitive modulus attributes (P-Impedance, S-Impedance, density, and LambdaRho, in the case of deterministic inversion; and P-velocity, S-velocity, density, and lithotype (sand-shale) distributions, in the case of stochastic inversion).

The quantitative use of rock/fluid information through AVA seismic data, coupled with the implementation of co-simulation via lithotype-dependent multidimensional joint probability distributions of acoustic/petrophysical properties, provides accurate 3D models of petrophysical properties such as porosity, permeability, and water saturation. Pre-stack stochastic inversion provides more realistic and higher-resolution results than those obtained from analogous deterministic techniques. Furthermore, 3D petrophysical models can be more accurately co-simulated from AVA stochastic inversion results. By combining AVA sensitivity analysis techniques with pre-stack stochastic inversion, geologic data, and awareness of inversion pitfalls, it is possible to substantially reduce the risk in exploration and development of conventional and non-conventional reservoirs.

From the final integration of deterministic and stochastic inversion results with depositional models and analogous examples, the M-series reservoirs have been interpreted as stacked terminal turbidite lobes within an overall fan complex (the Miocene MCAVLU Submarine Fan System); this interpretation is consistent with previous core data interpretations and regional stratigraphic/depositional studies.

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DEFINING THE NORTHEASTERN BOUNDARY OF THE SUPERGIANT MARACAIBO FORELAND BASIN, VENEZUELA

David Rafael Contreras, MS

The University of Texas at Austin, 2008

Supervisor: Paul Mann

184 pages, 94 references, 3 tables

Differences in styles of structure and sedimentation and the distribution of hydrocarbons across the 140-km-long and 1-km-wide Burro Negro fault zone (BNFZ) constrain its origin as a deeply-rooted, right-lateral strike-slip fault that formed a major Paleogene tectonic and paleogeographic boundary along the northeastern edge of the supergiant Maracaibo basin. Complex subsurface structures and the lack of high quality seismic data and deep wells have made it difficult for previous workers to determine whether the BNFZ truncates the northeastern extension of the giant Eocene oil reservoirs in the Lake Maracaibo area or whether these reservoirs extend northeast of the BNFZ.

In Chapter 2, I integrate 2848 km of two dimensional (2D) seismic reflection data, 29 wells, gravity and magnetic data, and maps of outcrop geology to provide an improved structural interpretation of the BNFZ that can be used to assist future exploration programs in the region. Across the 1-km-wide BNFZ, the structural style seen on seismic lines changes abruptly from Eocene transtensional deformation in the Outer Maracaibo foreland basin to convergent deformation of the deepwater Inner Maracaibo foreland basin northeast of the BNFZ. I determined a right-lateral strike-slip fault character for the BNFZ that formed as a result of at least 7.2 km of Eocene right-lateral offset. Stratigraphic correlations using wells and seismic data spanning the BNFZ support the idea that giant Eocene oil reservoirs of the Lake Maracaibo area may continue towards the northeast into a complexly deformed Inner Maracaibo foreland basin consisting of Eocene deep-water sedimentary rocks. Late Eocene growth strata composed of deep-marine clastic rocks of the Agua Negra Group were deposited in piggyback basins in the Inner basin and accompanied Eocene thrusting and folding of the Lara nappes to the southeast

In Chapter 3, I present a subsurface geological interpretation of the subsurface of the northern edge of the Maracaibo foreland basin using 988 km of seismic data, 17 wells and 14,700 km2 of gravity and aeromagnetic data in the North Ambrosio area. Mapping of key surfaces in the basin that include the Eocene unconformity show that the primary structures in the subsurface are five, north to northeast-striking, right-lateral strike-slip faults of Eocene age (Icotea, East Urdaneta, West Urdaneta, San Ramón and La Concepción). On seismic data, these faults exhibit profiles typical of “positive flower zones”, where the strike-slip fault converges from a 2 to 4-km-wide fault zone at the surface to a narrow zone at the top of basement. The higher levels of the faults are composed of en echelon anticlines that form excellent structural traps for oil and gas. The 180 km2 Santa Rita pull-apart basin of Eocene age was identified at a left-step between the Icotea and East Urdaneta faults. Well logs show that Eocene sand bars were deposited in a tide-dominated deltaic system similar to that described by previous workers in areas to the south. I used temperature measurements from one well to calculate the depth of the oil window in the North Ambrosio area from 2.0 to 3.5 km and the gas window from 3.5 to 4.5 km. I also estimated the depth range of the “Golden Zone”, or depth interval where oil and gas is most likely to be preserved. The predicted Golden Zone corresponds well with reported depths of production and shows in the North Ambrosio area.

Gas potential for the North Ambrosio area could be determined form seismic and well data within a small area ~1800 km2 representing about 3.6% of the area of the Maracaibo foreland basin. The interaction of northeast-striking faults, such as the Icotea, East Urdaneta, West Urdaneta, and La Concepción fault zones controlled sedimentation during the Eocene foreland phase of the Maracaibo basin. Elongate Eocene sand bodies deposited in a tide-dominated deltaic system represent the main target for further exploration in the North Ambrosio area. The petroleum system is characterized by a strong foreland subsidence during Paleocene-Eocene times that buried Late Cretaceous source rocks of the La Luna Formation to depths of 4000 m below the surface. The source rocks reached gas generation window during two separate periods: middle-late Eocene and Miocene-Pliocene.

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SOIL FORMATION AND EROSION IN CENTRAL TEXAS: INSIGHTS FROM RELICT SOILS AND CAVE DEPOSITS

Mary Jennifer Cooke, Ph.D.

The University of Texas at Austin, 2005

Supervisors: Libby Stern and Jay Banner

Cave deposits containing sediments of eroded soils and relict soils preserved on modern uplands provide some of the few insights into understanding the Quaternary evolution of central Texas landscapes and environments. This study investigates an ancient soil-erosion event on the Edwards Plateau of central Texas by using a new approach that relies on the strontium isotope composition of the ancient soil as an indicator of ancient soil thickness. I found the strontium isotope composition of soil on the Edwards Plateau today varies with soil thickness. I also found that variations in strontium isotope compositions of fossil plants and animals provide a record of temporal changes in soil thickness. Furthermore, I present stable carbon, oxygen, and nitrogen isotope data measured on sediments and fossils from a central Texas cave-fill deposit that support the hypothesis that increases in aridity and increases in precipitation intensity may have facilitated massive, late Quaternary soil erosion on the Edwards Plateau.

The origin of the former thick soil cover that was removed by the erosion is poorly understood. This study uses the geographic distribution and the textural and mineralogical properties of relict thick soils along with their neodymium isotope compositions, and rare earth element concentrations to determine the silicate source of the former thick soils. I propose that the Del Rio Clay, a locally-eroded, stratigraphically-higher, clay-rich strata provided the silicates to form thick soils overlying the silicate-pure Edwards Limestone.

Four important conclusions of this study are that: 1) in areas where the soil and bedrock are distinct in their strontium isotope composition, the strontium isotope composition of the soil varies with soil thickness, 2) the strontium isotope composition of terrestrial fossils can be a useful tool to reconstruct temporal changes in soil thickness, 3) climate variability can facilitate massive soil erosion with regional environmental consequences, and 4) soil formation from now-eroded bedrock of a higher stratigraphic unit may be more common than previously recognized. Thus, in light of future changes in climate and land use, soil conservation strategies should be considered in regions where soils rest on relatively pure limestones, because they are likely a “non-renewable” resource.

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STRUCTURAL ANALYSIS OF THE SAN SIMEON FAULT ZONE, CALIFORNIA: IMPLICATIONS FOR TRANSFORM TECTONICS

Ryan Thomas Coppersmith, M.S. GeoSci

The University of Texas at Austin, 2008

Supervisor: Mark Cloos

The San Gregorio-Hosgri fault zone (SGH), located in the Southern Coast Ranges of California is a 420 kilometer long right-lateral strand of the San Andreas fault system. The San Simeon fault zone is a segment of the SGH that cross-cuts the Nacimiento block which is primarily composed of Franciscan Complex accretionary prism. The Nacimiento block is juxtaposed against the Salinian block, a portion of the Sierra Nevada batholith, by the Nacimiento Fault. The Nacimiento and Salinian blocks have been displaced from the south in a right lateral sense as part of movements within the San Andreas fault system. The San Simeon segment juxtaposes mid-Jurassic Coast Range Ophiolite with Cretaceous Franciscan accretionary prism material. These units are locally overlain by the Oligocene Lospe Formation and Miocene Monterey Formation.

To better understand the movement history near the San Simeon fault zone, 33 kilometers of outcrop were examined along the sea-cliff between Ragged Point in the north and Pico Creek to the south. Of this transect, 4 kilometers were buried under marine terrace and sand dunes. No data was collected along 1 kilometer of transect due to the presence of elephant seals. The 28 kilometers of bedrock examined include: 7 kilometers of ophiolitic material, 16 kilometers of Franciscan Complex, 2 kilometers of Lospe Formation, and 3 kilometers of Monterey Formation. In all, 466 minor faults and 254 major (≥0.5 meters exposure length) faults were mapped, and 22 of these major faults juxtapose different formations (n=8) or different units within the ophiolite (n=14). Slickenlines were measured on 517 faults, of which 237 record sense of slip. Of the faults measured, 199 are strike-slip (0-30°rake), 179 are dip-slip (60-90°rake), and 139 are oblique-slip (31-59°rake). Sense of slip indicators record a wide range of movements: 49 right-lateral, 47 left-lateral, 40 normal, 38 reverse, 18 reverse left-lateral, 17 normal left-lateral, 15 normal right-lateral and 13 reverse right-lateral faults.

The study transect was divided into structural domains based on fault kinematic patterns. Movement recorded in these data resulted from transform-related faulting. Fault kinematics that differ from the regional N35W strike of the San Simeon fault zone are explained by local variations in movement patterns near the San Simeon fault zone. This variations include local bends and splays off of the fault zone. The Lospe and Monterey Formations that make up 18% of the mapped transect contain 12% of the faults. These formations only experienced transform-related deformation. Faults in the Monterey Formation are parallel to the regional San Simeon fault zone. Faults in the Lospe Formation to the north primarily strike E-W. Ophiolite material contains 25% of the mapped transect and 37% of the faults. These faults primarily indicate right-lateral movement; however, reverse and normal faulting near perpendicular to the regional NW fault trend is common. The Franciscan Complex along 57% of the mapped transect contains 51% of the faults. Faults in the Franciscan Complex and the ophiolite potentially record subduction-related faulting, but evidence from fault kinematics from this study indicates transform-related faulting. Reverse and right-lateral faulting along the splays is indicated. East of San Simeon Point, a 1 kilometer wide San Simeon fault zone is indicated by a cluster of faults between the San Simeon Pier and Broken Bridge Creek, the eastern boundary of the fault zone. The complexity of fault patterns and kinematics in and near the San Simeon fault zone record a long and complex history of transform faulting.

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THE ORIGIN OF PARTIAL-DISEQUILIBRIUM MAJOR- AND TRACE-ELEMENT ZONING IN GARNETS FROM THE PICURIS MOUNTAINS, NM

Wesley Dean Crawford, Jr., M.S.

The University of Texas at Austin , 2008

Supervisor: William D. Carlson

189 pages, 31 references, 2 tables

New evidence from X-ray mapping, quantitative major- and trace-element analyses, and garnet-inclusion suites suggests that the disequilibrium behavior in garnets from the Picuris Mountains, NM, is the result of changes in matrix assemblages at a very local scale (i.e., within the immediate vicinity of each growing porphyroblast). In addition, detailed petrologic study of metapelites with a range of bulk compositions reveals a wide variety of partial-disequilibrium garnet zoning patterns not previously known to exist. The complicated zoning patterns of garnets from samples containing the assemblage garnet + biotite + muscovite + quartz + plagioclase can be explained by a local change from a garnet-forming to a garnet- and biotite-forming reaction, coupled with the breakdown of allanite, the nucleation of apatite and monazite, and the temporary presence of xenotime. This interpretation is supported by mass-balance calculations that show that the breakdown of less than one modal percent allanite could supply the spikes in trace-element concentration observed in garnet. This study also provides plausible explanations for the unexpected zoning patterns found in garnet-staurolite schists and one calc-schist. The implications for petrologists of cryptic disequilibrium like that recorded by garnets of the Picuris Range are many fold. In particular, the incautious application of geothermometers and geobarometers, especially those which utilize accessory minerals, could lead to seriously flawed results.

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STRUCTURAL AND SEQUENCE STRATIGRAPHIC ARCHITECTURE OF THE TERTIARY SECTION IN THE RED FISH BAY AREA OF TEXAS

Luis Arturo Crespo, MA

The University of Texas at Austin , 2006

Supervisor: William L. Fisher & Robert G. Loucks

The main objective of this report is to describe the structural and sequence stratigraphic architecture of the Tertiary section in the Red Fish Bay area of Texas . The report was based upon previous investigations of the Tertiary section carried out in the Red Fish Bay subbasin area.

A high influx of sediments coupled with relative sea-level changes produces a thick sedimentary section in the Red Fish Bay area composed of deep- to shallow-water deposits. At a time of a third-order lowstand, river systems incising into the older shelf strata transported sediment beyond the shelf edge to accumulate on the slope and subbasin floor. The loading stress of these third-order deposits caused instability in the underlying muds of the older Vicksburg and Frio Formations and a growth fault was initiated. Deposition of the lower Frio unit continued to take place in the subbasin, and as the underlying mud migrated, the hanging wall of the growth fault underwent rotation and a shale ridge formed at the most basinward edge of the subbasin. Additionally, two minor growth faults activated which subdivided the Lower Frio unit of the subbasin into three “minibasins” which all have similar fourth- and higher-order systems tracts and are also chronostratigraphically correlative from one to the other. The long-term second-order lowstand systems tract ended, marked by the top of the Lower Frio unit and a long-term second-order transgressive systems tract began as indicated by the deposition of the middle to upper Frio and Anahuac units. The second-order transgressive systems tract contains significantly thick higher order transgressive and highstand systems tracts. A succeeding long-term second-order highstand systems tract continued through the remainder of the Anahuac , the Oakville Formation and passed the age range of this report. During this second-order highstand systems tract, well-log data and seismic data indicate the development of lowstand incised valleys in the Oakville Formation.

By interpreting and constructing the structural and sequence stratigraphic architecture of this area, the prediction of sand (and other reservoir rock) distribution can be improved. Applying correct interpretation models and techniques, as well as correlation tools such as the Site-Specific Sequence-Stratigraphic Section (S 5 ) benchmark composite log, erroneous correlations which could produce the wrong stratigraphic and structural architecture can be avoided.

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SUBGLACIAL WEST ANTARCTIC VOLCANOES DEFINED BY AEROGEOPHYSICAL DATA AND THE POTENTIAL FOR ASSOCIATED HYDROTHERMAL SYSTEMS

Hunter-West Anderson Danque, M.S. Geo. Sci.

The University of Texas at Austin, 2008

Supervisor: Donald D. Blankenship

112 pages, 124 references, 3 tables

Subglacial hydrothermal systems beneath the West Antarctic Ice Sheet (WAIS) are important objects of research because meltwater associated with them can act as a lubricant beneath this potentially unstable ice sheet. In addition, subglacial hydrothermal systems on Earth may provide analogues for subglacial microbial habitats under the polar caps of Mars or other icy bodies. The West Antarctic subglacial volcanoes compared herein display a range of plausible hydrothermal systems. One end-member is Mt. CASERTZ which is a recently erupted subglacial volcano discovered in the early 1990's just upstream of a well lubricated ice stream. It sustains a depression in the ice surface, and it is associated with nearby subglacial lakes. Therefore, it has a high potential for sustaining a short-lived hydrothermal system. At the other end of the spectrum of plausible subglacial hydrothermal systems is a subglacial volcano, designated M, which appears to be inactive and to possess no substantial hydrothermal system. In the middle of the spectrum is a subglacial volcano, designated L, which lies near the ice divide between the Ross Sea and Amundsen Sea Embayments in West Antarctica. It has a well-defined intrusive body and a terraced morphology consistent with multiple eruptions. Subglacial Volcano L is distinctly larger than the other two volcanoes, and it is probably a greater heat source than M while being older than Mt. CASERTZ. Using newly developed radar techniques, I observed that Volcano L has several small (200-500 meter) subglacial lakes located over and on the boundaries of the modeled underlying intrusive body implying the intrusive body is associated with subglacial melting. Adjacent to volcano L, I also observed a large drawdown (designated H) in the internal layers of the ice sheet consistent with substantial basal melting. To better evaluate ice mass loss associated with anomaly H and Volcano L, I developed an algorithm that maps anticorrelations between internal layers within an ice sheet and subglacial topography. Using this algorithm, I discovered that the layer drawdown adjacent to L extended along a highly linear zone about 28 kilometers in length. The layer drawdown near Volcano L implies a mass loss at the base of the ice sheet of 25 cubic kilometers. This mass flux can be explained by localized subglacial melting associated with igneous processes. If the mass flux is due to local subglacial melting, then subglacial lakes identified on either side of the drawdown are hydraulically plausible destinations for the meltwater. I hypothesize that the linear zone associated with anomaly H is a fault supplying an avenue for the movement of magma to the base of the ice sheet that supports an associated hydrothermal system. Together these factors make the subglacial lakes that I have observed on Volcano L and adjacent to the hypothesized fault highly attractive targets for geochemical and biological sampling of a mature subglacial hydrothermal system.

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HYDROGEOLOGICAL CHARACTERIZATION OF BASEFLOW TO JACOB’S WELL SPRING, HAYS COUNTY, TEXAS

Sarah Cain Davidson, M.S.Geo.Sci.

The University of Texas at Austin, 2008

Supervisor: Philip C. Bennett

Jacob’s Well is a karst spring that discharges from the Trinity aquifer in central Texas. Ongoing development and increased groundwater pumping in the area around the spring are thought to be impacting the volume of discharge at the spring—however, the source of spring discharge is poorly understood. The goals of this study are to characterize the chemistry of springflow and nearby surface waters and groundwaters and to identify the source or sources of water that contribute flow to the spring under low flow conditions.

The spring is located in the Middle Trinity aquifer within the Lower Cretaceous Trinity Group in central Texas. The Trinity Group is composed of alternating terrestrial and marine deposits, with most groundwater flow occurring through secondary porosity in the carbonate units. The cave leading up to the spring consists of at least two water-filled conduits that have been mapped down into the Cow Creek Limestone and several hundred meters to the north and northwest of the spring outlet.

Water samples and measurements of water levels and chemical field parameters were collected at 48 study sites representing stream, spring, and well waters over a 250-km2 area around the spring from May–September 2008. The area was in drought throughout this period and the results thus represent low flow conditions. Samples were analyzed for major and trace ions, organic and inorganic carbon, and isotopes of O, H, and Sr. Modeling using PHREEQC was used to calculate whether realistic phase changes in known aquifer minerals could explain the chemical differences between sampled waters along hypothesized flowpaths.

Water levels indicate that groundwater flows generally to the southeast within the study area. Chemical analyses of water samples show three chemical types: (1) Ca-Mg-HCO3 waters, which make up all spring water, all surface water, and most ground water samples; (2) high TDS Ca-Mg-SO4 ground waters; and (3) high TDS Na-Mg-Ca-SO4 ground waters. Measured element concentrations, strontium isotope data, and geochemical modeling results indicate that the high TDS waters most likely come from the upper member of the Glen Rose Limestone downgradient from the spring (type 2) and from the Hosston Formation in the Lower Trinity aquifer (type 3).

Physical and chemical properties of the sampled waters were used to define which well and stream samples might represent water within the area contributing to baseflow at the spring. Water samples taken from seven sites north and west of the spring were found to represent possible sources of springflow during the study period. These findings suggest the possibility of two distinct flowpaths connecting the aquifer to Jacob’s Well: (1) flow to the southeast within the Cypress Creek watershed along the regional groundwater flow path estimated from water level measurements, and (2) flow to the east along fracture or conduit paths that cross the surface divide between the Upper Blanco River and Cypress Creek watersheds.

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COMPLEX STRUCTURAL AND FLUID FLOW EVOLUTION ALONG THE GRENVILLE FRONT, TRANS-PECOS TEXAS

Benjamin R Davis, M. S. Geo. Sci.

The University of Texas at Austin, 2007

Supervisor: Sharon Mosher

A narrow (~7 km wide) fold and thrust belt in west Texas that represents the northernmost extent of the Grenville collision belt along the southern margin ofLaurentia (Grenville Front) records a complex history of deformation and fluid flow. The main Streeruwitz thrust that emplaced -1.35 Ga high-grade metamorphic rocks over -1.25 Ga foreland sedimentary and volcanic rocks postdates polyphase deformation in the footwall and is itself complexly folded into local domes and basins. Deformation can be characterized by four stress regimes. A pre-Streeruwitz ductile deformation phase, dextral oblique strike-slip motion, deformation associated with Streeruwitz thrusting, and formation of complex domes and basins resulting from continual transpression. Fluids with an evolving chemistry were channelized along the thrusts, metasomatically altering the adjacent rocks.

Deformation consisting of six phases of folding, metasomatic reactions, and veining within foreland rocks record a change in kinematics and evolving fluid chemistry with time. An early phase of siliceous fluids during D2 caused replacement of mafic dikes and dolostones that preserve fi/s] and formation of extensive talc lenses aligned axial planar to F2, forming the dominant 82. Subsequent upright vertical sheath folds, F4, indicate dextral oblique motion on high-angle west-northwest-trending faults. The Streeruwitz thrust and subsidiary imbricate thrusts truncate Fi-F4 folds at a high angle requiring a change in the overall kinematics of the deformation. Late chevron to box folds and kinks of 82 are generally associated with shears locally related to thrusting. Initial thrusting at depth produced mylonites in both footwall (syn-S2) and hanging wall rocks that were later brecciated in the final stage of thrusting along the Streeruwitz. Further evolution of fluids along the thrusts is recorded in the breccias and veins, starting with siliceous- and alkali-rich fluids. Lastly, carbonate-rich fluids replaced footwall rocks and cemented breccias in both the hanging and footwalls. Final deformation of the area folded the Streeruwitz and imbricate thrust sheets into complex domes and basins trending SW and SE.

The degree of structural complexity and fluid flow interaction requires a new kinematic model for the southern margin of Laurentia, one where a north-verging indenter collided with southern Laurentia and then under went clockwise rotation. The disparity in timing of deformation, and of kinematics, between west Texas and the Llano uplift of central Texas requires active subduction in west Texas after collision in central Texas. Furthermore, the complex structural histories and differences in kinematics with time between the hanging wall and the footwall of the Streeruwitz thrust can be explained by clockwise rotation of an indenting continent after docking on southern Laurentia.

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SUBGLACIAL MORPHOLOGY AND STRUCTURAL GEOLOGY IN THE SOUTHERN TRANSANTARCTIC MOUNTAINS FROM AIRBORNE GEOPHYSICS

Marcy Brooke Davis, MSGeoSci

The University of Texas at Austin, 2001

Co-Supervisors: Donald D. Blankenship and Ian W. D. Dalziel

The Transantarctic Mountains (TAM) form the high western rift flank of the West Antarctic Rift System (WARS), a region of extended crust that separates East and West Antarctica. Little is known about the structural geology in the southern TAM due to limited accessibility and more ice cover than in the central and northern TAM. The objectives of this study are to characterize the subglacial bedrock morphology interior of the southern TAM and to define the structural geology along the southern TAM Front through analysis of airborne ice-penetrating radar data.
The airborne survey extended from the Ross Ice Shelf, southward over the TAM along the 150ºW meridian and between the Scott and Reedy Glaciers then over the high plateau and through the South Pole. Approximately 15,000 line km were flown and processed using finite difference migration techniques in a seismic processing software package. Subsequently, the ice and bed surfaces were picked along each line and known geology was interpreted on the radar records where it exists. Ice-penetrating radar sounding coupled with a compilation of field geologic studies has proven to be a powerful technique for examining the architecture and structural geological relationships of the southern TAM.

Four distinct morphological provinces are identified along the length of the survey, these include: 1) the South Pole Basin and Plateau Province, with low relief features and up to 4 km of ice; 2) the Alpine Glaciated Province, with well-preserved U-shaped valleys that show a glaciation network that flowed opposite of contemporary glaciers; 3) the TAM Massif, which includes three subglacial blocks and the outcropping portion of the TAM; and 4) the TAM Front, a normal fault zone north of the TAM to Ice Stream A.

The southern TAM have a southward tilted block structure with the area of maximum uplift in a region 30-50 km wide from the Watson Escarpment, the highest part of the TAM in this area, southward and is bounded by NW-SE-trending normal faults on both the north and south sides. Down-to-the-north normal faults north of the Watson Escarpment topographically downdrop the TAM from >3000 m to sea level over ~50 km and facilitate the development of the Leverett Glacier and Ice Stream A. The primary structural trend between the Scott and Reedy Glaciers is NW-SE, parallel to the TAM. Faults oriented obliquely to the TAM break the area of maximum uplift into three NNW-SSE trending blocks that appear offset ~10 km in a left-lateral sense relative to each other with range-parallel horst and graben features superimposed. One of these faults may control the eastern side of Scott Glacier. Structural relationships across the Watson Escarpment suggest that the southern TAM are a result of upward block faulting along the TAM Front rather than a result of regional upwarping.

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THE TECTONICS OF TRANQUITAS: A FIELD STUDY OF RIFT THROUGH PASSIVE MARGIN DEVELOPMENT AND LARAMIDE DEFORMATION IN TRIASSIC AND JURASSIC STRATA OF THE SIERRA MADRE ORIENTAL, NE MEXICO

Matthew H. Davis

The University of Texas at Austin, 2005

Supervisor: Randall Marrett

Exposed near Galeana, Nuevo Leon are sedimentary deposits and contemporaneous structures that record the rifting and opening of the Gulf of Mexico, passive-margin development, and Laramide compression in the region. A mapping, sedimentologic, and structural study utilizing thin sections, measured sections, aerial photos and kinematics has produced a detailed stratigraphic section that records the transition from terrestrial to open-marine deposition and the orientation and timing of deformational events. Triassic to Early Jurassic red beds in the Huizachal Group are composed of fluvial and marine sands. The La Boca and La Joya Formations, respectively, are separated by a polymictic cobble conglomerate. The Callovian Minas Viejas represents the initial stages of marine transgression and the overlying interbedded carbonates and evaporites of the Zuloaga and Olvido Formations respond to cyclic eustatic sea-level fluxuations. The increase of biodiversity through the upper Jurassic strata reflects a change from restricted to open-marine conditions. Rift-related tectonics and gravity driven brittle extension features within the carbonates have been overprinted by Laramide orogenesis. The red beds have been folded and faulted into a broad Laramide anticlinorium with smaller intrusion cored folds having amplitudes on the order of 10's of meters. Within the evaporite lies the decollement for Laramide thin-skinned deformation, thus there is a high degree of structural complexity represented in the overlying carbonates as tight folding patterns. By integrating concepts of depositional systems with structural deformation the hypothesis, “There is an exhumed preraft block in the Zuloaga Limestone around San Pablo de Tranquitas.” will be tested.

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STRATIGRAPHIC EVOLUTION AND FACIES ANALYSIS IN A PALEOCENE REEF MOUND, LA POPA

BASIN, NORTHEAST MEXICO

Jose Francisco Delgado Gutierrez, MS Geo. Sci.

The University of Texas at Austin, 2003

Supervisor: William L. Fisher for R. K. Goldhammer (Deceased)

111 pages, 65 references, color illustrations, CD-Rom

The Paleocene La Popa reef mound is an isolated carbonate platform exposed in the foot-wall of the La Popa salt-weld structure within the Late Cretaceous- Paleocene La Popa Salt Basin (northeast Mexico). A facies and sequence stratigraphic analysis was undertaken to define the three-dimensional geometry, facies architecture and the stratigraphic development of this world class, 3-D exposure of a Paleocene reef mound.

Microfacies analysis was performed with more than 240 hand samples and 91 thin sections from 12 stratigraphic sections using the methodology described by Flügel (1982) & Carozzi (1988). The results indicate that the La Popa reef mound is composed mainly of calcareous algae (Dasycladaceae and coralline red algae) and they reveal the significance of these types of organisms as the primary reef builders of Tertiary reefs, rather than corals. Microfacies analysis also indicates that windward-leeward effects played a major role in defining the facies architecture.

The facies architecture of the Reef Mound reveals a classic facies zonation similar to the modern-day coral-algal reefs, with the Paleocene facies tracts defined by depth-dependent green and red algae. In the mixed clastic-carbonate section (The La Popa Prow), 1-D stacking-pattern analysis and the facies proportions were performed between the clastics and carbonates to develop a hierarchical subdivision of the genetic units defined by: the fundamental cycle, the cycle sets, the high-frequency sequences and the second-order super sequences. In this unit, each sequence element regardless of scale (for example the fundamental cycle, or the high-frequency sequence, or the second-order supersequence) the TST tends to consist of clastic sediments and the HST consists of carbonate sediments.

1-D and 2-D stacking pattern analysis were conducted in the Tertiary part of the succession (the platform-top canyon sections), which is Paleocene in age and consists of one second-order supersequence defined by higher-frequency elements. In this unit the genetic packages consist of an amalgamation of the fundamental cycles and cycle sets within the Reef Mound.

The termination or drowning sequence consists of a second-order supersequence boundary, and corresponds to the position of "stratigraphic reversal" where the shallow-water reef mound top starts to drown in response to local (salt-induced subsidence?) or regional (eustatic?) accommodation increase.

The major phase of "reef mound" development is linked to the HST of a second-order supersequence, and the buildup termination occurs through drowning during the TST of a subsequent second-order supersequence.

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TRAVERTINE DEPOSITS AS RECORDS OF GROUNDWATER EVOLUTION IN URBANIZING ENVIRONMENTS

Laura Michelle DeMott, M.S.Geo.Sci

The University of Texas at Austin, 2007

Supervisor: Jay L. Banner

Urban development has multiple impacts on groundwater, including changes in patterns of recharge, alteration of groundwater flow paths, and increased water contamination. For the most part, these impacts have only recently begun to be appreciated, and in most aquifers there is a lack of data available on recharge and water quality prior to urbanization for comparison. This lack of data across the period of urbanization makes the prediction of the impacts of future development difficult. I propose that recently deposited spring water calcite (travertine) may provide a proxy record of changing groundwater composition over time. The city of Austin, Texas has undergone a large increase in urbanization over the past 40 years. Because the chemistry of municipal water in Austin is distinctive from the local groundwater, I have examined the possibility that the amount of urban water input to local groundwater recharge can be assessed using the isotopic composition of strontium ( 87 Sr/ 86 Sr) in combination with elemental concentrations and ratios of Mg/Ca and Sr/Ca. This study examines the current depositional environment of three travertine-depositing springs in the Austin area. It makes use of the modern system, including experimental growth of calcite on artificial substrates in the springs, to interpret a 30-year temporal record provided by one of the three studied springs.

Three travertine-depositing springs were studied over the course of one year to examine water chemistry and strontium isotope composition changes on a seasonal basis. Elemental concentrations and strontium isotope ratios remained fairly constant throughout the study year, and showed the influence of urban water in the isotopic compositions of the spring water. Glass plate substrates were employed over a four-month time period, to examine monthly changes in travertine growth and isotopic and elemental compositions. Using these substrate experiments, I determine travertine growth rates and effective trace element partition coefficients. These partition coefficients are higher than values determined from laboratory experiments from the literature, indicating that partitioning behavior in natural systems may be different than that of controlled laboratory experiments. Applying these partition coefficients to the travertine temporal record provides a more accurate interpretation of past water compositions. Comparison of stable isotopes of carbon and oxygen between spring waters and plate calcites revealed that the plate carbonates (travertines) are not forming in isotopic equilibrium with their dripwaters. Based on this, interpretation of stable isotope records from these travertines should be treated with caution.

Isotopic and elemental analyses were conducted on a spring-fed travertine that preserved 30 years of deposition on a roadcut through Lower Cretaceous marine limestones. The spring is actively precipitating calcite, and appears to have grown continually since the excavation of the roadcut. The contributing area to this spring has undergone an increase in urban land use of approximately 40% since 1983. 87 Sr/ 86 Sr data for the travertine and spring waters show a small but resolvable increase over time, from 0.70790 to 0.70797. These values for 87 Sr/ 86 Sr are higher than those for Lower Cretaceous marine limestones, and lower than values for municipal water as well as soil exchangeable Sr. The increase in 87 Sr/ 86 Sr may be accounted for in three ways: 1) Through an increased relative proportion of municipal water input to the groundwater in the spring's contributing area; 2) Through increased overall recharge in the area, resulting in more water-soil interaction; or 3) A combination of the two. Modeling of karst flow processes (water-limestone interaction and fluid mixing) shows that the trend in elemental ratios and 87 Sr/ 86 Sr may be accounted for by processes of soil water-limestone interaction and mixing with urban waters. Models also indicate that this fluid mixing likely occurs in the epikarst zone, and that urban water may account for as much as 80% of the discharge from the spring. Values for 87 Sr/ 86 Sr in spring waters are likely dampened by limestone interaction during times of low recharge. This model of water-limestone interaction and urban water mixing implies that urbanization in this particular area resulted in increased recharge and that this recharge may be quantifiable over time. Travertine proxies represent a previously unused resource for examining urban recharge in karst terrains.

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ORIGIN OF A COMPLEX DUNE PATTERN, ALGODONES, SOUTHEASTERN CALIFORNIA

Dana C. Derickson, M.S. Geo. Sci.

The University of Texas at Austin, 2005

Supervisor: Gary Kocurek

The Algodones dune field in southeastern California contains two unusual features which are cause for investigation. First, several different morphologies of sand dunes are situated within a relatively small area. Previous studies attribute this complexity to the dunes themselves, which modify the wind within the dune field, allowing different types of dunes to coexist in equilibrium. Yet this hypothesis has never really been proven. A different approach would be to consider the dunes as a pattern, and a complex pattern would be explained as simple patterns superimposed on each other. Each simple pattern would then correspond to a different generation of dunes.

Pattern analysis of the Algodones revealed two different generations of dunes within the dune field. The longer, more widely spaced dunes correspond to the compound crescentic dunes in the central portion of the dune field. The second generation includes the remaining morphologies, which are all interrelated. The arms of crescentic dunes can elongate and become linear dunes, and examples of this can be seen in the northern end of the dune field. Superimposed crescentic dunes have shorter crest lengths and spacings than the simple crescentic dunes because of sorter development time. Their location on the stoss on the stoss slopes of the compound crescentic dunes means that they are subject to avalanching over the lee slopes of these dunes. Their average orientations are different because the superimposed crescentic dunes are subject to secondary flow from the lee faces of the compound crescentic dunes. Zibars in the western edge of the dune field correspond to coarse-grained sediment.

The second unusual feature of the Algodones is the 400 m wide, 40 m thick topographic ramp located along the western margin of the dunefield. One or two more ramps exist east of the western margin, and each ramp is capped by a linear dune. Sweet et al. (1988) postulated that the westernmost ramp was the trailing margin of an eastward migrating dunefield. Ground penetrating radar (GPR) profiles along the western margin of the dunefield have contradicted this model. The subsurface cross-strata and surface topography are more consistent to that of migrating compound dunes. Whether these dunes are of the same age, or part of a transgressive dunefield system migrating from paleolake shorelines, the source of the dune sand, is yet to be proven. However, the intermittent nature of Lake Cahuilla and linear trends within the dune field support the hypothesis that the ramp is part of a transgressive dune field.

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STRUCTURAL ANALYSIS IN THE COAST RANGE OPHIOLITE NEAR PASKENTA, CALIFORNIA: IMPLICATIONS FOR TECTONIC UPLIFT PROCESSES

Andrew David Dewhurst, M.S. Geo. Sci.

The University of Texas at Austin, 2008

Supervisor: Mark Cloos

220 pages, 85 references, 4 tables

California has been a site of subduction since about 155 Ma. The Franciscan complex accumulated in front of, and beneath, the crystalline leading edge of the North American Plate: a belt of oceanic crust and mantle known as the Coast Range Ophiolite. Near Paskenta, California, the blueschist facies Franciscan rocks (South Fork Mountain Schist) are juxtaposed against the ophiolitic rocks along the Coast Range Fault. These Franciscan rocks have risen ~15 km and the ophiolitic rocks at least 3 km and perhaps as much as 10 km. The intervening Coast Range Fault has a near vertical dip. It has previously been interpreted as a rotated east-dipping thrust fault that formed by subduction underthrusting, an east-dipping décollement to a series of out-of-sequence imbricated thrusts, and a high-angle west-dipping reverse fault that formed by collisional overthrusting. To explain the unroofing of the Franciscan rocks, it has been interpreted as a high-angle normal fault. Notably, fault-related kinematic data in support of tectonic models for Coast Range Fault movement and ophiolite emplacement are sparse.

To constrain the geometry and kinematics of the Coast Range Fault and ophiolite emplacement, three geologic transects were made along sinuous roads near Paskenta. Approximately 30 km of roadcut is present along the ~60 km length of road. Exposures are typically less than two meters high, but locally as tall as 20 m, along roadcuts that extend for tens to a few hundred meters. Lithologies were mapped in the roadcut exposures and the attitudes of fault planes and direction and sense of slip was measured. Data were obtained on 275 faults traceable for ≥ meter. Within serpentinite shear zones, the attitudes of 1159 minor faults were measured.

Mapping revealed that although all parts of the ophiolite suite are present near Paskenta, the pieces are well shuffled. For example, slabs of layered radiolarian chert are found in the western part of the ophiolite near the Franciscan rocks and masses of serpentinite are present in the eastern part near the steeply eastwards dipping strata of the depositionally overlying Great Valley Group (Knoxville Formation). In addition, faults and serpentinite shear zones are heterogeneously distributed. In the Paskenta area, the ophiolite is not simply an upturned slab of oceanic crust. It is well described as an ophiolitic mélange. Stereographic analysis reveals the pattern of faulting along each transect is similar with most faults striking roughly north-south and steeply dipping - near-parallel to the Coast Range Fault. For major faults with full kinematic observations, normal offsets (n = 226) dominate over those with reverse offset (n = 97). Movement patterns recorded in the minor faults found in the serpentinite shear zones are less defined, but overall patterns appear similar.

Uplift of the Franciscan complex and Coast Range Ophiolite near Paskenta was accomplished not just by normal, near-vertical movement along the Coast Range Fault, but also by slip along the numerous faults and shear zones within the ophiolite belt. However, faulting associated with the ascent of Franciscan rock does not appear to be sufficient to account for the thorough disruption of the ophiolite terrane in this area. The ophiolitic mélange was probably generated prior to ophiolite emplacement in an oceanic transform setting.

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FRACTURE TECTONICS, FRACTURE POROSITY EVOLUTION AND STRUCTURAL DIAGENESIS, CAMBRIAN ERIBOLL SANDSTONES, NORTHWESTERN SCOTLAND

Kira Diaz-Tushman , M.S. Geo. Sci.

The University of Texas at Austin , 2007

Supervisors: Stephen E. Laubach & Sharon Mosher

Cambran Eriboll Sandstones in Northwestern Scotland contain 5 sets of regional fractures; Sets A through E. Set A strikes north to NNE, Set B strikes NW-WNW, Set C strikes NE, Set D strikes east, and Set E strikes north. Crosscutting relationships and orientations with respect to bedding places the relative ages as Set A being the oldest and Set E being the youngest, with sets B through D in between. Based on orientation and intensity patterns I interpret Set A to have formed in a platformal setting before emplacement of the Moine Thrust Zone (MTZ). Sets B and C were likely formed during and shortly after emplacement of the MTZ. Set D may have formed after thrust emplacement, possibly during Late Devonian or later regional extension. Set E was likely caused by late faulting in the Cenozoic.

Sets A and D are comparable, in the fact that both are likely formed in a basinal setting, with similar cement patterns and structures. Set A and Set D differ in amount of preserved fracture porosity. Both sets contain characteristic localized cement deposits (synkinematic bridges) having crack seal and lateral growth textures. Such bridges are common in sedimentary basins. Lander et al. (2002) explained bridges as a consequence of greatly differing quartz growth rates on broken (fast) and idiomorphic (slow) quartz surfaces. Bridges form where incremental opening allows growth on some grains to span the fracture between opening steps. Local cross-fracture bonding and subsequent rebreaking perpetuates localized fast growth. Set A is the first documented case where former voids between bridges are filled with massive quartz having no crack-seal texture. This pattern indicates that Set A is a basinal system fossilized by protracted burial. Growth rate experimental data (Lander et al., 2002), fluid-inclusion data I collected from synkinematic quartz, burial history, and the 1.6 cm aperture size of the largest fractures allows me to calculate the time needed to fill fractures with slow growing quartz in Sets A and D. Results agree with my fracture timing estimates based on orientation and kinematic compatibility arguments. My observations and sealing estimates also show that fractures can remain open for millions of years in deep basinal settings, where they are potential conduits for fluid flow. Because sets A and D have identical attributes to basinal fracture systems in economically important fractured hydrocarbon systems, such as tight gas sandstones, my fracture observations from the ~150 km long Eriboll Sandstone outcrop belt provide a rare view of regional fracture characteristics typical in the subsurface.

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GRAVITY ANALYSES FOR THE CRUSTAL STRUCTURE AND SUBGLACIAL GEOLOGY OF WEST ANTARCTICA, PARTICULARLY BENEATH THWAITES GLACIER

Theresa Marie Diehl, Ph.D.

The University of Texas, 2008

Supervisor: Donald D. Blankenship

209 pages, 162 references, 18 tables

The West Antarctic Ice Sheet (WAIS) is mostly grounded in broad, deep basins (down to 2.5 km below sea level) that are stretched between five crustal blocks. The geometry of the bedrock, being mostly below sea level, induces a fundamental instability in the WAIS through the possibility of runaway grounding line retreat. The crustal environment of the WAIS further influences the ice sheet’s fast flow through conditions at the ice-bedrock boundary. This study focuses on understanding the WAIS by examining the subglacial geology (such as volcanoes and sedimentary basins) at the ice-bedrock boundary and the continent’s deeper crustal structure- primarily using airborne gravity anomalies. The keystone of this study is a 2004-2005 aerogeophysical survey over one of the most negative mass balance glaciers on the continent: Thwaites Glacier (TG). The gravity anomalies derived from this dataset- as well as gravity-based modeling and spectral crustal boundary depth estimates- reveal a heterogeneous crustal environment beneath the glacier. The widespread Mesozoic rifting observed in the Ross Sea Embayment (RSE) of West Antarctica extends beneath TG, where the crust is ~27 km thick and cool. Adjacent to TG, spectrally-derived shallow Moho depths for the Marie Byrd Land (MBL) crustal block can be explained by thermal support from warm mantle. I assemble here new compilations of free-air and Bouguer gravity anomalies across West Antarctica (from both airborne and satellite datasets) and re-interpret the extents of West Antarctic crustal block and their boundaries with the rift system. Airy isostatic gravity anomalies reveal that TG is relatively sediment starved, in contrast to the sediment-rich RSE. TG’s fast flow velocities could be sustained in this sediment poor environment if higher heat flux in MBL was providing an ample source of subglacial melt water to the glacier. The isostatic anomalies also indicate that TG’s outlet rests on a bedrock sill that will impede future grounding line retreat (up to ~100 km) and temporarily stabilize the glacier.

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CHARACTERIZATION OF HISTORIC LIME MORTARS

Kara Rose Dotter, MSGeoSci

University of Texas , 2006

Supervisor: Kitty Milliken

Historic lime mortars are an amalgam of natural and man-made materials. Thus, the study of lime mortars inherently requires interdisciplinary approaches. In an effort to evaluate the applicability of select analytical techniques typically utilized by geoscientists, fourteen samples of historic lime mortars are examined with transmitted polarized light microscopy, scanning electron microscopy (SEM), backscattered-electron imaging (BSE), and energy-dispersive X-ray analysis (EDS). The imaging and analysis tools prove very effective in determining mineralogical characteristics of the aggregate and binder materials, the binder-to-aggregate ratio, the pore structure, possible secondary cements, and the presence of hydraulic and/or pozzolanic constituents. This research highlights the many benefits gained from application of traditional geological analysis techniques to the field of conservation science. In addition, the research points towards areas of future research for integrating these techniques into a standardized analysis methodology for the characterization of historic lime mortars.

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THE CRANIAL ANATOMY OF THE THEROPOD DINOSAUR SHUVUUIA DESERTI (COELUROSAURIA: ALVAREZSAURIDAE), AND ITS BEARING UPON COELUROSAURIAN PHYLOGENY

by

David Laurence Dufeau, M.S. Geo. Sci.

The University of Texas at Austin, 2003

Supervisor: Timothy Rowe

275 pages, 122 references, CD-Rom in pocket

Alvarezsaurids are a very unusual group of theropod dinosaurs whose bizarre anatomical novelties defy easy interpretation in the context of their relationship to other groups of theropod dinosaurs. The problem of resolving their affinites to any particular group or clade of theropods is compounded by the lack of any descriptions of cranial material for alvarezsaurids. Heretofore only two hypothesis for the placement of alvarezsaurids within a theropod phylogeny were published. Both analyses were conducted without the benefit of cranial material. In this thesis I describe the skulls of two specimens of the alvarezsaurid Shuvuuia deserti, and apply the data derived from that description to tests of the two competing hypotheses. The result of one of these tests is an entirely new and unexpected placement for alvarezsaurids on the theropod family tree.

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LATEST QUATERNARY STRATIGRAPHY AND SEAFLOOR MORPHOLOGY OF THE NEW JERSEY CONTINENTAL SHELF

Catherine Lorraine Schuur Duncan, PhD

The University of Texas at Austin, 2001

Supervisors: William E. Galloway and John A. Goff

A transect of multi-frequency, high resolution acoustic images calibrated by surficial samples across the New Jersey shelf (20 to 150 m water depths) resolves the shallow stratigraphic record of the Wisconsinan cycle of glaciation and global eustatic sea level change. Simrad (95 kHz) swath bathymetry and sidescan images, overlapping chirp sonar (1-15 kHz), 2D/3D Huntec (1-3.5 kHz) single channel seismic and 3.5 kHz echosounder surveys, and sediment samples comprise the transect data. The following observed stratigraphic features have been interpreted in light of the well-constrained pattern of shoreline migration, ca. 120 ka to Present: (1) During early and mid-Wisconsinan regression, a gravel-rich outwash plain covered the exposed shelf, and a marine unconformity, "R", formed on the sediment-starved middle and outer shelf. (2) About 35 ka, a muddy, marine outer shelf wedge was deposited above "R". (3) During the last glacial maximum (LGM), ca. 22 ka, the fluvial style on the exposed shelf changed from a high-energy outwash plain to a lower-energy system of N-S oriented, dendritic channels. (4) Two observed suites of iceberg keel marks suggest that icebergs grounded on the outer shelf during, or soon after, the LGM. (5) A transgressive ravinement surface above "Channels", which I have named "T", marks the migration of the shore-zone across the shelf during the latest Pleistocene and Holocene transgression, ca. 22 ka to Present. (6) The mid-shelf wedge, a prograded sediment lobe above "T", was deposited in shallow water ca. 11.5 to 8 ka, perhaps as a result of the collapse of glacial Lake Hackensack in northern New Jersey. The mid-shelf scarp, previously interpreted as a Holocene paleo-shore, is the depositional edge of the mid-shelf wedge. (7) Shelf currents have reworked the modern New Jersey seascape into a complex array of superimposed relict and active bedforms. Features older than the LGM have no seafloor expression on this shelf; there is poor correlation between shallowly buried stratigraphy and modern bathymetry.

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XENOLITH MINERALOGY AND GEOLOGY OF THE PRAIRIE CREEK LAMPROITE PROVINCE, ARKANSAS

Dennis Patrick Dunn, Ph.D.

The University of Texas at Austin, 2002

Supervisor: Douglas Smith

Three new Arkansas lamproites were delineated and evaluated during the 1980's. The intrusions were emplaced during the Middle Cretaceous Period based on stratigraphic relationships and published isotopic ages. Geological relationships record a dominant crater facies lamproite with minimal vent erosion. A 260 tonne sample taken from the two larger lamproite vents recovered 5 macro diamonds (>0.5mm) yielding a sub-economic diamond grade of ~0.04 carats per 100 tonnes. A diamond evaluation program undertaken at the Prairie Creek vent by the Arkansas State Parks Commission in the 1990's resulted in mapping of four major rock types: epiclastic rocks, olivine lamproite, phlogopite-rich tuff and olivine-rich tuff. Significant diamond contents were found only within the phlogopite-rich tuff (~0.11 carat/100 t) and olivine-rich tuff (~1.1 carat/100 t). Stratigraphic relationships indicate that the diamondiferous tuffs have undergone <50 meters of erosion. Extrapolation of the surface rock units and their diamond contents to the pre-erosion surface suggests that ~93,000 carats of diamonds were liberated and then concentrated as a natural surface enrichment.

Mantle xenoliths recovered from the Black Lick and Twin Knobs lamproite vents were analyzed for major element compositions. Their data were used to calculate a pressure-temperature array that record maximum pressures of ~5 GPa and maximum temperatures of ~1000°C for the xenolith source region. Comparisons between calculated pressures and olivine compositions indicate relatively shallow fertile mantle overlying more depleted mantle lithosphere. The two layers of mantle lithosphere may represent different ages based on their olivine composition. Crustal xenoliths include near-surface sedimentary rocks and abundant amphibolite with granitoids and rare meta-sedimentary and meta-volcanic rocks. K-Ar dates of 1.48-1.31 Ga were obtained from four amphibolite xenoliths. The cooling ages confirm that continental crust of ~1.42 Ga in age extends beneath southwestern Arkansas and that thermal effects of the younger Grenville and Ouachita orogenies were insufficient to reset the amphibole K-Ar systems. Xenolith data and published results are used to test two models for development of the Ouachita system. The first model proposes that the Ouachita trough is part of a mid-continent failed rift; the second model suggests the Ouachita System was formed at the rifted oceanic margin of the continental craton. The xenolith data support the intra-craton rift model over the oceanic-margin model.

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AN INTEGRATED EVALUATION OF A MATURE LOWER MIOCENE SILICICLASTIC GAS FIELD INCORPORATING 3-D SEISMIC, NORTHWESTERN GULF OF MEXICO SHELF

Christopher Lane Edwards, B.S.

The University of Texas at Austin, 2003

Supervisor: William Fisher

A mature gas field located in the northwestern Gulf of Mexico Basin's lower Miocene outer shelf, offshore of southern Texas, has produced from three main pay zones since 1984. The reservoirs consist of Siphonina davisi age, upward-coarsening and -thickening, moderately well-sorted, fine- to medium-grained distal deltaic sandstone packages. Hydrocarbon trapping occurs between 10800 and 12600 feet, within a growth fault's resultant rollover anticline. Porosity is relatively high, but a range of permeabilities exist due to pore-filling cementation, quartz overgrowths, pyrite and chlorite grain linings, pore-filling clay, and interbedded shales.

Based on an interpretation incorporating 3-D seismic data, the field has produced only 71.5 billion cubic feet of its 114 billion cubic feet of total recoverable gas during its 23-year history. Volumetric calculations based on the new seismic mapping suggest that two of the three main pay zones retain at least 2/3 of their original gas in place, and that another unproduced zone contains 21 BCF of untapped recoverable gas. In spite of such large calculated remaining reserves, production from 16 of the field's 18 perforations had fallen below economic rates (many without increased water production or a pressure decrease to the point of abandonment), and were consequently shut in.

The explanation for such poor recovery is threefold: (a) the character of the reservoir rock (consisting of low resistivity pay) was not well understood, resulting in (b) the abandonment of perforations as production declined, (c) without the application of modern technologies. With a better understanding of field dimensions and the application of newer technologies (such as gravel packing, fracturing, and pressure stimulation), cumulative production from this mature field could effectively triple. The evaluation of mature fields, such as is done here, is especially applicable in a time when the US petroleum industry demands more reserve growth from a considerably smaller workforce.

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GEOTECHNICAL AND ECONOMIC CONSTRAINTS OF THE US STRATEGIC PETROLEUM

Benjamin A Eisterhold M.A.

The University of Texas at Austin, 2008

Supervisor: Michael E Webber

84 pages, 29 references

The Strategic Petroleum Reserve (SPR) is a stockpile of oil that is set aside by the United States government to protect the US economy from oil supply disruptions. The oil is held in salt caverns. The 4 different sites that are currently in use are Bryan Mound, Big Hill, West Hackberry, and Choctaw Bayou. A new site is currently under construction in Richton, MS. The purpose of this manuscript is to provide an introduction on how and why the SPR was created, discuss the history of the SPR and how it works, and to make sound policy recommendations with respect to certain geotechnical and economic limitations that should influence the decisions on when to empty and fill the SPR.

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QUATERNARY SEISMIC STRATIGRAPHIC INVESTIGATIONS, YAKUTAT BAY REGION, GULF OF ALASKA: SUBGLACIAL DRAINAGE MECHANICS AND GLACIAL EXPANSE

Christopher Ryan Elmore, M.S. Geol. Sci.

The University of Texas at Austin, 2008

Supervisor: Sean P.S. Gulick

Quaternary tectonic and climate interactions have and continue to contribute to a substantial stratigraphic record that preserves the key regional events that result from the interplay of these dynamic processes. Near Yakutat Bay, Alaska, temperate glacial cover continuously manipulates and shapes the southern Alaskan margin and delivers substantial amounts of sediment annually. During cooler climatic periods, these glaciers, like most glaciers in Alaska, experience increases in volume and advance across the shelf. Using an integrated seismic data set, we investigate stratigraphic signatures buried along the shelf, between the present Yakutat and Alsek Sea Valleys, in order to understand the mechanics governing the regional glacial system during advance phases.

Our investigations reveal four glacial unconformities, of which, two show preserved retreat sediment packages. The events are indicative of ice advance phases during the Little Ice Age (LIA), the Last Glacial Maxima (LGM), and two pre-LGM events. The events show dominance by ice expanse from the Malaspina and Alsek River districts. The LGM event transgresses the shelf and concentrates erosion in highly overdeepened troughs, somewhat analogous to ice stream behavior. In addition, associated with these regional events, we find a suite of large-scale channel forms, exhibiting widths between 0.6-4.2 km and depths between 49-353 m. The channels are highly eroded vertically relative to lateral extent; widths to thickness ratios of the buried channel deposits are 15.7 on average. The channels show good correlation with the interpreted erosional events and other stratigraphic signatures indicative of ice occupation, i.e. moraines, grounding lines, etc. The channels exhibit distinct facies and facies assemblages of variable thicknesses and occurrence and show common morphologic characteristics with one another, i.e. cross-cuts. The facies and assemblages appear dominated by glacio-proximal, glacio-fluvial and glacio-lacustrine/marine physical processes. The characteristic morphology of the channels implies they are subglacially derived, and facies suggest subsequent fill by subaerial/submarine processes after ice retreat. Based on morphologic interpretations of the channels and their associations with glacial stratigraphy and erosional events, we interpret them as tunnel valleys. Expanding on their predictable relationship with specific glacial stratigraphy, we conclude that the tunnel valleys are indicators of retreat following glacial advance periods, when significant amounts of ice and melt are available to initiate and generate large tunnel valley deposits. As such, we conclude that the tunnel valleys are useful paleoclimate indicators.

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INTEGRATED SEQUENCE STRATIGRAPHY, DEPOSITIONAL ENVIRONMENTS, DIAGENESIS, AND RESERVOIR CHARACTERIZATION OF THE COTTON VALLEY SANDSTONES (JURASSIC), EAST TEXAS BASIN, USA

Tarek Abu Serie Elshayeb, Ph.D.

The University of Texas at Austin, 2004

Supervisor: Earle F. McBride

The cumulative production of the Cotton Valley Sandstones in East Texas Basin as of 1993 was 2,666 BCFG with estimated reserves of 24.2TCFG. The Upper Jurassic-Lower Cretaceous Cotton Valley Sandstone is a thick siliciclastic unit in East Texas Basin. It is characterized by low porosity (<6%) and low permeability (<0.5 md) and requires hydraulic fracturing to yield its gas. This study concerns the sequence stratigraphy, depositional environments and diagenesis of the Cotton Valley Sandstones in order to gain an insight into the processes that influenced their reservoir quality. The research involved the use of 4000 feet of conventional core, 350 well logs, and petrographic and geochemical data on sandstones, shales and organic matter. Various analytical techniques were used, including optical petrography, SEM/EDS, CL, EMP, XRD, stable and radiogenic isotope geochemistry and fluid inclusions. Six major third-order depositional sequences were identified by correlating SP and resistivity logs on 60 wells. Each sequence has identifiable highstand, transgressive, and/or lowstand system tracts. Sandstones and shales of the transgressive system tract were deposited in strike-oriented barrier island complexes and associated shelf and slope environments. Deposits of the highstand system tracts were most probably deposited in wave-dominated deltaic settings. No cores are available in the lowstand system tracts. Twenty five facies (F1-F25) have been grouped into four main facies associations that represent fully marine (FA1), marginal marine (FA2 and FA3) and back-barrier coastal plain (FA4) environments of deposition.

Cotton Valley sandstones are very fine-to fine-grained, moderately-to well-sorted quartzarenite and subarkose. The Ouachita Mountains and Arbuckle Mountains located north and northwest of the study area are most probably the main sources of sediments for the Cotton Valley clastics. Sandstones experienced extensive diagenesis that altered the original detrital composition of the sandstone and modified initial porosity and permeability.

The paragenetic sequence of the Cotton Valley sandstones include: 1) clay coatings around the detrital grains (chlorite and illite); 2) early pore-filling pyrite; 3) calcite 1 precipitation; 4) quartz cement; 5) dissolution of feldspars; 6) potash-feldspar overgrowths; 7) kaolinite and chlorite cement; 8) oil emplacement; 9) illite; 10) calcite 2; 11) dolomite and anhydrite; and 12) late diagenetic pyrite.

There are two principal internal sources of silica in the Cotton Valley Sandstones, intergranular pressure solution and dissolution along stylolites. The average quartz cement in the Cotton Valley is 11% and the calculated amount of silica derived internally from both pressure solution and stylolites constitute up to 48% of the total quartz cement. The remaining 52% come from sources that could not be quantified. Other significant local sources of silica include dissolution of quartz grains at clay laminae and at contacts between sandstone and interbedded shales, and dissolution of micron-scale detrital quartz within interbedded shales and clay laminae. High content of clay laminae are observed in cores and shale interbeds constitute up to 35% of the total CV rock volume. These sources could not be quantified. A possible external source, a silica-rich fluid expelled from the Bossier shales.

Authigenic carbonates occur as pore-filling cement and replacive phase. Calcite cement is the dominant carbonate type in the Cotton Valley Sandstones. The source of Ca for authigenic calcite is the local dissolution and reprecipitation of the carbonate shell fragments in the sandstones and the oyster-rich lagoonal limestone beds interbedded with the sandstone. The limestone beds, which range in thickness from 35 ft (10.5 m) to 50 ft (15.5 m), served as a good sealing rock as well as a potential source for calcite cement. The Cotton Valley has an average of 20%-35% shales interbedded with the sandstones; these shales could have been a significant source for iron as well as carbonates and quartz cements to the sandstones.

Original porosity loss by compaction was much more than that lost by cementation in the bioturbated Ophiomorpha-dominated sandstones and crypto-bioturbated sandstones, whereas porosity loss by cementation was more significant in the

cleaner sandstones of the laminated, tidally influenced shoreface and sand flat.

The reservoir quality of the studied sandstones is controlled mainly by depositional environment and subsequent diagenesis. Depositional environment controlled the distribution of clay matrix and oyster fragments. Clay coatings in the Cotton Valley Sandstones had a direct influence on the precipitation of quartz cement. Clay coatings retarded quartz cementation and resulted in a better reservoir quality. It was also observed that shell fragments were the primary source of carbonate cements. So, depositional environment indirectly controlled the distribution of quartz cement and carbonates in various facies.

Three main parameters influenced reservoir quality: (1) the amount of clay matrix introduced by bioturbation, (2) the amount of quartz cement, and (3) the percentage of clay coating. Cotton Valley Sandstones are divided into three main reservoir types: (1) poor reservoir quality: quartz-cemented sandstones, (2) poor reservoir quality: bioturbated sandstones with more than 15% clay matrix; and (3) good reservoir quality: clean bioturbated sandstones with less than 10% clay matrix.

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GEOMICROBIOLOGY OF SULFURIC ACID SPELEOGENESIS: MICROBIAL DIVERSITY, NUTRIENT CYCLING, AND CONTROLS ON CAVE FORMATION

Annette Summers Engel, Ph.D.

The University of Texas at Austin, 2004

Supervisor: Philip C. Bennett

375 pages, 324 references

Much of the terrestrial subsurface is inaccessible for study, but caves represent distinctive shallow subsurface habitats where biogeochemical processes can be easily examined. Previously defined speleogenesis models are almost entirely based on abiotic chemical and hydrologic controls, as biological controls on cave formation have not been considered significant. Hydrogen sulfide-rich groundwater discharges from springs into Lower Kane Cave, Wyoming, and the sulfuric acid speleogenesis model was introduced in the early 1970s as a cave enlargement process resulting primarily from hydrogen sulfide autoxidation to sulfuric acid and replacement of carbonate by gypsum on subaerially exposed surfaces. The reduced sulfur compounds serve as rich energy sources for microorganisms that colonize the cave in both subaqueous and subaerial environments. Several evolutionary lineages of the class “Epsilonproteobacteria” dominate the microbial diversity of subaqueous mats, and these microbes support the cave ecosystem through sulfur cycling and chemolithoautotrophic carbon fixation. The “Epsilonproteobacteria” occupy microbial mats in additional sulfidic cave and spring habitats, expanding the evolutionary and ecological diversity of these previously unknown organisms. The interior of the Lower Kane Cave microbial mats is devoid of oxygen and this provides habitat for anaerobic metabolic guilds, dominated by sulfate-reducing and fermenting bacteria. These anaerobic groups are responsible for autochthonous hydrogen sulfide and volatile organosulfur gas production. Cycling of carbon and sulfur compounds by the subaqueous microbial communities affects sulfuric acid speleogenesis. Compared to the total flux of sulfide into the cave, little hydrogen sulfide volatilizes into the cave atmosphere or oxidizes abiotically. Instead, the primary loss mechanism is from subaqueous microbial sulfur oxidation. Consequently, despite the cave waters being slightly supersaturated with respect to calcite, the “Epsilonproteobacteria” generate sulfuric acid as a byproduct of their metabolism, locally depress pH, and focus carbonate dissolution. The hydrogen sulfide that volatilizes into the cave air is oxidized at the cave walls where interactions between cave-wall biological and physicochemical factors influence subaerial speleogenesis and low temperature authigenic quartz precipitation. The recognition of the geomicrobiological contributions to subaqueous and subaerial carbonate dissolution fundamentally changes the model for sulfuric acid speleogenesis and the mechanisms for subsurface porosity development.

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REGIONAL TECTONICS, SEQUENCE STRATIGRAPHY AND RESERVOIR PROPERTIES OF EOCENE CLASTIC SEDIMENTATION, MARACAIBO BASIN, VENEZUELA

Alejandro Escalona, Ph.D.

The University of Texas at Austin, 2003

Supervisors: William L. Fisher and Paul Mann

222 pages, 137 references, 1 CD-Rom, 41 plates

The Maracaibo basin of Venezuela is one of the most prolific hydrocarbon basins in the world. During the Paleogene, oblique collision between the Caribbean and South American plates produced a 4-km-thick wedge of clastic sediments, where over 40 billion barrels of hydrocarbons have been produced.

Previous studies in the Eocene interval are focused either at a large regional scale or a field-size reservoir scale. Integration between both scales of observation has not been previously done, and, as a consequence, the effect of regional tectonics is not considered in the small-scale stratigraphic record. The aim of this dissertation is to study the interplay of tectonic and stratigraphic variables that controlled the Eocene sedimentation in the Maracaibo basin, and to establish a geologic model that incorporates data from a regional to reservoir scale.

Interpretation of 2-D and 3-D seismic data in the central and eastern Maracaibo basin reveals two major tectonic features formed during Paleogene collision between the Caribbean and the South American plates: 1) a late Paleocene-early Eocene foreland basin; and 2) a middle-late Eocene lateral ramp fault. The lateral ramp fault forms a paleogeographic facies boundary separating a less faulted and folded shelf area to the west from a fold-thrust belt to the east. In the Eocene Maracaibo shelf area, intraplate deformation occurs by NNE- striking left-lateral faulting with pull-apart basins localized at fault stepovers. Three-dimensional seismic time slice interpretation of more than 2000 km² of 3-D seismic data allows mapping of the Icotea pull-apart basin. Extension of the Icotea pull-apart basin is localized on pre-existing NW-SE-striking normal faults, formed by Paleocene-Eocene plate flexure during the foreland basin period.

Detailed sequence stratigraphic interpretation of the central Maracaibo basin was carried out using 330 wells and 3-D visualization methods that combined well and 3-D seismic data techniques providing greater vertical and lateral resolution (pseudo-seismic). These data reveal that Eocene clastic sedimentation is controlled by tectonic subsidence and to a lesser degree by changes in sediment supply and eustasy. Hydrocarbon reservoirs of the central Maracaibo basin are concentrated in distributary channels and tidal sand bar facies on structural highs produced by strike-slip motion of N-NE-striking faults. Depositional environments and fluid content of Eocene reservoirs are inferred from cross sections based on closely spaced well logs.

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USING CHEMICAL DATA TO DEFINE FLOW SYSTEMS IN CUATRO CIENEGAS, COAHUILA, MEXICO

Shanna B. Evans, M.S. Geo. Sci.

The University of Texas at Austin, 2005

Supervisor: John M. Sharp

The Cuatro Cienegas basin in Coahuila, Mexico was declared a National Protected Area in 1994 by the Mexican government. Its principle uniqueness is in its aquatic fauna, which are dependent on the abundant springs in this desert valley. However, the basin's hydrogeology is not very well understood. The springs in the basin have extreme variability in temperature, salinity, water chemistry, and discharge over small spatial scales. By gathering physical and chemical data in the field and using standard computer methods, the extremely complex flow systems in this critically sensitive desert wetland have been delineated. Five distinct flow systems are defined in the basin by the chemical data. These include the Churince system in the southwest, the Garabatal-Becerra-Rio Mesquites system flowing from the southwest to northeast portion of the basin, the Tio Candido-Hundidos system in the center of the eastern side of the basin, the Santa Tecla system in the southeast, and the Anteojo system in the north. The physical characteristics of the basin, including spring and canal locations, have been examined and show variable mixing within each system and complex physical flow systems. The Churince, Rio Mesquites, and Tio Candidio systems have separate source springs and terminal playa lakes. The Tio Candido and Rio Mesquites systems are related through canal and possible karst flow.

Chemical processes involved in the evolution of Cuatro Cienegas waters have been evaluated f rom the analyses of 35 samples collected in April 2004, June 2004, and January 2005. Calcium and sulfate dominate the water chemistry. However, high alkalinities are encountered in pools located closest to the mountains, especially in the Anteojo system. The Anteojo and Santa Tecla systems have lower conductivity/TDS than other systems. The water chemistry for the basin has been integrated into a Geographic Information System (GIS) to examine the spatial variations in chemistry and temperature throughout the basin. Highly saline waters (31.4 mg/L Na to 810.7 mg/L Na) are encountered throughout the basin, but the highest salinities occur toward the end of the flow systems. Furthermore, the temperature of the water at various pozas in the basin may reflect the source of the water via regional and/or karst flow. The Cuatro Cienegas water chemistry is mainly evaporation controlled, but there are other important processes involved, including the dissolution and precipitation of various mineral phases. In order to understand the variability within each flow system, a reaction pathway and mixing geochemical model has been developed for each system using PHREEQC. These baseline data provide a framework for necessary future hydrologic studies in the basin.

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PATTERN VARIABILITY IN NATURAL DUNE FIELDS

Ryan Cotter Ewing, M.S. Geo.Sci.

The University Of Texas-Austin, May 2004

Supervisor: Gary Kocurek

113 pages, 42 references

A comprehensive analysis of sand dune spacing, crest length, defect density and orientation is done in four dune fields in North America and Africa as part of a larger project investigating complexity and paleodynamics of natural dune fields. Measurements taken from Digital Orthophoto Quarter Quadrangles and Landsat ETM+ imagery of White Sands, Algodones, Agneitir, and Namib dune fields have been used in a cumulative distribution analysis. This statistical method allows for identification of different populations within the data and provides a means for comparing spacing, crest length and defect density within and between these dune fields. This method shows that in simple dune fields a single log-normally distributed population of dune spacing, crest length, and defect density occurs. In all dune fields that display compound and complex morphologies multiple log-normally distributed populations of dune spacing, crest length and defect densities occur. The trends observed in the statistical analysis show a decrease in variability as the dunes increase in spacing and crest length, and decrease in defect density. The trends of the dune crests also become more constrained to a narrower orientation as the spacing and crest length increase and defect density decreases. The trends, when used in conjunction with predictions from current models of dune formation and dating of sand dunes show a better organized pattern in the older and larger dunes supporting self-organizing computational models of dune formation. Multiple populations of dune spacing and defect density found in this study are interpreted to indicate the presence of different generations of sand dunes, created under discrete climatic events.

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QUANTITATIVE SEISMIC GEOMORPHOLOGY OF GABUS AND BELANAK FIELDS, WEST NATUNA BASIN, INDONESIA

Mochammad Fachmi, M.S. Geo Sci

The University of Texas at Austin, 2003

Co-Supervisors: William L. Fisher and Lesli J. Wood

74 pages, 25 references

Fluvial and deltaic processes, architecture, and quantitative relationships between form, fill, and process are well understood from over a century of study in modern fluvial geomorphic systems. These historical understandings, based on modern systems study, are applied to analyze the morphology of similar, ancient depositional systems as imaged in three-dimensional seismic data FROM THE West Natuna Basin, Indonesia.

The principal objectives of this research are to 1) analyze the major architectural elements such as channel width (W), meander wavelength (Lm), radius of curvature (Rc), meander belt with (B), and sinuosity (Si), that comprise the Miocene- through Holocene-age fill in the West Natuna Basin, 2) examine the morphology and character of the fluvial architectures that form the primary reservoir units in the basin and collect morphometric data on those elements, and 3) analyze those data for their interrelationships, relate the architecture of the systems to well spacing and drainage radius, and develop models for predicting reservoir character and performance in the basin.

Proportional slicing reveals that the Miocene-Holocene sequence comprises fluvial systems, shore zone systems, and shelf systems. The fluvial systems include straight river, low-sinuosity river, high-sinuosity river, anastomosing river, and braided river. There is no consistency of the channel axis, the axis repeatedly changes from an east-west orientation into a north-south orientation within the interval. The shore zone system is represented by the appearance of prograding strandplain systems. The shelf systems were identified from a very flat and uniform amplitude map.

From the morphometric measurements of 69 channels, channel width (W) ranges from 45 to 2,174 m, meander belt width (B) ranges from 243 to 8,750 m, meander wavelength (Lm) ranges from 540 to 18,450 m, radius of curvature (Rc) ranges from 119 to 4,635 m and sinuosity (Si) ranges from 1.0 to 3.4.

Several predictive relationships can be concluded from examination of the morphometrics of the WNB fluvial systems that can aid in resolving uncertainty in subsurface reservoir character [original ending-ed.]


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GEOPHYSICAL INVESTIGATIONS OF SUBGLACIAL LAKES VOSTOK AND CONCORDIA, EAST ANTARCTICA

Irina Filina, Ph.D

The University of Texas at Austin , 2007

Supervisor: Donald D. Blankenship

The subjects for this study are two subglacial lakes – Vostok and Concordia – located in East Antarctica . Lake Vostok is the largest known subglacial lake on Earth. Melting and freezing at the ice-water contact are known to occur in both lakes. These internal processes are important subjects for numerical modeling. The precise knowledge of the lake‘s bathymetry and the distribution of unconsolidated sediments at the bottom of the lake are required boundary conditions for such modeling. The ultimate goal of this research was to develop 3D bathymetry models and to establish the distribution of unconsolidated sediments for both lakes.

Joint interpretation of airborne gravity and seismic data was performed for Lake Vostok , revealing that the lake is hosted by consolidated sedimentary rocks. The modeling shows that Lake Vostok consists of two sub-basins: a larger, deeper one with water thickness exceeding 1000 m in the south and a shallower one with a water thickness of about 250 m in the north. The resulting 3D model has a substantially better correlation with seismic data than two previous models.

Lake Concordia appears to be significantly shallower with water thicknesses not exceeding 200 m for all possible host rock densities. Since the lake is relatively shallow, the sediment layer cannot be resolved. A similar pattern of freezing and melting was observed in Lake Concordia and Lake Vostok : the deeper part of the lake lies under thinner ice and is dominated by the freezing of water at the ice bottom, while in the shallower part of the lake the overlying thicker ice melts.

The analysis of seismic data in four different locations over Lake Vostok revealed the presence of unconsolidated sediments at the bottom of the lake. The sedimentary layer appears to be thicker (up to 400 m) in the northern basin, while its thickness does not exceed 300 m in the southern one.

Four different sedimentation mechanisms were considered to explain how such a thick sedimentary layer was deposited in Lake Vostok under glacial conditions. The estimates show that none of the mechanisms considered is capable of depositing the observed sedimentary layer, revealing the pre-glacial origin of Lake Vostok .


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FLUVIAL-DELTAIC AND SHALLOW-MARINE SEISMIC GEOMORPHOLOGY OF THE WEST NATUNA BASIN: IMPLICATIONS FOR RESERVOIR ARCHITECTURE AND BASIN EVOLUTION

Jed McKay Flint, MSGeoSci

The University of Texas at Austin, 2006

Supervisor: Lesli J. Wood

Quantitative seismic geomorphology and morphometric analysis of modern and paleo-landforms are powerful tools for extracting data about geologic history, processes, and fill architecture of terrestrial and marine basins. This study of the hydrocarbon-rich West Natuna Basin of Indonesia combines 3,154 km 2 of high-quality 3D seismic and analysis of 15 well logs to explain how 3D reservoir shape, size, and distribution evolve and are preserved within fluvial-deltaic and shallow-marine environments. The study also addresses how these characteristics vary in response to changes in tectonic regime and base level.

We made statistically robust, morphometric measurements of channel form and character using PC software, and where well logs have penetrated channels, we determined lithology and calculated sand percentages. The area has a variety of channel morphologies, ranging in sinuosity from 1 to 4.67 and varying in width from 30m to 4458m. Geometries range from single thread to wide, multithread. Crevasse splays and interdistributary creeks and lakes lie adjacent to channels. Sand percentages vary greatly between element types, and many multikilometer-scale elements show complex accretionary architectural composition.

The result of combining morphometric measurements with lithologic characterization is a predictive model that strengthens the relationship between channel form and sediment content. Architectural and sedimentologic changes have been assessed in the context of the basin's tectonic, climatic, and sea-level history. Results of this study apply not only to development of the study area, but to explaining how reservoir shape, size, and distribution evolve and are preserved within fluvial-deltaic and shallow-marine environments.


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DEPOSITIONAL PERIODICITY AND THE HIERARCHY OF STRATIGRAPHIC FORCING IN THE TRIASSIC CARBONATES OF THE DOLOMITE ALPS, N. ITALY

Robert Murchison Forkner, PhD

The University of Texas at Austin, 2007

Supervisor: Mark Cloos

460 pages, 174 references, 2 color plates, 11 tables

The Dolomite Alps of northern Italy are a classic field locality in the development carbonate stratigraphic theory. Included in the many discoveries rooted in the geology of the Dolomites is the concept of a hierarchy of stratigraphic forcing in the Alpine Triassic. The hierarchy states that carbonate sedimentation is dominantly a record of eustasy, resulting in organized stacking patterns, and that these stacking patterns reflect the interplay between low frequency (1-10 my) eustatic cycles and their component bundled high-frequency (100 & 20 kyr) eustatic cycles.

The overall aim of this study is to further investigate the validity of the hierarchical model after recent dating of Anisian and Ladinian successions called the Milankovitchian periodicity and/or allocyclicity of the cyclic series into question. The study was completed using four sub-studies, 3 based on data collected in the field and a fourth based in cycle theory and computer modeling. First, it can be shown that allocyclic forcing exists in the Anisian Ladinian platforms of the Dolomites by comparing the stratigraphic sections measured from 2 time-equivalent, independent carbonate platforms, the Latemar and Mendola Pass. Second, computer modeling of Anisian Ladinian carbonate platform stratigraphy using Milankovitchain solar insolation as a proxy for high-frequency eustasy shows that both pure Milankovitch forcing and mixed Milankovitch/sub-Milankovitch forcing will produce synthetic carbonate platforms with stratigraphic successions comparable to those of the Anisian Ladinian platforms of the Dolomites. Third, it can be shown that the while the Norian Dolomia Principale (a regional carbonate shelf) was affected by differential subsidence, megacycles systematically increase in their number of component cycles from 2-3:1 in the eastern Dolomites (updip) to 5-6:1 in the western Dolomites (seaward). In conclusion, the concept that carbonate platform stratigraphy is a record of an interplay between eustasy, subsidence, and sedimentation is upheld, while the validity of Milankovitchian forcing acting on all Alpine carbonate cycles is questioned. Instead, cyclic carbonates with sub-Milankovitch periodicities were common in the early and mid-Triassic, while cycles with Milankovitchian periodicities were common in the late Triassic.


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THE EVOLUTION OF A LOWER CRETACEOUS CARBONATE PLATFORM WITHIN A DIVERGENT MARGIN SETTING: THE CUPIDO FORMATION, NORTHEASTERN MEXICO

Tina Rayna Foster, M.S.Geo.Sci.

The University of Texas at Austin, 2003

Supervisor: Robert K. Goldhammer

226 pages, 127 references, 8 plates

The Lower Cretaceous Cupido Platform of the western Gulf of Mexico provides an example of passive margin platform development which is disrupted by the syndepositional movement of salt in the subsurface. This study focused on the recognition, formation, probable local and global controls, and the contribution of cyclicity to the development of carbonate platform architecture during a greenhouse period in a divergent margin setting. The Cupido Formation may provide an outcrop analogue of high resolution sequence stratigraphy for its subsurface equivalent, the Sligo Formation of Texas.

A depositional model encompassing nine lithologic subfacies was created for the platform interior of the Cupido Formation from the analysis of measured sections exposed near Monterrey, Mexico. The model consists of a shallow rimmed platform with a stable grainstone shoal acting as the shelf crest in place of the actual rudist dominated shelf margin. This model is further supported by the recognition of a shoal complex within the subsurface Sligo Formation located just above mobile evaporites which formed antecedent topography for the Mesozoic carbonate platforms.

A variety of peritidal and subtidal meter-scale cycles were identified based on their position within the platform interior. One-dimensional stacking pattern analysis, including facies proportions and thickness trends of the high frequency cycles, resulted in the recognition of depositional sequences. Depositional sequences with similar trends and system tract proportions aided in the development of a lower order supersequence. The Cupido Platform was accordingly divided into a highstand with progradational basinal turbidites, fore-slope, reef, and aggradational platform interior facies and a transgressive systems tract comprised of retrogradational platform interior facies.

Two-dimensional analysis of the measured sections was accomplished using thickness variations and the presence of extensive, shallow marine evaporites. Using the second order sequence boundary as a datum two additional depositional sequences were recognized in the landward portion of the platform. The deposition of these sequences occurred simultaneously with the deposition of the La Pena Shale as it drowned the shoal complex in the later stages of the lower order transgression. These retrogradational geometries in the Cupido Platform are supported by landward thickening in the transgressive portion of the Sligo Formation.

The most pervasive controlling factor throughout the formation of the Cupido Platform is its deposition during a long term greenhouse period. The greenhouse climate resulted in the retrogradational geometries of the shelf, in the absence of high frequency sequences, and the moderation of sealevel amplitude. The eustatic frequency of cyclicity is disturbed by the presence of large scale syndepositional faults between the shoal complex and shelf margin, which resulted in the dramatic increase of accommodation space available for sedimentation. The development of these growth faults is related to the movement of basin wide evaporites, as suggested by seismic interpretations of the Sligo Formation.

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PHYSICAL MODELING OF EVAPORITE-DETACHED SALIENTS

Christine René Zúñiga Fox , M. S. Geo. Sci.

The University of Texas at Austin, 2005

Supervisors: Randall A. Marrett and Bruno C. Vendeville

The use of scaled physical modeling of thin-skinned fold-and-thrust belts allows for the isolation of key parameters in the development of convex-toward-the-foreland folds and thrusts. Unlike salients formed in natural settings, scaled physical models can be monitored through time, with structures dissected and analyzed at the completion of the experiment. Conducting strain and displacement vector analysis of individual model stages yields quantitative insight into the kinematics of salient development.

I constructed twenty-one scaled physical models in order to study the processes leading to the formation of salients and extrapolate the models to natural examples. Thus, variation of model rheologies and boundary conditions test the influence of stratigraphic parameters on the formation of salients in thin-skinned fold-and-thrust deformation belts.

The physical models created for this study reveal that the pre-collisional foreland, lateral, and hinterland evaporitic décollement boundaries exert great influence on the degree of fold and thrust curvature across the salient, the presence of vertical-axis rotation during salient formation, and the geometry of the structural trend line patterns of folds and trusts within the salient. Brittle/viscous models showed two distinct patterns of fold curvature, local curvature near the décollement pinch-out, and distributed curvature above the evaporitic décollement, dependent on the lateral and hinterland boundaries of the décollement. Fold axial traces initiated with localized curvature above the lateral pinch-out, while structures maintained linear axial traces above the central décollement layer in models with lateral boundaries perpendicular to convergence direction of a linear indenter. However, I found that vertical-axis rotation of the folds and thrusts did occur. Conversely, fold axial traces initiated with distributed along strike curvature in models with a pre-collisional hinterland protruding décollement. Fold axial traces in viscous/viscous models initiated with localized or distributed along strike curvature that became more convex with progressive deformation. Vertical-axis rotation also occurred in these models.

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EVOLUTION OF THE BRAIN IN THEROPODA (DINOSAURIA)

Jonathan William Franzosa, Ph.D.

The University of Texas at Austin, 2004

Supervisor: Timothy B. Rowe

357 pages, 155 references, 1 CD-ROM

The description of natural and artificial endocasts has become routine since the work of Tilly Edinger. Most workers write little more than simple descriptions of isolated specimens because endocasts are rare, and scattered throughout the world. Harry Jerison took the next step and broadly compared endocasts in detail, using them for evolutionary studies of brain size and intelligence. In those studies, Jerison concluded that dinosaurs (excluding birds) had the brain size expected for "reptiles" of their size. However insightful, many equations and assumptions Jerison used are now questioned. The goals of this study are to continue the comparative work of Edinger and Jerison, and to employ more modern techniques and information than was available when Jerison's studies were conducted, to either verify or overturn his hypotheses.

Most of this study was completed using the Department's High Resolution X-ray Computed Tomographic (CT) Scanner, which allowed digital endocasts to be made from intact braincases. This increased the number of taxa available for analyses to 18. These endocasts are described in detail, allowing 14 characters to be identified and scored. Several analyses are done, one using just the examined taxa and characters, and three in which the characters are added to existing data matrices. These analyses showed the 14 characters contain useful phylogenetic information, and one of the phylogenies had a polytomy resolved owing to the addition of the characters.

The endocast characters also show similarities in brain architecture between pterosaurs and birds, and indicate that an avian-style brain evolved gradually through the theropod lineage. The character transitions that show the gradual evolution in the cerebral hemispheres, optic lobes, floccular lobes, and other brain features in the sequence of studied endocasts form the basis for testing inferences about theropod biology, behavior, and intelligence. Trends concerning theropod sensory and prey catching ability are tested and supported, indicating that theropods became more dependent on sight, and less dependent on smell, over time, and developed better hand-eye coordination, agility, and balance for capturing smaller prey, whereas using Encephalization Quotients for intelligence determination is disputed. This hypothesis testing is one of the strengths of digital endocasts.

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FACIES HETEROGENEITY, PLATFORM ARCHITECTURE AND FRACTURE PATTERNS OF THE DEVONIAN REEF COMPLEXES, CANNING BASIN, WESTERN AUSTRALIA

Edmund Locke Frost III, Ph.D.

The University of Texas at Austin, 2007

Supervisor: Dr. Charles Kerans

Carbonate facies patterns and stratal architecture are the product of the complex interaction of internal (e.g., reef-building biota, sediment production) and external drivers ( e.g., tectonics, climate, and relative sea level). In the Canning Basin of Western Australia, many of these drivers are in flux across the Late Devonian Frasnian–Famennian (F–F) boundary and significant variations in reef-building biota and long-term accommodation are observed. This study documents the evolution of the Canning Basin's Devonian reef complexes across the F–F boundary and proposes a new interpretation of the stratal architecture and paleobathymetric profile of the Famennian. Data presented here demonstrate the evolution of a shelf-crest system in the Famennian, with beds expanding basinward and the reef growing in water depths of approximately 5-15 m. The paleobathymetric profile of the Famennian described by this study represents a departure from the well-documented barrier-reef system of the Frasnian. Digital outcrop models help capture the heterogeneity of the Famennian system and allow for characterization of the Devonian reef complexes across the F–F boundary.

Syndepositional fractures are a ubiquitous feature of high-relief, reef-rimmed carbonate systems and these features exert a profound influence on many facets of platform evolution. This study documents strong variability in syndepositional fracture patterns as a function of lithofacies and depositional setting and evidence for the temporal evolution of the mechanical properties of the Devonian reef complexes is presented. A statistically significant relationship is documented between syndepositional fracture development and variations in stratigraphic architecture, approximated here by platform-margin trajectory. This relationship implies a significant stratigraphic control on syndepositional deformation in carbonate platforms and suggests that external drivers are not required to generate early fractures in high-relief carbonate platforms.

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GEOCHRONOLOGY OF HEIMEFRONTFJELLA, EAST ANTARCTICA WITH IMPLICATIONS FOR GRENVILLIAN AND PAN-AFRICAN OROGENESIS

Roy Westin Fuller, M.S.

The University of Texas at Austin, 2003

Supervisor: James N. Connelly

104 pages, 50 references, 2 plates

Heimefrontfjella, a mountain range in East Antarctica, records a complex, multi-phase geologic history that previous workers have suggested contains evidence of both ca. 1100 Ma (Grenvillian) and ca. 500 Ma (Pan-African) aged tectonic events. This study characterizes and further constrains these events by utilizing field and petrographic observations to produce a relative time framework. This framework is constrained by twelve new U-Pb zircon, U-Pb monazite, U-Pb titanite, and K-Ar amphibole dates.

Grenvillian igneous intrusions comprise orthogneissic rocks (I 1 ), dated at 1102+5/-3 Ma and foliated megacrystic granite to diorite (I 2 ), dated at 1099+13/-6 Ma, 1097+6/-4 Ma, and 1086+6/-4 Ma. Grenvillian metamorphism and deformation occurred in two episodes. The first phase was intense migmatization of I 1 orthogneissic rocks (D 1 /M 1 ), constrained, based on field observations, to have intruded during an interval between I 1 and I 2 intrusion. A second phase of deformation and metamorphism (D 2 /M 2 ) is dated between 1064 to 1010 Ma and occurred at granulite-grade conditions, as indicated by orthopyroxene in granitic rocks. D2/M2 is directly constrained by metamorphic zircon that crystallized at ca. 1064 Ma, and zircon and monazite overgrowths that range in age from 1010 to 1020+/-25 Ma.

Voluminous mafic dikes (I 3 ), for which absolute ages were not obtained, are inferred to postdate, based on petrography and field observations, the above-described Grenvillian tectonic features, but predate Pan-African deformation.

Deformation and metamorphism during the Pan-African period (D 3 /M 3 ) produced penetrative fabrics and discrete shear zones at amphibolite grade metamorphic conditions. A range-wide right-lateral shear zone, the Heimefront Shear Zone, developed at this time. The age of Pan-African deformation and metamorphism is directly constrained by monazite dates of 503+/-1 Ma, 501+/-1 Ma, and 500+/-2 Ma, amphibole dates of 544+/-22 Ma and 528+/-22 Ma, and a titanite date of 515+/-6 Ma.

The above framework is permissive of the theory presented by previous workers that Heimefrontfjella was contiguous with the Namaqua-Natal orogenic belt in Africa during Grenvillian TimesNewRoman, associated with Rodinia convergence. The ca. 500 Ma ages together with field and petrographic observations, confirm that Heimefrontfjella was part of a Pan-African orogenic belt associated with convergence of Gondwanaland, either as an extension of the Mozambique Belt in Africa that resulted from collision of the Indo-Antarctic plate with West Gondwana, or as a later orogenic belt associated with collision of the East Antarctic Plate with West Gondwana.

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MODELING REFLUX DOLOMITIZATION

Shawn M. Fullmer, M.S.

The University of Texas at Austin, 2005

Supervisor: F.J. Lucia

The process of reflux dolomitization is commonly invoked to explain dolostone occurrence and distribution. The time required for this process to take place is not well understood. Volumetric flow rates are the dominant control on the time requirement. Published platform scale numerical models of reflux require unrealistically high permeability values and reaction efficiencies to explain the mapped dolomite volume. Approaching the problem at the high-frequency-cycle scale allows tighter constraints on the variables and a simpler geologic setting to investigate the permeability and reaction efficiencies required to form a dolostone unit.

The high-frequency cycle used as a model in this study is located near the top of the Upper Glen Rose Formation. It is an upward shallowing, Albian age cycle that consists of a subtidal mud-dominated packstone overlain by an evaporitic tidal-flat cap. The dolostone extends 1.5 meters down from the cycle top. Permeability values reflecting conditions at the onset of dolomitization were reconstructed by, 1) obtaining current porosity and permeability values from outcrop samples, 2) approximating porosity loss due to burial diagenesis, 3) interpreting pre-dolomitization rock fabrics from thin sections, and 4) calculating permeability using the uncompacted porosity and rock-fabric information. The data was entered into a variable density flow model and the results suggest that the time required to form this 1.5 m dolostone unit is between 300 and 1,000 years using a harmonic mean permeability of 260 md (2.6 x 10 -13 m 2) and dolomite reaction efficiencies between 10-40%. These more realistic permeability and efficiency values are much lower than the 100 – 10,000 Darcy’s (10 -11 – 10 -9 m 2) permeability and 100% reaction efficiency values used in current published reflux models.

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CENOZOIC TECTONICS OF THE NICARAGUAN DEPRESSION, NICARAGUA, AND MEDIAN TROUGH, EL SALVADOR, BASED ON SEISMIC REFLECTION PROFILING AND REMOTE SENSING DATA

Justin O'Leary Funk, M.S. Geo. Sci.

The University of Texas at Austin , 2007

Supervisors: Drs. Paul Mann and Kirk McIntosh

Lakes Nicaragua and Managua are the two largest lakes in Central America and cover a combined area of ~9000 km 2 of the presently active Central America volcanic front (CAVF). As part of the Subduction Factory focus area of the U.S. National Science “Margins” program, we acquired ~1925 km of shallow geophysical data over Lakes Nicaragua and Managua in May, 2006, to establish their late Quaternary structural and stratigraphic history and to better constrain regional models for active tectonics in western Nicaragua and El Salvador. In order to investigate regional, upper crustal deformation resulting from forearc sliver transport and/or slab rollback of the Cocos plate, I took a multidisciplinary approach by integrating these new data with: relocated earthquake epicenters; earthquake focal mechanisms; high-resolution digital topography from the NASA Shuttle Radar Topography Mission (SRTM); published global positioning system (GPS) vectors showing recent plate motions; onland geologic maps showing bedrock geology; previous maps of lake bathymetry and bottom sediment types; a previously unpublished, regional aeromagnetic data set; and multichannel seismic reflection profiles from the Gulf of Fonseca and Pacific Ocean. Both lakes and the Gulf of Fonseca occupy the Nicaraguan depression, which is an elongate, asymmetrical, 40-100-km-wide depression extending 342 km across the length of Nicaragua , across the 57-km-wide Gulf of Fonseca, and 225 km into the neighboring country of El Salvador where it is called the Median trough. Profiles across the Nicaraguan depression using subbottom profiles and high-resolution SRTM topographic data indicate that the basin structure is a highly asymmetrical half-graben bounded to the southwest by northeast-dipping faults with basement shallowing to the northeast. Depth to basement in the lakes area is uncertain due to the lack of deep-penetration multichannel seismic data and exploration wells. Depth to basement in the Gulf of Fonseca is also not known but does contain an overlying asymmetrical wedge of low-velocity sediments based on multichannel seismic velocity models.

New multichannel seismic, subbottom profiler, and bottom core data from the 2006 NicLakes study have improved bathymetric, bottom sediment, and recent fault maps for both lakes that can be compared to previous, speculative models for the lake's geology and tectonics. Previous work using only subaerial observations from the Nicaraguan depression - Median trough have proposed three different models for the formation of the depression and its active, seismogenic transverse faults: 1) Neogene normal faulting parallel to the length of the depression induced by slab rollback of the underlying subducted slab of the Cocos plate beneath Nicaragua and El Salvador; the zone of extension is proposed to have migrated from the northeast to the southwest from Miocene to the present; 2) Neogene to present right-lateral strike-slip faulting parallel to the volcanic front and offset locally by pull-apart basins, or centers of fault-bounded extension 3) Negoene to present right-lateral strike-slip faulting parallel to the volcanic front that is accommodated by left-lateral transverse or “bookshelf faults” at high angle to the volcanic front. The 2006 data set combined with the many preexisting data sets listed above have been integrated into three regional structural cross sections. These sections show the asymmetrical half-graben structure for the Nicaraguan depression-Median trough. The area of greatest subsidence and footwall uplift is in the Lake Nicaragua area; in the southeast; the area of least subsidence/footwall uplift is in the Gulf of Fonseca in the northwest. I interpret this structural pattern as a time-transgressive basin opening with the oldest extension pre-Miocene) starting in the southeast and migrating to the northwest. GPS data indicates that this earlier phase of intra-arc rifting is now being modified by arc parallel shear related to the northwestward transport of the Central American forearc sliver.

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CALC-SILICATE ALTERATION AND CU-AU MINERALIZATION OF THE DEEP MLZ SKARN, ERTSBERG DISTRICT, PAPUA, INDONESIA

Laurel Michelle Gandler, M. S.

The University of Texas at Austin , 2006

Supervisor: J. Richard Kyle

The Deep Mill Level Zone Cu-Au skarn deposit is developed in an Upper Cretaceous to Lower Tertiary siliciclastic and carbonate succession adjacent to the 3-Ma Ertsberg pluton in the Central Range of New Guinea. The DMLZ is the deepest explored part of the Ertsberg East Skarn System that consists of the surface Gunung Bijih Timor (GBT) deposit at 4200 m elevation, through the Intermediate Ore Zone (IOZ), Deep Ore Zone (DOZ), Mill Level Zone (MLZ) and Deep Mill Level Zone (DMLZ) at 2900 to 2600 m. The DMLZ is hosted by mixed assemblages of siliciclastic and dolomitized carbonate strata that produce Mg-rich skarn assemblages. Alteration can be divided into types based on dominant lithology as 1) forsterite-diopside skarn, 2) anhydrite skarn, 3) massive sulfide, 4) magnetite skarn, 5) hornfels, 6) marble and 7) endoskarn within the Ertsberg Diorite.

Samples distributed over 300 m of vertical depth were examined petrographically and 23 were selected for chemical studies. Forsterite is the dominant olivine phase that ranges from Fo 89-100 Fa 0-3 Te 0 from 11 grains . Forsterite is commonly altered to serpentine and is associated with magnetite, anhydrite and phlogopite. Magnetite skarn contains olivine that is more Fe-rich. Clinopyroxene compositions range from Di 73-99 Hd 1-26 Jo 0-1 from 18 grains. Diopside is locally altered to tremolite and is associated with anhydrite, talc, and carbonate minerals. Garnet compositions range from Ad 43-99 Gr 0-54 Py 0-5 from 13 mineral grains. Garnet in hornfels shows compositional zoning due varying Fe and Al concentrations. Periclase after dolomite is present locally. Secondary Fe- and Mg-rich carbonate phases are common as disseminated crystals or rims on earlier carbonate crystals.

Cu-Au mineralization consists of bornite and chalcopyrite predominantly within magnetite and anhydrite skarn; pyrite and pyrrhotite are locally present. The dominant prograde skarn assemblages are controlled by protolith composition, notably the relative abundance of quartz, dolomite and calcite within the host Waripi Formation. Isochemical metamorphism of mixed assemblages of quartz and dolomite produce the greatest change in mineralogical composition and decrease in mineral volume, forming forsterite-diopside dominant skarn assemblages. Magnetite is commonly associated with forsterite-diopside mineralization and is associated with Cu-Au mineralization. Structural features created weakness zones that created fluid pathways responsible for the formation of the Ertsberg East mineralizing system. Magnetite skarn was introduced during the metasomatic fluid phase, and these fluids were also responsible for the emplacement of Cu and Au. Economic Cu and Au mineralization was locally controlled by host lithology.

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UPPER MANTLE SEISMIC STRUCTURE BENEATH THE CENTRAL RIO GRANDE RIFT AND BENEATH EASTERN MEXICO AND THEIR IMPLICATIONS

Wei Gao, Ph.D.

The University of Texas at Austin , 2006

Supervisor: Stephen P. Grand

I present new images of the P- and S-wave seismic structure of the upper mantle beneath the central Rio Grande rift and surroundings and beneath eastern Mexico . The upper mantle structure is determined using traveltime delays and seismic waveforms.

The P- and S-wave tomography beneath the rift is derived through the LSQR algorithm. Tomography shows large seismic anomalies (up to 5% and 8% variation in P- and S-wave respectively) in the shallow mantle. Beneath the rift and Mount Taylor lies the seismically slow shallow mantle that primarily caused by higher temperature with possibly a small amount of partial melt. The mantle deeper than 150-km beneath the rift is not anomalously slow. A fast anomaly near 500-km depth beneath the central Colorado Plateau is probably the trailing edge of the Farallon slab. A slow seismic anomaly to the east of that anomaly at 400-km depth appears to connect to the slow shallow anomaly beneath the Mount Taylor . Beneath the Great Plains a narrow fast structure is imaged throughout the upper mantle from 200 to 600-km depth. They may form small-scale convection beneath the central rift and surrounding region.

The P and S velocity models beneath eastern Mexico are derived through waveform inversion of triplicated P and S waves using a conjugate gradient algorithm. The optimal models have discontinuities of 6.2% and 7.3% at 410-km depth and 3.3% and 6.3% at 660-km depth for P and S respectively. A common feature of the models is a low velocity zone above the 410-km discontinuity, which may be due to partial melt induced by water release from the transition zone. The overall jump in velocity at 410-km is also larger than in previously published models. Another feature is that P-wave data require a small discontinuity at 490-km depth and S-wave data require an additional discontinuity at 600-km depth. This may be a thermal anomaly due to a flat lying slab or might reflect a phase change in the transition zone.

Also, I present a new technique for regional-scale joint inversion of body and surface waves and show its strengths using synthetic and real datasets.

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IMPACT OF FLUID EVOLUTION ON GARNET GROWTH IN PELITIC ROCKS FROM HARPSWELL NECK, MAINE

Joshua Garber, B.S.

The University of Texas at Austin, 2008

Supervisor: William Carlson

Complex and varying compositional zoning patterns in garnets in pelitic schists from Harpswell Neck, Maine have been attributed by various authors to equilibrium growth and coalescence of separately nucleating neighboring crystals, to overprint zoning modulated by prograde thermal effects, and to overprint zoning during nearly isothermal growth in the presence of fluids of variable composition. To help resolve this controversy, detailed field observations of the relationships among the structure and timing of multiple vein generations and garnet growth were combined with microchemical analysis of fluid inclusions in vein quartz and garnet.

Regional structures record shortening in NNE-trending tight folds and subsequent NNE shearing along kilometer-scale strike-slip faults. Three generations of quartz veins were discriminated in the field on the basis of their relationship to these structural features and cross-cutting relationships. Garnet growth is interpreted to have begun during the emplacement of the first generation of veins and to have continued during the emplacement of the second. Fluid inclusions in garnet are too rare and small for accurate analysis, but fluid inclusions in quartz veins related to garnet growth revealed two separately preserved fluids, one H2O-rich and one CO2-rich.

In the regional structural context, patterns of mineral inclusions in garnet reveal that nucleation of garnet porphyroblasts occurred during folding, with growth and some continued nucleation continuing during subsequent strike-slip shearing. Nucleation and early garnet growth is interpreted as synchronous with a dense CO2-rich population of fluid inclusions, whereas later garnet growth appears to have been related to the H2O-rich fluid trapped in later inclusions. Thus, the anomalous zoning patterns seen in Harpswell Neck garnets may be attributed to a distinct change in metamorphic fluid composition and elemental solubility. In this scenario, the early CO2-rich fluid enhances solubility for elements like Ca and Y but inhibits the diffusion of Mg, Mn, and Fe, whereas the late H2O-rich fluid is responsible for equilibrating all of these elements at the garnet rims.

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URBAN EFFECTS ON GROUNDWATER RECHARGE IN AUSTIN, TEXAS

Beatriz Garcia-Fresca, MSGeoSci

The University of Texas at Austin, 2004

Supervisor: John M. Sharp, Jr.

175 pages, 157 references, 1 plate

Cities and urban populations are growing at a high pace, but groundwater remains an underutilized resource in most urban areas. The general impacts of urban development on groundwater include overexploitation; subsidence; decreasing quality; salt-water intrusion; disruption of ecosystems; variations in the local climate; properties of the soil; natural drainage network; and the quantity, quality, and location of both recharge and discharge. The shallow urban underground is an intricate network of tunnels, conduits, utilities, and other buried structures comparable to a natural karstic system, except that "urban karst" is generated much faster. Urbanization also introduces new sources of water, resulting in an increase of groundwater recharge. These sources include irrigation of parks and lawns, leakage from water mains and sewers, and infiltration structures.

The areal extent of Austin, Texas, has grown steadily since 1885 but has increased five-fold since the 1960's. The difference between the amount of tap water treated in the City of Austin and the amount of sewage that arrives in the wastewater treatment plants (or excess urban water), represents the amount of urban water potentially available for recharge. A water balance shows that about 7% of the treated drinking water is estimated to be lost to leaks from the distribution network and 5% to leaks from sewers. The rest of the excess urban water is used in irrigation of parks and lawns, some of which will be evapotranspired and some will turn into recharge. Smaller fractions are recharged in septic tanks and other designed infiltration devices. Direct recharge from rainfall has decreased as a result of the introduction and expansion of impervious pavements, from 53 mm/a under preurban conditions to 31 mm/a in the year 2000. However urban sources of recharge contribute an average of 85 mm/a of excess urban water, resulting on an urban recharge of 63 mm/a, and a total recharge rate that could equal 94 mm/a.

Several hydrogeochemical parameters were tested as tracers of urban recharge in Austin. Chlorination by-products (trihalomethanes) were found in high concentrations in tap water and in low concentrations in wastewater. However, they were not detected in either surface water courses or groundwater. δ 15N is a commonly used indicator of leakage from sewers, but unusually low values were obtained. Finally, 87Sr/ 86Sr of dissolved strontium shows a strong trend that can be related to the degree of urbanization over the Barton Springs segment of the Edwards aquifer. Values of this ratio from the lesser urbanized wells indicate groundwaters close to equilibrium with the limestone, while samples from the more urbanized wells show higher values, which are closer to those of tap water.

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STRATIGRATIGRAPHIC ARCHITECTURE AND BASIN FILL EVOLUTION OF A PLATE MARGIN BASIN, EASTERN OFFSHORE TRINIDAD AND VENEZUELA

E milio José Garciacaro, M.S. Geo Sci.

The University of Texas at Austin , May 2006

Supervisors: Paul Mann and Lesli Wood

Eastward migration of the Caribbean plate relative to the South American plate is recorded by a 1100-km-long foreland basin which is oldest in the west (Maracaibo basin, 65-55 Ma) and youngest in the east (Columbus basin, eastern offshore Trinidad, 15-0 Ma). Regional transpression has caused lithospheric loading and flexure along the northern margin of South America creating a large foreland basin area which propagated from west to east as the Caribbean plate moved eastward relative to the South American plate. I have integrated 775 km of deep-penetration 2D seismic lines acquired by the 2004 BOLIVAR survey, 325 km of 1975 GULFREX seismic data, 8,000 km2 of industry 3-D seismic data, and published industry well data from offshore eastern Trinidad .

Interpretation of seismic sections tied to wells reveals the following fault chronology: 1) middle Miocene thrusting along the Darien ridge related to highly oblique convergence between the Caribbean plate and the passive margin of northern South America; continuing thrusting and transpression in an oblique foreland basin setting through the early Pleistocene; 2) early Pliocene-recent low-angle normal faults along the top of the Cretaceous passive margin; these faults were triggered by oversteepening related to formation of the downdip, structurally and bathymetrically deeper, and more seaward Columbus basin; large transfer faults with dominantly strike-slip displacements connect gravity-driven normal faults that cluster near the modern shelf-slope break and trend in the downslope direction; to the south no normal faults are present because the top Cretaceous horizon has not been oversteepened as it is adjacent to the foreland basin; 3) early Pliocene-Recent strike-slip faults parallel to the trend of the Darien ridge and accommodate present-day plate motions.

Active mud diapirism in the Columbus basin is widespread and is related to overthrusting and loading of upper Miocene-lower Pliocene age mud. Analysis of the 3-D seismic data reveals the presence of extensive gravity-flow depositional elements on the Columbus basin deepwater area, characterized by mass-transport deposits at the base, turbidite frontal-splay deposits, leveed-channel deposits, and capped by fine-grained condensed-section deposits. Deep basin wells drilled in recent years have proven that turbidites were transported into the Columbus basin deepwater during the Plio-Pleistocene. Analysis of these well results suggest that a deeper oil charge is present within the Columbus basin deepwater area. The primary uncertainty for this variable hydrocarbon system is whether fault or diapiric pathways connect the petroleum charge at depth with shallower reservoir rocks.

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GEOCHEMICAL EVOLUTION OF GROUND WATER IN THE BARTON SPRINGS SEGMENT OF THE EDWARDS AQUIFER

Bradley Dean Garner, M.S. Geo. Sci.

The University of Texas at Austin, 2005

Supervisor: Jay L. Banner

The water quality in a karst (limestone) aquifer changes over time, making the application of traditional hydrogeologic principles difficult or impossible. This research’s goal was to advance the understanding of the Barton Springs segment of the Edwards aquifer within and around Austin, Texas. This was accomplished by analyzing time - series water - quality data from long, medium, and short time scales. Analysis provided insights into direction of ground - water flow, sources of spring discharge, and mixing of geochemically distinct waters in the aquifer. The results of this research are of interest because of the aquifers role as a drinking water supply, its role as a habitat for the endangered Barton Springs salamander ( Eurycea sosorum ), and for its central role in creating the popular Barton Springs Pool.

Twenty - six years of water - quality data were compared against contemporaneous streamflow and spring discharge rates to evaluate ground - water connection to surface - water processes. Fifteen of 26 wells in this dataset showed a correlation between these measurements. Ion ratios of Mg/Ca, SO 4 /Cl, and Na/Ca showed that active ground - water processes included dilution by recently - recharged surface water, inconguent dissolution, and mixing with water from a saline zone and an underlying aquifer. Four wells were shown to intersect major flowpaths, and five wells were shown to intersect minor flowpaths.

Major ion and Sr isotope data collected over two years from four karst springs ( Main, Eliza, Old Mill, and Upper Barton Springs) provided insight into water flow in the aquifer. Main and Eliza were fed by ground water from the same flowpath(s) in the aquifer, as their geochemical compositions were indistinguishable. Old Mill received 4–9 percent of its water from a saline zone, as shown by elevated ion concentrations and a quantitative mixing model. Upper Spring obtained some of its water from an isolated subbasin in the aquifer, as indicated by radiogenic 87 Sr/ 86 Sr values measured in this subbasin. Oxygen and hydrogen isotope values indicated that ground water was well - mixed over year or longer timescales.

Oxygen isotope samples collected from the springs following a rainfall event showed how stormflow recharge flows to the springs. A hydrograph separation using showed an immediate increase in spring discharge following rainfall but a 12 - hour delay before storm water reached the spring. This suggested an advancing front of storm water that expelled pre - storm water from the karst conduits. Discharge of pre - storm ground water was reduced by up to 44 percent after rainfall, suggesting that stormflow pressurized the karst conduit system and reduced gradients between the aquifer matrix and conduits. Specific conductance was also an effective and inexpensive tracer of stormflow, on the basis of its strong correlation (r 2 =0.96) to oxygen isotope values. Resource managers and scientists may be interested in these findings, as the potential for contamination of this spring system is increased after large rainfall events.

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CHARACTERIZATION OF TRANSPORT PROPERTIES IN GRANITIC ROCK FRACTURES WITH SKINS

Terence Travis Garner, PhD

The University of Texas at Austin, 2007

Supervisor: John M. Sharp, Jr.

191 pages, 149 references, 11 tables

Hydraulic properties of fracture skins in granitic rocks from three climatically different field sites show that fracture skins can increase permeability, compared to unaltered granite, through microfractures or weathering rinds, or decrease it through the effects of mineral nucleation or precipitation and growth of biological organisms. In comparable granitic crystalline rocks, fracture skins formed in more arid climates have a higher porosity than fracture skins formed in more humid climates. Granite fractures have been collected from three field sites Elberton, Georgia, Fredericksburg, Texas, and Eyre Peninsula, South Australia. Fracture skins in Elberton are predominantly surface coatings of dust films, clay infillings, organic growths, and infillings of iron precipitates. Town Mountain Granite skins are dominated by iron banding, weathering rinds, and surface coatings of pyrolusite. The Caica Granites from the Eyre Peninsula have similar fracture skins to the Town Mountain Granite, but skin thicknesses are greater. Modeling studies with fracture skins demonstrate that the most important hydraulic properties are skin porosity, diffusion coefficients, and retardation. Through combined laboratory analyses and field investigations, the variations in transport properties of rock matrix and fracture alteration zones are documented. Transport properties of fracture skins in granitic rocks with surface coatings enhance fracture transport and alteration zones of more porous skins attenuate transport. A new laboratory method is employed to measure diffusion coefficients using laser ablation ICP-MS. Diffusive transport is shown to be preferential to grain boundaries and zones of mineral cleavage planes. Tracer tests show channeling to be a significant factor in breakthrough results on the field scale. Channels on the field scale are imaged using high frequency GPR providing an image of preferential flow paths in a fracture.

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3-D SEISMIC EVALUATION OF FAULT CONTROL ON QUATERNARY SUBSIDENCE PATTERNS, RATES, AND RELATED SURFACE MORPHOLOGY IN SOUTHEASTERN LOUISIANA

Terra Jane George, MS. GeoSci.

The University of Texas at Austin, 2008

Supervisor: David Mohrig

168 pages, 69 references, 11 tables

Throughout the past century, the Louisiana coastline has been deteriorating at an alarming rate. Fault induced subsidence has been suggested to be one of the likely drivers of this land loss. I directly addressed the control of faulting on Quaternary delta subsidence using subsurface architectural data.

I carried out a systematic process for evaluating fault movement on individual faults in the subsurface by using an industry grade 3-D seismic survey to evaluate the interaction of complex fault patterns and shallow substrate (< 1s or 1,000m). Using amplitude data, as well as a coherency algorithm, horizons and faults were mapped in ~1400km2 of data in southeastern Louisiana. Measurements of fault displacement were obtained by determining time offset of synchronous horizons. Down-to-the-basin and counter-regional growth faulting was observed. Both styles of faulting are associated with movement of Jurassic-age salt deposits and display measurable offset at depths as shallow as ~.450s (roughly 380m). Fault displacements increase roughly linearly with burial depth. The displacement data together with well-log data provide a tentative Quaternary rate for the normal faulting of 0.1mm• yr-1 to 1mm• yr-1.

I have assessed the possible control of subsurface faulting on surface topography using co-registered maps of fault traces and orthophoto quadrangles. This analysis has revealed a number of instances where faulting affects modern surface morphology. Often, the up-thrown sides of growth faults are capped by marshland, whereas the downthrown blocks are drowned by ~.7m of surface water (Snedden et al., 2007). Further, the influence of faulting extends to the modern planform of the lower Mississippi River, as data indicate that growth faults control the position of a major bend near the river’s outlet.

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LATE CENOZOIC SEDIMENTATION AND TECTONICS OF THE BADA, DANDERO-MAHABLE AND ABDUR AREAS, NORTHERN DANAKIL DEPRESSION, ERITREA, AFRICA

Berhane Negassi Ghebretensae, MS

The University of Texas at Austin, 2002

Supervisor: Richard T. Buffler

161 pages, 72 refs, 0 plates

Three sub-basins (Bada, Dandero-Mahable and Abdur) in the northern Danakil Depression of Eritrea were the focus of sedimentologic, stratigraphic and structural investigations. In the Bada area two mainly siliciclastic deposits informally called Ramude and Bada sequences were identified. The Miocene-Pliocene (?) Ramude sequence consists of conglomerates, lithic feldspathic arenites, siltstones and mudstones with a characteristic red color. The Ramude sequence was deposited in alluvial fan and more distal floodplain/overbank and lacustrine environments.

The overlying Pleistocene ? Bada sequence consists of conglomerates, sandstones, siltstones and mudstones plus minor bioclastic carbonates consisting of gastropods, ostracods and foraminifers. Environments of deposition of the Bada sequence range from fan delta to brackish lacustrine. Faults cutting basic sills and making contact between the two sequences indicate subsidence.

Sediments in the Dandero-Mahable area consist of conglomerate-sandstone, sandstone, and mudstone-sandstone lithofacies. They were deposited in alluvial fan, braided stream and ephemeral lacustrine environments. They are characterized by "couplets" of sandstone with mudstone-siltstone, which also alternate with gypsum. Gastropods and ostracods occur as fine calcareous beds.

In the Abdur area, the lithostratigraphy consists of the Buri sequence, the Abdur Volcanics, and the Abdur Reef Limestone. The Buri sequence consists of a siliciclastic-carbonate mixture of mudstones, limestones, sandstones, and conglomerates and in places ash and diatomite. They were deposited in fluvial, lacustrine and shallow marine environments. The age of the Buri sequence, which has been deformed and faulted, ranges from 0.90 Ma to 0.72 Ma. The Abdur Reef Limestone overlies unconformably the Buri Sequence and consists of a limestone complex of biostroms, bioherms and coral reef terraces. It has been dated at 0.125 Ma +/- 0.007 and was deposited during the latest Pleistocene transgression of the sea during the last interglacial (isotope stage 5e). Two samples of the Abdur volcanics were dated as 0.44 and 1.27 Ma, respectively.

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SPATIAL ARRANGEMENT OF DEFORMATION BANDS AND PROCESSES OF FORMATION WITHIN POROUS SANDSTONE: ARCHES NATIONAL PARK, UTAH

Timothy David Gibbons, MSGeoSci

The University of Texas at Austin , 2006

Supervisor: Randall Marrett

Individual deformation bands within porous sandstones reduce permeability and form barriers to fluid flow. A network of deformation bands can destroy reservoir connectivity and impose compartmentalization. Consequently, the spatial arrangement of deformation bands affects fluid flow within sandstone reservoirs, but it is unknown whether deformation bands occur at random locations or whether they follow systematic patterns.

This study, undertaken at Arches National Park , examined the spatial arrangement of deformation bands in the Moab Member of the Jurassic Entrada Sandstone. Field observations of this unit accurately quantified spatial relationships between deformation bands across 6 orders of magnitude (1 cm to 10 km). A 9.4-km-long scanline was constructed within the Moab Member, to measure spacing and orientation for individual deformation bands (N = 1467). Correlation count methodology was used to determine the spatial arrangement of deformation bands.

Correlation count analyses show that deformation bands within the Moab Member are natural fractals (self organized) at short length scales (cm to m). Although the spatial arrangement of deformation bands also is non-random at long length scales (m to km), spatial arrangement is not fractal (externally organized). Down-plunge projection shows that at long length scales, regions of abundant deformation bands correspond with hinge zones of subtle tectonic folds.

The fractal nature of deformation bands, evident at short-length scales, may be attributed to overall strain hardening during deformation band development. Deformation bands interact with one another due to strain hardening, and this results in spontaneous self organization. At long-length scales, deformation band occurrence is controlled by lateral variation in strain magnitude due to other deformation processes. Deformation bands are non-random in space, but the spatial organization is externally imposed.

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AGE AND CHARACTERIZATION OF THE RED HILLS PORPHYRY COPPER-MOLYBDENUM DEPOSIT AND ITS RELATIONSHIP TO THE CHINATI MOUNTAINS CALDERA, PRESIDIO COUNTY, TEXAS

Amy K. Gilmer, M. S. Geo. Sci.

The University of Texas at Austin, 2001

Supervisor: J. Richard Kyle

The Red Hills deposit in Presidio County, Texas, is the easternmost porphyry copper-molybdenum system in southwestern North America. The Red Hills intrusion is located approximately 1 km south of the 32 Ma Chinati Mountains caldera, and it has been postulated that the two may be genetically related. The quartz-monzonite porphyry intruded upper Permian limestones, sandstones, and siltstones of the Ross Mine and Mina Grande Formations, as well as sandstones and limestones of the Cretaceous Presidio Formation. Four distinct alteration types are recognized within the intrusion: potassic, phyllic, propylitic, and argillic. Mineralization within the sericitized stockwork porphyry consists of chalcopyrite, chalcocite, and molybdenite within quartz-pyrite veins. Sphalerite-bearing garnet skarn occurs as small replacement pods in the sedimentary rocks along the periphery of the intrusion.

Fluid inclusion studies of quartz veins associated with phyllic alteration indicate that the fluids associated with this stage had a mean temperature of 399 °C ± 58 °C based on measured homogenization temperatures. Scanning electron microscopy (SEM) combined with energy dispersive analysis (EDA) confirmed the presence of halite, sylvite, chalcopyrite, hematite, pyrite, and bixbyite daughter minerals within fluid inclusions.

Estimated salinities for the fluid inclusions from quartz veins associated with phyllic alteration range from 33 to 47 wt. % NaCl equiv. The high salinities of these fluids suggest a magmatic source. Measured homogenization temperatures and salinities for boiling assemblages were utilized to estimate pressure at the time of trapping and to provide constraints on their depth of formation. Pressure estimates based on contemporaneous trapping of immiscible fluids indicate a range of formation pressures from 20 to 30 MPa, corresponding to depths of formation of 2 to 3 km.

New U/Pb zircon age data and Re/Os molybdenite age data from the intrusion yield ages of 64.2 ± 0.2 Ma and 60.2 ± 0.3 Ma, respectively, indicating that the intrusion and mineralization are distinctly older than all other Tertiary magmatism (48 to 17 Ma) in Trans-Pecos Texas. The new ages also indicate that the Red Hills intrusion predates the 32 Ma formation of the Chinati Mountains caldera. Geochemical data from the porphyry further suggest no direct relationship to the Chinati Mountains magmatism. The Laramide age for the Red Hills porphyry makes it contemporaneous with the majority of the porphyry copper systems (75 to 54 Ma) in Arizona, New Mexico, and northern Mexico.

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SEISMIC AVO RESPONSE TO VARIATIONS IN SANDSTONE RESERVOIR PROPERTIES

Sharon Lee Goehring, M.S.

The University of Texas at Austin, 2005

Supervisor: Robert Tatham

Successful exploration for hydrocarbon reservoirs requires understanding seismic response for different sandstone lithologies. Today, many new targets lie within shale-rich environments such as mud-rich deltaic systems, on continental slopes or other basins with shaly mobile substrates. To produce reliable predictions, any ambiguities created by changing sandstone reservoir properties must be reduced. As both lithology and pore fluids significantly influence seismic response, correctly modeling prospects requires methods which can discriminate between these separate effects.

Evaluating amplitude variation with offset (AVO) permits identification of hydrocarbon reservoirs by their anomalous seismic response from background trends. This thesis tests empirical relationships between velocities and rock properties, effective media equations and Backus-averaging under several shaly-sandstone geometries ranging from pore-space clays to laminated sands and shales to successfully predict AVO response. Algorithms using the Hashin-Shtrikman equations for rock-strengthening pore-bridging clays and Backus-averaged laminae where shales reduce average acoustic impedance for the reservoir accurately modeled deepwater seismic data from the Gulf of Mexico. These two methods produce statistically significant models which reflect the seismic AVO response for varying sandstone properties.

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CORE STUDY AND SEQUENCE STRATIGRAPHIC ANALYSIS OF THE DESMOINESIAN BARKER CREEK ZONE, TABLE MESA AND RATTLESNAKE FIELDS, SAN JUAN COUNTY, NM

Alfred Dean Gomez, MSGeoSci

The University of Texas at Austin, 2003

Supervisors: Richard Buffler & William Fisher

162 pages, 50 references, 8 color plates in pocket

Over 750 ft (230 m) of slabbed Pennsylvanian (Desmoinesian (Barker Creek zone)) core and 150 thin sections, from the Table Mesa and Rattlesnake fields, San Juan County, New Mexico, were investigated to determine facies, depositional environment, sequence stratigraphy and hydrocarbon reservoir development. The fields are located on the Four Corners Platform low-angle shelf system, southeast of the Paradox Basin. Facies that were interpreted from the core are; non-skeletal packstone-grainstone, skeletal packstone-grainstone, chaetetid boundstone, porous algal grainstone-boundstone, calcareous siltstone, nodular wackestone-packstone, mud-rich algal mudstone-wackestone, oil-rich mudstone-wackestone, and black laminated mudstone. These facies are placed within a depositional environment model block diagram that was developed for the study area. Basinal and slope facies are interpreted to represent low to moderate relatively deep deposits and include the black laminated mudstone, oil-rich mudstone-wackestone, calcareous siltstone and nodular wackestone-grainstone. Overall the shoal water bank and local topographic high facies are the shallowest facies belts and represent moderate to high energy deposition, which include the non-skeletal, skeletal, chaetetid, porous algal, calcareous siltstone, and mud-rich algal facies. Proximal shelf facies are interpreted as moderately shallow moderate to high energy deposits. A Barker Creek zone sequence stratigraphic model was developed for the study area. Facies were packaged into eight high-frequency sequences based on depositional energy and base-level interpretations. High-frequency sequences were packaged into two high frequency sequence sets (lower and upper Barker Creek zone) using sequence stratigraphic stacking pattern and correlation tools. The lower and upper Barker Creek zones are each comprised of one transgressive and one highstand systems tract. Systems tracts are interpreted using aggradational, progradational, and retrogradational facies stacking patterns. Highstand systems tracts are subdivided into early and late highstand components in order to further determine the best timing for productive carbonate development within the study area. The sequence stratigraphic model indicates that the Barker Creek zone was dominated by highstand depositional conditions and that the thickest accumulations of carbonates occurred during late highstand. Reservoir analysis indicates that the porous algal facies is the primary, and best developed, hydrocarbon reservoir for the two fields, and was deposited during late highstand conditions along the shallow water bank facies belt.


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SENSITIVITY OF P-P, SH-SH AND P-SV SEISMIC REFLECTIVITY TO PARTIAL GAS SATURATION

Carmen Teresa Gómez, M.S. Geo. Sci.

The University of Texas at Austin, 2005

Supervisor: Robert Tatham

 P-P seismic reflectivity has been widely used as a tool to discriminate fully-water saturated rocks from fully gas saturated rocks. The sensitivity of seismic reflectivity to partial gas saturation, however, is still a topic of discussion and research.

Partial gas saturation occurs when the fluid filling the pore space of a rock is a mixture of gas and some liquid, such as oil or water. At some given pressure and temperature conditions, only a limited amount of gas can be dissolved in brine or oil. If more gas is available than the maximum that can be dissolved, then it is assumed that the excess gas will be distributed as gaseous bubbles. The scale of mixing of these gas bubbles and the liquid phase (oil or brine) will depend on rock permeability, viscosity of the fluids, capillarity forces, pore connectivity, fluid density contrast, and buoyancy of the gas. The effective P-wave seismic velocity will be higher for the coarse-scale mix than for the fine-scale mix of fluids. In the case of homogeneous fluid distribution, very low gas saturation may produce the same seismic response as a commercial gas accumulation (“fizz water” effect). That is why it is important to analyze the sensitivity of seismic reflectivity to the different properties of the rock and pore fluids to examine the real probabilities of different techniques to characterize gas saturation.

From sensitivity analyses, using Zoeppritz seismic reflectivity, I observe that PP reflectivities are more sensitive to density and P-wave velocity contrast for near-offsets and more to Poisson’s ratio at the far-offsets. The effects of density and P-wave velocity in P-P reflectivity follow each other very closely for most small angles of incidence. Thus, it is not possible in principle to separate the two effects. On the other hand, P-SV reflectivities appear to be nearly equally sensitive to velocity contrast, density contrast and Poisson’s ratio of the gas sand at near offsets. Sensitivity of P-SV reflectivity to density contrast is larger at angles of incidence between (30 and 60 degrees), in particular for fluid-fluid interfaces. Therefore, this far-offset range is where independent density information may be obtained by inversion of P-SV amplitudes. For SH-SH reflectivity, I find that the effect of density contrast is stronger in the 30 to 50 degree range of incidence angles.

Inversion techniques involving P-SV data using partial stacks over varying offsets seem promising to discriminate partial gas saturation. This is because they take into account the fact that the density effect on reflectivity separates from the seismic velocity effect only at mid- to large- offsets. Using larger offsets implies that approximations to Zoeppritz reflectivities, such as Aki and Richards (1980), are less accurate for these larger offsets ( > 35 degrees), in particular for P-S reflectivity. However, higher order approximations for P-S seismic amplitudes are impractical, since they are not linear with respect to seismic velocity and density contrasts (Larsen, 1999).

There is still not a generally accepted seismic reflection method to discriminate commercial gas concentrations from “fizz water” (low gas saturation) concentrations; however from the sensitivity analyses and the study of all the last techniques available, I conclude that the use of P-SV and SH-SH AVO, in addition to P-P AVO, is essential to understand this problem. Using good well calibrated multicomponent seismic data will be also a key element to solve this puzzle.

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STRATIGRAPHIC AND STRUCTURAL ANALYSIS OF THE NEOGENE SEDIMENTS OF THE OFFSHORE PORTION OF THE SALINA DEL ISTMO BASIN, SOUTHEASTERN MEXICO

Pedro Tomás Gómez-Cabrera, Ph.D.

The University of Texas at Austin, 2003 

Supervisors: William L. Fisher, Martin P. A. Jackson
274 pages, 208 references

Southeastern México has been affected by regional and local tectonic events. Regional tectonic events are the Gulf of México opening and the lateral movement of micro-plates on the Pacific margin. The local tectonic events are related to salt tectonics. Autochthonous Jurassic salt serves as the detachment level for the main compressional event in the late Miocene. Jurassic salt was allochthonously emplaced in the late Miocene, then partially displaced by a huge quantity of terrigenous sediments during the Plio-Pleistocene.

This research is a study of the main geological processes that have influenced the structural and stratigraphic evolution of the Neogene sediments in the offshore portion of the Salina del Istmo basin known as the Marbella area.

Owing to data availability, the project was divided into regional and local studies. The regional study is based on 2D multi-channel seismic reflection data, and the local study is based on a 3D seismic streamer survey.

Structural analysis in the regional study permits the recognition of four buried fold belts (Agua Dulce, Catemaco, Marbella, and Marbella Norte) trending roughly NE. These fold belts are the result of tectonic convergence in the pacific margin during late Miocene. The Agua Dulce and Marbella Norte fold belts are separated by an enormous salt withdrawal basin called the Pescadores basin. The Pescadores basin is bounded on the north by a spectacular stepped, counter-regional structure. Beyond the Pescadores basin, a salt mini-basin area is recognized in the upper continental slope. Another important structural element is the Sal Somera canopy in the southern part of the study area.

Sedimentation-rate analysis, based on isochore mapping in the local study area, indicates that from SB-2.4 to SB-2.6 Ma, deposition rate peaked with a maximum of 7.5 mm/yr.

Regional and local structural restorations show that, in general, the maximum allochthonous salt mobilization was during the Plio-Pleistocene because of the huge quantity of sediments that the Chiapas massif and the Sierra de Chiapas supplied to the basin. A geohistory plot indicates rapid basin deepening at 2.4 to 2.6 Ma, which is attributed to a major influx of sediments and allochthonous salt evacuation.

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CHARACTERIZATION OF THE SPATIAL ARRANGEMENT OF OPENING-MODE FRACTURES

Leonel Augusto Gomez Torres, Ph.D.

The University of Texas at Austin, 2007

Supervisor: Randall Marrett

In spite of the abundance of opening-mode fractures in the earth's upper crust, knowledge about their spatial arrangement remains limited. The spatial arrangement of fractures refers to the patterns of fracture positions in space. On one-dimensional analyses, fracture position can be obtained by combining fracture apertures, spacings, and their sequence along a one-dimensional scanline. Previous approaches failed to account for fracture position and fracture size, thus a new technique, normalized correlation count (NCC), was used to overcome these limitations. This technique was designed to distinguish random from non-random (fractal, inherited/imposed, periodically arranged fractures, or periodically arranged clusters) spatial arrangements of fractures. In addition, another method to quantify the attributes of microfractures in rock samples larger than a thin section was developed and used to quantify their spatial arrangements.

NCC indicated that where statistically significant (non-random) clusters exist, large fractures are more clustered than small ones. Differential clustering according to fracture size was detected in data sets from different lithologies at outcrop and rock-sample scale, suggesting that this phenomenon is related to development of fracture systems as opposed to host rock lithology and scale. Fracture clusters with power-law variation of spatial correlation with length scale are not strictly natural fractals because clusters occur in cascades at discrete values of length scale and not in a continuous fashion. Some statistically significant clusters with a power-law of spatial correlation are formed by smaller clusters with a power-law of spatial correlation that are also periodically arranged.

Fractures from the Cupido Fm. in the Monterrey salient were grouped in three categories based on their trace morphology, cement composition, and timing of fracture cements with respect to fracture opening. Fractures at outcrop scale in two of the categories exhibit low percentages of synkinematic cement and random arrangements, whereas fractures in the remaining category exhibit large amounts of synkinematic cement and periodically arranged clusters. An evolutionary model of fracture development based on subcritical propagation is proposed. This model suggests that mechanical layering increases during cluster development, explaining the non-random clustering within interclustering domains at outcrop scale and implies that cluster spacing increases with mechanical layering but decreases during evolution towards cluster saturation.

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CHRONOLOGY OF CENOZOIC TECTONIC EVENTS IN WESTERN VENEZUELA AND THE DUTCH ANTILLES BASED ON INTEGRATION OF OFFSHORE SEISMIC REFLECTION DATA AND ONLAND GEOLOGY

David Luke Gorney. M. S. Geo. Sci.

The University of Texas at Austin, 2005

Supervisor: Paul Mann

Newly acquired BOLIVAR seismic reflection data from offshore western Venezuela and the Dutch Antilles are combined with existing geologic and geophysical data sets to examine the complex chronology of tectonic events affecting the onshore Falcon basin and the adjacent offshore basins. This study also describes the seismic acquisition, processing, and interpretation methods applied to the BOLIVAR seismic reflection data and used in this study.

Three tectonic phases are constrained using these data: 1) Paleogene back-arc opening of the 3 to 6 km thick Falcon-Bonaire basin is the initial tectonic phase that occurred along east-west striking normal fault systems that have locally been inverted by later tectonic phases. These normal faults control the oldest depositional sequences and parallel the trend of the Bonaire basin. 2) northwest-striking normal faults crosscut these older normal faults and form deep submarine rifts that contain up to 4 km of sedimentary fill, forming deep water channels between the Dutch Antilles islands. Offshore well data and the age of onshore sediments in the Falcon basin indicate that this second phase rifting occurred in the late Oligocene through the early Miocene. 3) inversion of the Falcon basin commenced during the middle Miocene; this inversion phase is reflected in the present-day pattern of east-northeast-trending fold belt that can be traced over 200 km in the Falcon basin; a second fold-thrust belt (La Vela) can be traced over a distance of 175 km parallel to the Falcon coast; restoration of imbricate thrusts seen on seismic lines perpendicular to the Falcon coast indicates a minimum of 7 km of northeast-southwest directed thin-skinned shortening.

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PHYLOGENETIC INTERPRETATION OF EGGS AND EGGSHELLS AND ITS IMPLICATION FOR PALEOGNATHAE PHYLOGENY

Gerald Grellet-Tinner, M. S. Geo. Sci.

The University of Texas at Austin, 2001

Supervisor: Timothy Rowe

Our current knowledge of theropod phylogeny is based on skeletal morphology. Historically, paleontologists have valued data from skeletal elements as a source of characters for phylogenetic analysis. Eggs form under genetic control and should contain information regarding the evolutionary history of the group. Therefore, eggshells consisting of complex biopolymers and ionic crystals could be used in the same phylogenetic context as osteology. To date, no one yet has tried rigorously to classify eggs and eggshells in a phylogenetic context using cladistic analysis as a tool to establish an ancestor to descendant relationship.

My examination of previous literature revealed problems such as interpretation of eggs as trace fossils by previous researchers, their classification in a parataxonomic scheme, their misdiagnosis due to poor structural observations and their problematic association with parent lineage. By proposing to test the phylogenetic value of eggs and eggshells, I seek to address and resolve the above-mentioned problems. The choice of Paleognathae (ratites plus Tinamidae) was appropriate because the monophyly of this group has already been established based on osteological and molecular information, and also this group is well manageable by the number of taxa it contains. However, there are controversial aspects in the interrelationship of its members, and in the questionable assignment of Australian Dromornithidae to this clade.

My attempt to test the phylogenetic value of eggs (inclusive of egg morphology and eggshell structure) was based on the same precepts than any usual skeletal morphological based phylogenetic analysis. Characters and character states were searched, evaluated, scored in a matrix, and then run by a computer algorithm. The resulting trees were compared with existing molecular and skeletal based cladograms. In the process I had to modify and/or create new terms to describe oological characters.

My results support Paleognathae monophyly, and demonstrate Dromornithidae affinity with Neognathae. Minor differences exist among all the existing paleognath phylogenetic hypotheses, but these disparities could reasonably be argued for each analysis. Furthermore, oological characters permit the differentiation of groups at a generic level, thus validating the use of eggs and eggshells as a source of evolutionary characters.

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ALLUVIAL ARCHITECTURE AND TECTONIC SETTING OF THE MANGAS CONGLOMERATE, TYRONE MINE AREA, GRANT COUNTY, NEW MEXICO

Joy Deann Griffin, MSGeoSci

The University of Texas at Austin, 2001

Supervisor: Richard T. Buffler
.
The Mangas conglomerate is a Plio-Pleistocene syntectonic, extensional basin fill of the Mangas half-graben. The study area is located in the Mangas Valley in southwestern New Mexico at the juncture between the Rio Grande rift, the Mogollon-Datil volcanic province, and the Basin and Range. The study area straddles the Continental Divide on the eastern side of the Big Burro Mountains and includes excellent exposures of the conglomerate, making it an ideal location to study rift sedimentation.  


The Mangas half-graben forms a northwest-trending, down-dropped block between the Big Burro Mountains to the southwest and the Little Burro Mountains to the northeast. Erosion of these surrounding highlands during the late Neogene, probably Plio-Pleistocene, provided the source for as much as 370 m of Mangas conglomerate. The Mangas conglomerate is divided into the lower Mangas and the upper Mangas units. The division is based on provenance of the sediments and color. The lower Mangas was deposited in a large graben system, as sediment was eroded from the Big Burro Mountains and the Silver City Range to the north. Uplift of these Ranges controlled sedimentation patterns, creating punctuated influxes of matrix-supported, angular, poorly sorted, poorly stratified sands and conglomerates as basin margin alluvial fans. The processes controlling deposition of the fans were debris flows, streamfloods, and sheetfloods. 


After deposition of the lower Mangas, northwest-trending Basin and Range structures were reactivated. Uplift of the Little Burro Mountains along the northwest-trending Mangas fault bisected the large graben in which the lower Mangas was deposited, forming a local half-graben (Mangas half-graben). The upper Mangas was syndepositional with movement along the Mangas fault.  Localized, erosional fans cut into the lower Mangas along the footwall of the half-graben. The localized nature of deposition of the upper Mangas led to very poorly sorted, angular clasts deposited by debris flow processes. Paleosols identified in the upper and lower Mangas record periods of inactivity or nondeposition on the fans. A later episode of dip-slip movement postdating deposition is recorded by northeast-trending faults associated with the Burro Chief fault that offset both the upper and lower Mangas.

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LONG TERM SUBSIDENCE MONITORING USING SYNTHETIC APERTURE RADAR INTERFEROMETRY

Krishnavikas Gudipati, MSGeoSci

The University of Texas at Austin, 2003

Supervisor: Clark R. Wilson and Sean M. Buckley

78 pages, 36 references

This study is aimed at applying radar interferometry to investigate urban land subsidence. A least square method is applied in retrieving a deformation sequence from a database of Interferometric SAR images over Phoenix, Arizona. With the least squares method, short term interferograms can be used to generate a chronologically ordered sequence of deformation and its evolution.

Synthetic Aperture Radar Interferometry (InSAR) is a satellite based radar technique developed over the past two decades and has been widely applied in various research fields related to earth sciences. It has been successfully applied in topographic mapping, earthquake studies, monitoring volcano deformation, and more recently for land surface deformations for subsidence monitoring. The most important source of error in InSAR is temporal decorrelation (i.e. loss of information due to differences in backscattered signal between the two images). The Phoenix metropolitan area in Arizona lies in broad alluvial valleys or basins surrounded by mountainous terrain of consolidated sedimentary rocks. The permeable alluvial valleys are capable of storing large quantities of groundwater. Groundwater pumping resulting from rapid urbanization and increases in agricultural and industrial water usage has caused land subsidence in the region. In all three subsidence features were studied located in the cities of Peoria, Glendale and Scottsdale.

InSAR features associated with the subsidence show larger signatures with progressive time spans. Deformation images obtained as a time series indicate the presence of non-linear trends in subsidence rates. At Peoria and Glendale, subsidence rates showed a seasonal variation and the subsidence was highly correlated with the declining water table levels. Decline in subsidence rates in was seen at Scottsdale between 1996 and 2000.

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TEMPORAL AND SPATIAL CONTROLS ON CAVE WATER AND SPELEOTHEM CALCITE ISOTOPIC AND ELEMENTAL CHEMISTRY, CENTRAL TEXAS

Amber Lee Guilfoyle, M.S. Geo. Sci.

The University of Texas at Austin , 2006

Supervisor: Jay L. Banner

The isotopic and elemental composition of speleothem calcite precipitated from dripwaters in caves have been used to elucidate changes in karst groundwater flow paths and changes in climate such as shifts in vegetation and rainfall patterns. Given that recent studies have shown seasonal isotopic and elemental changes in cave dripwater chemistry, then these changes are most likely reflected in the precipitated calcite. This affirms the need to study the environmental controls on the dripwater isotopic and elemental chemistry on seasonal time scales, since ultimately these are environmental controls on the precipitated speleothem calcite. In this study, physical, chemical, and meteorological variations at 13 drip-water and pool sites in two cave systems in the Edwards aquifer of central Texas are used to delineate the controls on the evolution of cave waters. The chemical evolution of these cave waters can be accounted for by variations in calcite precipitation, soil geochemistry, flow paths, and degassing of CO 2 driven by seasonal overturn of the cave atmosphere.

Calcite precipitated on glass substrates placed under three of the thirteen dripwaters in this study was analyzed for its C and O isotopic composition in order to assess 1) seasonal variations in the isotopic composition and 2) the extent to which precipitation occurs in isotopic equilibrium with its host dripwater. Each winter season, calcite growth rates increase, which corresponds to changes in the C and O isotopic composition of the calcite: higher d 13 C and d 18 O values during winter and lower d 13 C and d 18 O values during summer. Some calcite samples were found to precipitate out of C and O isotopic equilibrium, with maximum departures of 1.3‰ with respect to carbon and 1.4‰ with respect to oxygen. The results show that d 13 C and d 18 O in the modern speleothem calcite: 1) can vary sub-annually without change in vegetation or climate, and 2) reflect in the majority of cases precipitation out of isotopic equilibrium with the host dripwater that precipitates the calcites.

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COMPLETE ANISOTROPIC ANALYSIS OF THREE COMPONENT SEISMIC DATA RELATED TO THE MARINE ENVIRONMENT AND COMPARISON TO NINE COMPONENT LAND SEISMIC DATA

Jason Ethan Gumble, Ph.D.

The University of Texas at Austin , 2006

Supervisor: Robert H. Tatham

To facilitate the transfer of knowledge from one arena to another, a comparison between nine component, controlled polarization shear-wave land seismic data and three component mode converted seismic shear-wave data was made. The continuing movement of petroleum exploration into the offshore arena and the increasing number of aging offshore oil fields may necessitate the use of shear wave data for full characterization of reservoir properties for finding, characterizing, and prolonging the life of the oil fields through the description of anisotropy as an analog for rock properties. Operationally limited to the use of compressional seismic sources in the marine environment, mode-converted shear-wave data recorded by three component seismic receivers must be exploited to arrive at full characterization of anisotropy.

Effective media theory, seismic modeling, and post stack analysis including four component matrix rotations and numerous other tools developed on land were adapted and used offshore. A full understanding of anisotropy, shear wave birefringence and polarization was required to evaluate the similarities and differences between direct shear waves and mode converted shear waves. The investigation of seismic anisotropy related to shear waves began with the Cymric Oil field in California , progressed out into shallow waters of the Gulf of Mexico to the Teal South Oil Field, and finished in the Williston Basin, Saskatchewan, Canada. It has been revealed that not only can lessons be learned from the historical practice of nine component seismic analysis on land and applied to the marine environment, but that also the reverse is true. The use of full azimuth, full offset data and prestack analysis was developed and has served to extend present day anisotropic analysis beyond its current limitation of 1D application. Pre-stack converted shear-wave layer stripping analysis techniques developed include extraction of a azimuthal and offset variant time-shifts for birefringence correction, as well as the analysis of azimuthal and offset variance in amplitudes and reflected polarization. A numerical comparison between controlled source polarization, direct shear-waves and uncontrolled source polarization, mode converted waves, led to a correction for apparent polarization effects on the direct shear-waves and a correction for incomplete acquisition geometry for mode-converted waves.

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HIGH RESOLUTION SEQUENCE STRATIGRAPHY OF THE CRETACEOUS WOODBINE FORMATION, HENDERSON AND NAVARRO COUNTIES, TEXAS

Russell Royden Hamman, M. S. Geo Sci.

The University of Texas at Austin, 2001

Supervisor: William L. Fisher


The terrigenous clastic Woodbine Formation is one of several progradational intervals in the East Texas Basin. It is also a prolific hydrocarbon producing horizon that accounts for almost 80% of the cumulative oil production from the East Texas Basin.

Sediments comprising the Freestone Delta Member of the Woodbine Formation average 650 feet thick in Henderson and Navarro Counties. Within the study area, four marine shale bounded parasequence sets have been identified based on changes in sand body stacking patterns and log signatures. These parasequence sets are each built from at least two parasequences as determined through facies mapping. Each parasequence consists of three principal sandy facies building blocks with unique log signatures and orientations: fluvial or distributary channel fills, channel mouth bars, and strandplains. The fluvial and distributary channel-fill sand bodies are dip oriented and show a upward fining signature. The channel-mouth bar facies is also dip oriented but displays a coarsening and then upward fining log signature. Strike-oriented sand bodies with uniform to upward coarsening vertical trends compose the strandplain facies. The channel-mouth bar facies is typically rare in wave dominated delta systems like the Woodbine but serves to define the sediment supply axes for each parasequence.

Two dip-oriented sediment supply axes controlled sediment deposition. Theses axes have distinct depositional histories that are reflected in vertical and lateral depositional system changes throughout the Woodbine Formation. The lowermost parasequence recorded a sand-rich shoreface environment that evolved into a proximal fluvial setting due to a presumed decrease in accommodation space. Above this constructional fluvial and shoreface interval, the sedimentary system retrograded to shelf and distal deltaic depositional systems in the upper, middle Woodbine Formation. However, rejuvenated progradation of strandplains and associated channel fills occurred in the uppermost parasequence set.

Sediment supply varied between northwestern and northeastern axes in the lower and middle Woodbine but was exclusively a northwestern source in the uppermost parasequence set.

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LATE QUATERNARY SEISMIC STRATIGRAPHY AND STRUCTURE OF THE WESTERN INSULAR SHELF MARGIN OF PUERTO RICO

Martín Hanzlík-Valentín. M.S. Geo. Sci

The University of Texas at Austin , 2006

Supervisor: Paul Mann

The modern insular shelf and slope of western Puerto Rico is characterized by reef carbonate and siliciclastic sedimentary environments controlled by the complex interplay of tectonic arching and faulting, vigorous erosion of the elevated island of Puerto Rico, fluvial incision and sedimentation pulses, reef growth, and rapid late Quaternary eustatic sea-level changes. For this study, I interpret 725 km of high-resolution, single-channel seismic lines that were collected over the western insular shelf and slope by the RV Isla Magueyes in 2000 to better understand tectonic, erosional, and eustatic controls on late Quaternary history.

The seafloor geology of the western shelf and slope area of Puerto Rico has been well studied and mapped mainly from grab and short cores collected by geoscientists at the U.S. Geological Survey and at the University of Puerto Rico at Mayagüez. Because of low tectonic uplift rates from the western coast of Puerto Rico , the onland late Quaternary sedimentary history is not recorded in Quaternary coastal outcrops. The results of my seismic interpretation and correlation with multi-channel seismic data collected in 1972, reveal four main units defined by characteristic stratal reflection terminations and seismic facies. These units include: Unit 1 (basement) - a gently folded and faulted basal section correlated to the Oligocene-early Pleistocene carbonate shelf of Puerto Rico; deeper penetration, industry multi-channel seismic lines show that these rocks are deformed in a broad east-west-trending arch; Unit 2 (lowstand systems tract, LST) - chaotic channel fill deposits filling deep (~ 30 meter) incisions formed during the Last Glacial Maximum about 20 ka; Unit 3 (transgressive system tract, TST) - poorly stratified deposits truncating the top of Unit 2 and deposited during early Holocene transgression of the shelf margin; Unit 4 (highstand system tract, HST) – late Holocene, highly stratified deposits related to aggradation as the Holocene transgression began to slow. The base of unit 4 is a downlap surface interpreted as a maximum flooding surface likely formed about 8 ka. East-northeast-striking faults are observed that offset the late Quaternary units in three separate zones off the west coast of Puerto Rico . Because of a lack of wells and long cores from the shelf and slope area, age estimates for the four units are based on correlations with sea-level curves derived from dated coral samples in the Caribbean and western Atlantic region. All four units are deformed by faulting that should be considered active and possibly hazardous for the rapidly developing west coast of Puerto Rico . In one area, a large, late Holocene slump (~ 0.016 km 3 ) is mapped using seismic, sidescan sonar and bathymetric data. Onland continuations of these faults are likely, but have not been identified due to cultural overprint of natural scarps on late Quaternary floodplains.

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ANALYSIS OF FRACTURE CLUSTERING USING THE WAVELET TRANSFORM: AN EXAMPLE FROM THE MARBLE FALLS LIMESTONE

Christopher Matthew Hare, M.S. Geo.Sci.

The University of Texas at Austin, 2002

Supervisor: Randall Marrett

Characterizing the spatial arrangement of fractures is currently of interest when attempting to solve a range of geologic problems, such as fluid flow through fractured aquifers and petroleum reservoirs. Realizing that fractures can significantly affect the magnitude of a rock's permeability and control the preferred orientation of fluid flow, understanding the geometry of fracture patterns within a rock volume is necessary in order to correctly characterize the often heterogeneous behavior of the system.

Fracture data analyzed in this project were collected at Pedernales Falls State Park, near Johnson City, TX from the Marble Falls Limestone. The scanline data from Pedernales Falls consist of kinematic aperture and position measurements for 999 calcite filled veins, over a scanline length of approximately 59 meters that was oriented perpendicular to the strike of the subvertical fractures. Although the aperture values follow a power-law, the spacing values are best fit by a log-normal distribution and suggest a nearly random spatial pattern.

Current methods of spatial analysis of fracture data are limited in that the sequence of fracture spacing values is often ignored by the actual analysis. This project applies techniques of wavelet analysis in a new manner in order to test the hypothesis that the fractures at Pedernales Falls State Park are arranged spatially into non-random clusters. Analysis of the Pedernales data shows that clusters exist at multiple scales and suggests that the larger fracture clusters are made of smaller fracture clusters, and so on. This multi-scaled arrangement provides a basis for the proposal of a fractal distribution of the fracture clusters at Pedernales Falls. The multi-scaled pattern of the fracture clusters is readily analyzed by wavelet techniques which take into account position (i.e. translation along the scanline), as well as the scale of observation (i.e. the dilation of the analyzing wavelet). This new method of analysis allows for both the size and position of the fractures to be analyzed simultaneously, something that was previously unattainable using traditional techniques.

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DEFORMATION OF BLOCKS AND MATRIX IN FRANCISCAN MELANGE, SAN SIMEON, CALIFORNIA: IMPLICATIONS FOR MELANGE GENESIS

Daniel F. Harrington, M.S. Geo. Sci.

The University of Texas at Austin, December, 2001

Supervisor: Mark Cloos

Superior exposure of blueschist-bearing Franciscan subduction melange exists along 4 km of seacliffs south of San Simeon, CA. The melange's chaotic fabric, inclusions of variegated lithologies, and generation and emplacement have been alternately ascribed to dominantly sedimentary or tectonic processes in previous studies.

The melange "matrix" is a fine-grained (<20 micron) black metapelite, and bears a foliation which is generally parallel to the margins of elongate melange blocks and dips ~60° to the northeast. The foliation is defined by a pervasive network of anastomosing scaly cleavage planes.

Greywacke inclusions are lenticular, and display pinch-and-swell and boudinage geometries and high (4 -12+) aspect ratios from outcrop to thin-section scale. The greywacke is 50-70% clay-sized material ("groundmass", comprising detrital matrix and authigenic clays). Detrital quartz, plagioclase, and rare K-feldspar are surrounded by groundmass, and are rounded and optically appear relatively unstrained. SEM-CL analysis reveals cryptic fracturing in quartz grains in excess of that apparent in quartz grains from a local trench-slope basin greywacke.

Mafic greenstone and blueschist inclusions display similar pinch-and-swell and boudin shapes, with aspect ratios as high as ~20. Inclusions of both types contain small (1 mm - 3 cm) pieces of relatively undeformed rock set within fine-grained (<0.3 mm) cataclastic material which is concentrated along intra-inclusion fractures, inclusion edges, and necks. Cataclastic texture is more pervasive in smaller inclusions and in those with higher aspect ratios.

Observations are consistent with a tectonically-driven process of melange formation. The majority of strain was accommodated by flow in the underconsolidated pelitic matrix, separating and dispersing included blocks. Internal block deformation was accommodated by particulate flow (grain-boundary sliding and rotation) in the greywacke groundmass and by cataclastic flow in greenstone and blueschist. Particulate and cataclastic flow mechanisms are manifestations of high fluid pressure conditions that were maintained throughout the deformational history. Cataclasis was concentrated along block margins, and was induced by interaction with the ductile matrix, and assisted by chemical alteration of crystalline material. The scaly cleavage in the matrix formed late, after the blocks were chaotically mixed, during offscraping and final dewatering. Prior to offscraping, shear strains within the subduction channel that caused distortion and dispersion were on the order of 1000s.

The grain-scale textures which indicate particulate flow in the greywacke and cataclastic flow in the crystalline inclusions are preserved in the melange at San Simeon because the material has remained unheated and untectonized since its emplacement; heating in excess of ~200°C would have obliterated most of the textures described in this study.

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STRATIGRAPHIC AND STRUCTURAL CONTROLS OF PERMIAN CARBONATE-HOSTED SILVER (PB-ZN) MINERALIZATION, SHAFTER, PRESIDIO COUNTY, TEXAS

Jennifer Adair Head, M.S.

The University of Texas at Austin, 2002

Supervisor: J. Richard Kyle

The Presidio deposit at Shafter, Texas, produced 35 million ounces of silver from 1882 to 1942, along with lead and minor gold. The production and estimated reserves of 20 to 30 million ounces makes this manto-type replacement deposit the largest silver deposit in Texas. The complex structural history of the Shafter area caused the host Permian Mina Grande limestones to be fractured repeatedly along different trends. Fractures that appear to control mineralization are related to the following: Mid-Tertiary Chinati Mountains caldera uplift, regional N-NW Texas Lineament and W Chalk Draw fault structures, and NE structures that have no regional equivalents.

The host Mina Grande carbonates can be divided into the Massive, Pseudobreccia and Basal facies. The Massive facies that lies directly below the Permian-Cretaceous unconformity is a completely dolomitized unit in which no original structures or fabrics are apparent. The Pseudobreccia facies consists of a zone in which "clasts" of original limestone occur in a matrix of orange stained dolomite due to partial dolomitization of the strata. The Basal facies is an unaltered limestone (wackestone to packstone) or only slightly dolomitized unit that forms the unit directly overlying the Ross Mine Formation.

The Mina Grande has had a complex diagenetic history that sufficiently prepared the rocks for hydrothermal mineralization. The history starts with the deposition of Mina Grande limestone as forereef facies, wackestone to packstone with abundant crinoid, fusulinid, bryozoa and brachiopod fragments. The limestones then underwent early marine and freshwater cementation (Stage-I calcite), followed by burial and early dolomitization (Stage-I dolomite). The burial also caused compaction producing micro-fractures and neomorphism of the limestone. Post-Permian uplift resulted in karstification of the Mina Grande with associated dedolomitization and dolomite dissolution. Subsequent burial during the early Cretaceous produced a second stage of dolomite (Stage-II dolomite). A second stage of calcite was also precipitated during the reburial (Stage-II calcite). During this time the karst cavities created during post-Permian uplift were filled with clay. Laramide- and Chinati Mountains caldera- related tectonic activities in late Cretaceous to middle Tertiary fractured the Mina Grande. These fractures and diagenetic porosity zones provided conduits for hydrothermal solutions that deposited calcite, quartz and Ag-Pb-Zn sulfides (Stage-III calcite and quartz). Late stage meteoric water infiltration resulted in oxidation of the sulfide ore to produce the present silver deposit. A post-oxidation calcite was then precipitated in remaining pores and fractures.

However, not all locations within the Mina Grande have had extensive porosity development. Compared to the Presidio and Shafter deposit areas, the Mina Grande Formation to the west (e.g. Perry Mine Hill) does not have significant porosity development in the form of karst and/or the altered Massive and Pseudobreccia facies. These locations are composed of the lower porosity Basal facies. This lack of extensive porosity development in the form of karst or the Massive and Pseudobreccia facies may explain why these locations do not host any stratabound ore units like the Presidio and Shafter deposits. The development of karst and/or the Massive and Pseudobreccia facies with the higher porosity is the controlling factor for the localization of stratabound deposits. In locations lacking sufficient porosity mineralization is confined to fractures.

Structural trends in the Shafter area control the distribution of mineralization. The Mina Grande fault zone and associated en echelon faults control the distribution of the mineralized zones within the Presidio Mine. Ore fluids rose from depth along these faults and migrated into the fractured Mina Grande. Both the faults controlling mineralization and the mineralization itself may be the result of a large igneous intrusion at depth. A complex diagenetic history of the Mina Grande allowed for sufficient preparation creating channels for fluid flow through karst features and the creation of pore space. This preparation along with the highly fractured nature of the Mina Grande limestone focused the hydrothermal mineralization and subsequent oxidation. Within the Presidio/Shafter deposit, structures within the Mina Grande formation, including the Mina Grande fault and en echelon faults, appear to have served as the conduits for fluid flow from depth. Well-developed Massive and Pseudobreccia facies (oriented N60E beneath the Cretaceous unconformity) with high karst-related porosity controlled where the fluids migrated into the formation and therefore the locations of the replacement deposits.

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RESERVOIR TRENDS AND EXPLORATION POTENTIAL OF THE EL VADO SANDSTONE MEMBER OF THE MANCOS SHALE, NORTHWESTERN NEW MEXICO

Tiffany Setare Hedayati, M.S. Geo. Sci.

The University of Texas at Austin, 2008

Supervisor: Lesli J. Wood

The El Vado Sandstone Member (late Coniacian) of the Mancos Shale is considered by many to be an important unconventional hydrocarbon resource target (Ridgley, 2001) in the San Juan Basin, located in northwestern New Mexico. The shelf sandstones of the El Vado were deposited along the western margin of the Western Interior Cretaceous Seaway. The El Vado is part of a transgressive-regressive wedge of rock that overlies a large, older transgressive wedge which contains the Tocito Sandstone (the largest oil producer in the basin). Despite its productivity in parts of the basin, the nature, origin, and distribution of the El Vado Sandstone is poorly understood.

Using well logs and core data, the subsurface has been mapped to illustrate the distribution of the El Vado Sandstone across its extent in the San Juan Basin. The El Vado is reflected in logs as a thick (~ 120 foot) interval of low gamma ray and high resistivity. The gamma ray log character reflects highly laminated sand-to-silts interbedded with shales. A total of 13 cross sections were constructed based on the high density of well log control. Isopach maps were then generated for the entire interval and individual cycles of the El Vado. Regional net sand and net-to-gross maps, determined from 104 digitized well logs, highlight the regional distribution of sand content.

Two regions in the basin were examined in outcrop, the northeast and the southeast. In the northern outcrops, the El Vado consists of five cycles of similar thickness (~ 4 m each) separated by marine shales with cycles becoming progressively sandier upward. To the south, the El Vado Sandstone appears to transition from a shelf deposited sandstone into a lower shoreface sandstone.

Examining the El Vado Sandstone in the subsurface and in outcrops helped the author to improve the understanding of the nature and distribution of the sands throughout the basin.

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HYDROGEOLOGY OF HETEROGEONOUS ALLUVIUM IN THE LEONA AQUIFER, CALDWELL COUNTY, TEXAS

Lloyd Harrison Hemphill, M.S. Geo. Sci.

The University of Texas at Austin, 2005

Supervisor: John M. Sharp, Jr.

The Leona aquifer is an important, but overlooked, water resource in Central Texas. The Quaternary Leona Formation occurs as several isolated alluvial deposits at the margins of the Edwards Plateau. Each of these deposits forms an aquifer. One of these aquifers is located near Lockhart, Texas. This aquifer is recharged by infiltration of precipitation and is discharged by numerous springs and seeps. Additional sources of discharge are evapotranspiration and cross-formational flow into the Wilcox aquifer. The saturated thickness at this location varies seasonally but is rarely greater than 3 m (10 ft).

Groundwater flow in an aquifer of this scale is influenced by its heterogeneous nature. This research identified seven different facies in the Leona Formation and the underlying Wilcox Group. These divisions were based on sediment classification, lithology, and sedimentary structures. The Leona Formation is covered by sandy and silty clay soil and caliche. Each of these facies has different hydraulic properties.

Many empirical relationships between grain size distribution and hydraulic conductivity (K) have been discussed in the literature. Equations developed by Hazen, Slichter, Terzaghi, Beyer, Saurbrei, and Kozeny were used to estimate hydraulic conductivity. Hydraulic conductivity was also measured in the laboratory with constant and falling head permeameters. Hydraulic conductivity of the Leona aquifer varies seven orders of magnitude. Hydraulic conductivity varies up to four orders of magnitude within a single facies due to small-scale differences in grain size distribution and degree of cementation. The arithmetic mean of hydraulic conductivity in vertical profiles through the Leona aquifer ranges from 0.013 cm/sec (37 ft/day) to 0.14 cm/sec (397 ft/day).

Water quality is a concern for many unconfined shallow alluvial aquifers, including the Leona aquifer. Elevated nitrate levels indicate contamination resulting from agricultural landuse. Nitrate concentration in the Leona aquifer ranges from 4 ppm nitrate as NO 3 to greater than 70 ppm nitrate as NO 3. These concentrations are significantly greater than those observed in the Wilcox aquifer.

The U.S. Geologic Survey computer code MODFLOW was used to create a groundwater model of the Leona aquifer. In the best simulation, specific yield was 0.1 and horizontal hydraulic conductivity was 0.058 cm/sec (164 ft/day). The simulated hydraulic conductivity is an order of magnitude less than observed in gravel pit outcrops. Modeled recharge was 9 percent of annual precipitation in 2003 and 20 percent of precipitation in the first six months of 2004. Five hypothetical wells were placed in the model to examine the effects of pumping on the aquifer. Wells pumped for 61 days at 0.04 l/sec (0.6 gpm) cause insignificant drawdown while wells pumped at a rate of 3.5 l/sec (55 gpm) cause up to 0.55 m (1.8 ft) of drawdown. Natural drainage of the aquifer caused the water table to decline 0.8 m (2.6 ft) over this same period. MODPATH simulations using this groundwater model indicate an average residence time in the aquifer of 13 years and a maximum residence time of 70 years.


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ANALYZING DEEP-WATER NEAR SEAFLOOR GEOLOGY WITH CHIRP SONAR SUB-BOTTOM PROFILES: GREEN CANYON GULF OF MEXICO

Jaime Hernandez. M.S. Geo. Sci.

The University of Texas at Austin , 2006

Supervisor: William Fisher

The study area is located on the continental slope in the Green Canyon deep-water area of the Gulf of Mexico . This area is being investigated by the Bureau of Economic Geology as part of several active gas hydrate studies across the area. The chirp sonar profiles used in my study were collected with an Autonomous Underwater Vehicle (AUV) utilizing a frequency-modulated seismic (sonar) source that emitted a 2 to 8 kHz sweep (chirp) frequency signal (wavelengths less than 2 meters ). The recording time is limited to about 50 milliseconds , with time zero occurring at the altitude of the AUV about 50 meters above the seafloor. The signal images to about 40 meters below the seafloor, and profiles are as long as 5 km . An interpretation of deep-water, near sea-floor geology has been conducted using both chirp sonar profiles and multibeam bathymetry.

Seismic reflections from within the shallow sediments are caused primarily by contrasts in density, rather than acoustic velocity. Reflections were successfully simulated using a model with a constant velocity of 1560 m/s and densities of 2.1 g/cc for sand, 1.4 g/cc for mud, and 1.7 g/cc for silty sand.

The chirp sonar profiles imaged near-seafloor geology at nearly a meter scale and allowed for detailed interpretation. The interaction of soft sediment deformation, creep movement and neo-tectonic activity related to gas expulsion controlled the actual topography of the sea-floor.

The geologic time represented in the 50 milliseconds of chirp data recorded with the AUV, which is about 40 meters of depth, is approximately 0.050 Ma . B.P., consistent with a depositional rate of 0.8 meters per 1000 years . Reflection patterns are interpreted to be related to fluctuations in sea level. High reflectivities (density contrasts) are interpreted to be deposited during the last sea level low stand, and low reflectivities are interpreted as sedimentation during the last high stand. Sediments deposited during the low stand are proximal while others are distal, deposited in deeper water environments.

Shallow structures observed in the chirp sonar profiles are mainly related to gas mobilization mechanisms, which shaped the topography of the seafloor in conjunction with soft sediment deformation and creep movement.

The geomorphic features are related in some cases to gas expulsion zones such as pockmarks and mud volcanoes. Other structures are related to soft sediment deformation and creep mobilization. Soft sediment deformation is confined to the deepest part of the minibasin, while the other features are not depth dependent. Highly deformed intervals at the bottom of the sequence seem to control subsequent sedimentation.

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VERTICAL RESOLUTION OF SHEAR-WAVE VELOCITY INVERTED FROM PRE-STACK P-WAVE SEISMIC AMPLITUDE AND OFFSET MEASUREMENTS: NUMERICAL SENSITIVITY ANALYSES APPLIED TO THE ONADO FIELD, EASTERN VENEZUELAN BASIN

Rodolfo Carlos Hernández, M.S.Geo.Sci.

The University of Texas at Austin, 2008

Co-supervisors: William L. Fisher and Carlos Torres-Verdín

Pre-stack P-wave seismic amplitude and offset inversion was conducted on a data set synthesized for the Onado oil field located in the Eastern Venezuelan Basin. The objective was to quantify the vertical resolution of the inverted shear-wave velocity (Vs) as a function of angle of incidence. Post- and pre-stack seismic P-wave data were used to extract the wavelets necessary to simulate seismic amplitude measurements via Zoeppritz’ equations. Two sets of synthesized data were used in the sensitivity analysis. The first set consisted of three different angle-range stacks comprising single-angle stacks (2°, 3°, 4°,…, 24°, 25°), three narrow angle-range stacks ([2°-4°], [4°-6°],..., [22°-24°], [24°-26°]), and five wider angle-range stacks ([2°-6°], [6°-10°],..., [18°-22°], [22°-26°]). The second set incorporated partial-angle stack models comprising an increase of maximum angle ([2°-3°], [2°-4°],..., [2°-24°], [2°-25°]), and an increase of the maximum in every five angles ([5°-10°], [5°-15°],..., [5°-30°], [5°-35°]).

Pre-stack inversion was performed on all the synthetic data sets using commercial simultaneous inversion algorithms. Vs inverted logs were derived from data synthesized at a key well and correlated with the actual measured Vs logs for the sensitivity analysis. Detailed analysis shows a general trend in the vertical resolution with increasing maximum angle for all stacks, with a progressive increase in vertical resolution (effective angle interval) from the lowest angle to a maximum range between 15° and 20° (critical point), and a subsequent decrease for farther angle data available (non-effective angle interval). This general trend enabled the selection of the largest angle to be included in the pre-stack inversion analysis. Partial-angle stacks entail a progressive gain in vertical resolution within the effective interval of incidence angles. Angle-range stacks, on the other hand, entail a more variable behavior with local lows. The difference between both data sets is attributed to the fact that the information borne by partial-angle stacks increases with an increase of angle, whereas angle-range stacks include information specific to only the associated angle interval.

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PEGMATITE-CONTAINING SHEAR ZONES: A MECHANISM FOR THE FORMATION OF ISOLATED FELDSPAR AUGEN MEGACRYSTS AT WILLIMANTIC DOME, CENTRAL CONNECTICUT

Katherine Anne Herrell, MS

The University of Texas at Austin, 2002

Supervisors: Sharon Mosher, William Carlson

Large, isolated feldspar augen (12.0 to 0.5 cm) in quartzofeldspathic shear zones can be the product of intense disaggregation of pegmatites. Such augen are commonly interpreted as original porphyroclasts or porphyroblasts. The pegmatite-disaggregation mechanism of forming isolated feldspar augen is documented by pegmatites that underwent extension and thinning under amphibolite facies conditions in a low-angle ductile normal fault at the basement-cover contact of the Willimantic dome, eastern Connecticut. Field relations illustrate a laterally progressive disaggregation and boudinage of pegmatite layers. Intact pegmatites containing large feldspar augen surrounded by recrystallized pegmatite gradually disassociate, forming strands of floating feldspar augen connected by very thin layers of recrystallized quartzofeldspathic material parallel to the dominant foliation. The final separation and attenuation of these thin connective layers results in completely isolated, individual feldspars that mimic the geometry of a porphyroblast or porphyroclast with a recrystallized tail. Thin-section observations indicate that these "isolated" feldspars are still connected by slip surfaces and micro-scale lenses of recrystallized quartzofeldspathic material. These slip surfaces provide conduits for the migration of fluids that promote grain softening and recrystallization of the feldspars. Feldspar grains within single sheared pegmatite strands vary dramatically in their degree of deformation and recrystallization. Largely undeformed, intact crystals with little to no recrystallization occur alongside oblate, completely recrystallized grains. Less-deformed augen commonly contain kink bands or bent lattices that have localized partial to complete rotational recrystallization. Other augen are rimmed by rotationally recrystallized grains and deformation-induced myrmekite. The degree of internal deformation and recrystallization that each grain displays relates directly to its original orientation and the amount of locally present quartz. This mechanism for the formation of large, isolated feldspar augen through fluid-assisted pegmatite disaggregation may be common and should be considered when studying other shear zones. Such augen can be distinguished from porphyroclasts or porphyroblasts by their large size, aggregate character, lack of inclusion trails, and relict connections between grains.

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CONTROLS ON SCALES OF CHEMICAL EQUILIBRATION DURING METAMORPHISM: INSIGHTS FROM GARNET ZONING PATTERNS

James Dwight Hixon, M.S.Geo.Sci.

The University of Texas at Austin, 2006

Supervisor: William D. Carlson

Garnets in metapelites from Harpswell Neck, Maine display atypical compositional zoning patterns that reveal the effects of unusual fluid compositions on rates of intergranular diffusion and scales of chemical equilibration during garnet growth.

At Harpswell Neck, pelitic rocks metamorphosed to 525-575 °C and 0.2-0.3 GPa contain chlorite + biotite + muscovite + garnet + quartz + plagioclase + ilmenite ± graphite ± pyrrhotite ± pyrite ± chalcopyrite. Garnet crystals display a wide variety of unusual patterns of compositional zoning. Mn is commonly concentrated in multiple isolated patches in the interior of garnet; this effect is superimposed on the more common tendency for Mn to partition into garnet cores during early stages of growth. Fe and Mg exhibit patterns of compositional zoning inverse to those of Mn. Ca concentration is slightly elevated or flat in garnet interiors and increases in concentric annuli near garnet rims. Y concentrations are highest in garnet cores and in concentric annuli near garnet rims.

Relative rates of intergranular diffusion can be interpreted from these garnet compositional zoning patterns. Isolated, patchy zoning of Mn, Fe, and Mg is interpreted as overprint zoning, indicating very slow rates of intergranular diffusion for these elements. In contrast, Ca and Y display patterns of higher core concentrations and concentric rings, which indicate that these elements achieved rock-wide chemical equilibrium. The observed combination of zoning patterns and inferred length scales of diffusion are not compatible with prior models in which temperature is the dominant factor controlling relative rates of intergranular diffusion.

The composition of intergranular fluid affects the solubility of elements during metamorphism, thereby exerting a fundamental control on rates of intergranular diffusion and scales of chemical equilibration. To explain observed garnet compositional patterns, the intergranular fluid would need to produce high solubility for Ca and Y and low solubility of Mn, Fe, and Mg. Limited data on solubility suggest that a fluid poor in Cl- and F-, but rich in SCO42-, is likely to have these effects; such a fluid might be generated by de-sulfidation of pyrite to pyrrhotite, or oxidation of pyrite and pyrrhotite during metamorphism, or both. Direct analysis of fluid inclusions within garnet using laser ablation inductively coupled mass spectrometry could provide a further test of this hypothesis.

In contrast to prior studies in which thermal effects dominate, this work provides evidence that variations in the composition of intergranular fluids can be important determinants of the scales of chemical equilibrium during metamorphism. The patchy zoning patterns observed in garnet from Harpswell Neck are caused by fluids of unusual composition: these fluids yield low solubility and thus slow intergranular diffusion for Mn, Fe, and Mg, but high solubility and thus rapid intergranular diffusion for Ca and Y.

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ESTIMATING THE SEDIMENT BUDGET FOR THE BARTON SPRINGS SEGMENT OF THE EDWARDS AQUIFER

Amy Elizabeth Hobbs, M.S. Geo. Sci.

The University of Texas at Austin, 2003

Supervisor: John M. Sharp

238 pages, 55 references

Increasing urbanization on the Barton Springs segment of the Edwards aquifer is causing concern for the survival of the Barton Springs Salamander. Construction and urbanization generate higher soil erosion rates and the increased mobile sediment may enter the aquifer causing elevated turbidity and hydrophobic contaminants. Therefore, estimating the amount of sediment entering the Edwards aquifer is necessary to evaluate the current aquifer sediment loading.

To estimate the sediment budget for the Edwards aquifer, sediment load input is estimated from suspended sediment concentrations (SSC) in the six watersheds recharging the Barton Springs segment of Edwards aquifer, and sediment load output is computed from Barton Springs turbidity and spring discharge measurements. Due to equipment and time constraints, only one watershed was monitored for SSC. Bear Creek, a rural watershed crossing the Edwards recharge zone, is sampled for SSC using two ISCO automated samplers installed next to stream discharge gaging stations. During the June-July 2002 storm event, suspended sediment samples are extracted at 1 hour to 1.5 hour intervals for the first part of the storm. The storm hydrograph for the June-July 2002 storm event has four distinct discharge peaks, but the second discharge peak damaged both automated samplers and the downstream stream gage. Thus, suspended sediment concentration data was only collected from the automated samplers for the 1st hydrograph peak.

The SSC for the other three storm hydrograph peaks is estimated using least square regression to relate stream discharge to SSC. Because the downstream gage was damaged during the flood, least squares regression is only calculated for the upstream ISCO sampling site # 2 stream discharge time series. To compute the aquifer input sediment load, the suspended sediment concentration time series was multiplied by the Bear Creek recharge rate. Based on U.S. Geological Survey stream loss studies, Barton Springs discharge records, and other Edwards aquifer discharging springs, Bear Creek contributes 13% of the total recharge to Barton Springs. To find the total sediment load entering the Barton Springs segment of the Edwards aquifer. Bear Creek's sediment load aquifer input was divided by 0.13.

To compare the aquifer's sediment load input to the sediment load output, the sediment load at Barton Spring is calculated. Turbidity measured from a probe in the main spring cave orifice is correlated to suspended sediment concentration to estimate the sediment load discharging from the springs. For the total storm period from June 29, 2002 to July 4, 2002, over 550,000 kilograms of sediment entered the Edwards aquifer and only 10,751 kilograms of sediment was discharged at Barton Springs.

A one-year sediment budget from August 1, 2001 to July 31, 2002 is also computed to examine sediment fluxes over a longer period of time. Historic U.S. Geological Survey suspended solid data collected from five of the study area six watersheds are related to stream discharge. The sediment load is calculated for each watershed based on USGS average daily stream discharge data. Barton Springs sediment output is estimated from average daily turbidity records and spring discharge. For the 8/1/01 to 7/31/02 time frame, the aquifer input is 4,511,619 kilograms and the aquifer output is 65,055 kilograms. Based on computations for the June-July 2002 storm event sediment budget and for the one-year sediment budget (8/1/01-7/31/02), there is a positive net storage of sediment in the Edwards aquifer.

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MCMC ALGORITHM, INTEGRATED 4D SEISMIC RESERVOIR CHARACTERIZATION AND UNCERTAINTY ANALYSIS IN A BAYESIAN FRAMEWORK

Tiancong Hong, Ph.D.

The University of Texas at Austin, 2008

Supervisor: Mrinal K. Sen

191 pages, 139 references, 6 tables

One of the important goals in petroleum exploration and production is to make quantitative estimates of a reservoir’s properties from all available but indirectly related surface data, which constitutes an inverse problem. Due to the inherent non-uniqueness of most inverse procedures, a deterministic solution may be impossible, and it makes more sense to formulate the inverse problem in a statistical Bayesian framework and to fully solve it by constructing the Posterior Probability Density (PPD) function using Markov Chain Monte Carlo (MCMC) algorithms. The derived PPD is the complete solution of an inverse problem and describes all the consistent models for the given data. Therefore, the estimated PPD not only leads to the most likely model or solution but also provides a theoretically correct way to quantify corresponding uncertainty. However, for many realistic applications, MCMC can be computationally expensive due to the strong nonlinearity and high dimensionality of the problem. In this research, to address the fundamental issues of efficiency and accuracy in parameter estimation and uncertainty quantification, I have incorporated some new developments and designed a new multi-scale MCMC algorithm. The new algorithm is justified using an analytical example, and its performance is evaluated using a nonlinear pre-stack seismic waveform inversion application. I also find that the new technique of multi-scaling is particularly attractive in addressing model parameterization issues especially for the seismic waveform inversion.

To derive an accurate reservoir model and therefore to obtain a reliable reservoir performance prediction with as little uncertainty as possible, I propose a workflow to integrate 4D seismic and well production data in a Bayesian framework. This challenging 4D seismic history matching problem is solved using the new multi-scale MCMC algorithm for reasonably accurate reservoir characterization and uncertainty analysis within an acceptable time period. To take advantage of the benefits from both the fine scale and the coarse scale, a 3D reservoir model is parameterized into two different scales. It is demonstrated that the coarse-scale model works like a regularization operator to make the derived fine-scale reservoir model smooth and more realistic. The derived best-fitting static petrophysical model is further used to image the evolution of a reservoir’s dynamic features such as pore pressure and fluid saturation, which provide a direct indication of the internal dynamic fluid flow.

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FAULT TIMING IN THE SIERRA MADRE ORIENTAL, NORTHEASTERN MEXICO

John Noel Hooker, M. S. Geo. Sci.

The University of Texas at Austin, August 2004

Supervisor: Randall Marrett

169 pages, 149 references, 2 tables

Two hypotheses are proposed for the timing of outcrop-scale faults in and near the Cupido Formation, a limestone-dolostone formation in the Sierra Madre Oriental in northeastern Mexico. One is syn-depositional (early Cretaceous); faults developing at this time may be the result of down-slope gravitational sliding. The other is during the Laramide orogeny (Paleogene); faults may have developed as accessory structures during fold-dominated crustal shortening. Several lines of evidence favor the former hypothesis for a significant fraction of the faults. These include physical characteristics such as growth strata and crosscutting relationships with burial stylolites, as well as associated non-brittle strain, in magnitudes beyond what is expected for lithified material under upper crustal conditions. The faults studied show complicated kinematics but are generally consistent with down-slope motion, in a radial pattern away from the early Cretaceous paleo-topographic high. The faults appear concentrated within the lowstand depositional systems of the Cupido Formation, suggesting a sedimentary control on fault initiation and propagation. Other faults crosscut early features and appear to be associated with Paleogene fold formation.

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STOCHASTIC TOMOGRAPHY AND GAUSSIAN BEAM DEPTH MIGRATION

Chaoshun Hu, PhD.

The University of Texas at Austin, 2008

Supervisors: Paul L. Stoffa and Kirk McIntosh

Ocean-bottom seismometers (OBS) allow wider angle recording and therefore, they have the potential to significantly enhance imaging of deep subsurface structures. Currently, conventional OBS data analysis still uses first arrival traveltime tomography and pre-stack Kirchhoff depth migration method. However, using first arrival traveltimes to build a velocity model has its limitations. In the Taiwan region, subduction and collision cause very complex subsurface structures and generate extensive basalt-like anomalies. Since the velocity beneath basalt-like anomalies is lower than that of high velocity anomalies, no first-arrival refractions for the target areas occur. Thus, conventional traveltime tomography is not accurate and amplitude constrained traveltime tomography can be dangerous. Here, a new first-arrival stochastic tomography method for automatic background velocity estimation is proposed. Our method uses the local beam semblance of each common-shot or common-receiver gathers instead of first-arrival picking. Both the ray parameter and traveltime information are utilized. The use of Very Fast Simulated Annealing (VFSA) method also allows for easier implementation of the uncertainty analysis. Synthetic and real data benchmark tests demonstrate that this new method is robust, efficient, and accurate.

In addition, migrated images of low-fold data or data with limited observation geometry like OBS are often corrupted by migration aliasing. Incorporation of prestack instantaneous-slowness information into the imaging condition can significantly reduce migration artifacts and noise and improve the image quality in areas of poor illumination. Here I combine slowness information with Gaussian beam depth migration and implement a new slowness driven Gaussian beam prestack depth migration. The prestack instantaneous slowness information, denoted by ray parameter gathers p(x,t), is extracted from the original OBS or shot gathers using local slant stacking and subsequent local-semblance analysis. In migration, we propagate both the seismic energy and the principal instantaneous slowness information backward. At a specific image location, the beam summation is localized in the resolution-dependent Fresnel zone where the instantaneous-slowness-information-related weights are used to control the beams. The effectiveness of the new method is illustrated using two synthetic data examples: a simple model and a more realistic complicated sub-basalt model.

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FLOW DYNAMICS OF THE PITCHSTONE PLATEAU OBSIDIAN FLOW IN YELLOWSTONE NATIONAL PARK, WY

Casey Huff, B.S.

The University of Texas at Austin, 2008

Supervisor: James Gardner

Extremely large volume rhyolite flows are known to exist, but have never been witnessed, and so little is known about how such massive, high viscosity lava flows erupt. To better elucidate their behavior, this project focused on the 70 km3 Pitchstone Plateau obsidian flow, erupted 72 ka from the Yellowstone caldera. Estimates of viscosity were combined with 3D size and number data to investigate the kinetics of groundmass crystallization and estimate flow dynamics of the using a suite of samples collected relatively evenly from near vent to the flow front. To constrain viscosity and kinetics of groundmass crystallization of the magma, we investigated the pre-eruptive storage conditions of the magma. The temperature was between 700-740°C in the chamber, and volatiles dissolved in glass inclusions contain up to 3.5 wt. % water. Groundmass glass water contents of ~0.13 wt. % water show that the melt degassed completely, which led to an increase in viscosity from <107 Pa s in the chamber to 1011.6-1012.2 Pa s during extrusion. Both the vol. % crystallinity and total microlite volumes per volume (Vtotal microlites / Vsample ) show two increasing trends within the flow. The minimum amount of crystallization within the flow was 0.16 % at the vent and the maximum was 3.37 % crystallization at the end of the flow. Crystal size distributions of pyroxene microlites showed two trends of coarsening with distance from the vent. For each trend the mode was between 2-4 µm closer to the vent, and decreased to between 0-2 µm distal the vent. Feldspar morphology also changed with distance from the vent. Closer to the vent, feldspars showed more tabular, equant shapes whereas at the end of the vent feldspars were non-tabular. The microlite patterns led us to conclude that microlite growth and nucleation are controlled by magma ascent rate in the conduit, and that these two trends probably represent two pulses of ascent within the conduit.

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FACIES ARCHITECTURE OF THE MANZANILLA FORMATION, TRINIDAD AND TOBAGO, WI

Georgia Vernelle Huggins, MA

The University of Texas at Austin, 2007

Supervisor: Ron Steel

81 pages, 43 references, 1 table

In studying the Late Miocene-Early Pliocene Manzanilla Formation of Trinidad the interaction between tectonics and sedimentation was examined using the depositional facies and sandbody architectures (processes and sub-environments) during a crucial time in Trinidad’s geological history. The formation records the interaction between the southwards thrusting of the Caribbean Plate onto northern Trinidad and the sediment influx of the paleo–Orinoco delta system from the southwest.

The Manzanilla Formation was deposited in the northern of two basins on the island. This 1,500m thick succession consists of the San Jose Calcareous Siltstone, the Montserrat Glauconitic Sandstone and the Telemaque Sandstone members, which were deposited in a tidally influenced basin. This contrasts the time equivalent south Trinidad sub-delta systems of the Columbus Basin, which suffered open ocean swell and the dominance of waves.

The dispersal patterns of the sub-delta deposits of the Manzanilla Formation, the role of syn-sedimentary tectonics in the growth of its deltas, the delta regime, architecture and the reservoir properties of the sandstones of the Manzanilla Formation was studied.

Preliminary results suggest: (1) the Manzanilla sub-delta deposits were dispersed from the paleo- Orinoco delta in the west-southwest, into a relatively protected (Central and Northern Range uplifts) Northern Basin, (2) the distal deltaic deposits were interbedded with coarser –grained material from fans of the tectonically active Northern Range, (3) the Northern Basin was tectonically stable during the L. Miocene – E. Pliocene, and (4) the Central Range had a smaller uplift at this time, which created southerly ‘protection’ for the delta system and caused the Manzanilla deltas to be tidally dominated. (5) The tidal nature of this reservoir is the key to understanding hydrocarbon distribution.

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BIOFUEL CLEAN DEVELOPMENT MECHANISM (CDM): A FINANCIAL FERTILIZER TO EXPAND BIOFUEL MARKET

In-Chul Hwang, MA

The University of Texas at Austin, 2008

Supervisor: Charles G. Groat

120 pages, 84 references, 11 table

Over recent years, world biofuel market has been rapidly expanding with strong governmental support such as biofuel mandates and tax incentives. Among many driving forces, agricultural interest has been a dominant driver behind current biofuel boom. But at the same time, it can constrain the further growth of burgeoning biofuel industry. Steep rise in food demand caused by population growth and improving standard of life will constrain growth potential of biofuel since it competes with biofuel for existing cropland and pastureland. Second-generation biofuel such as cellulosic ethanol or algae can provide a fundamental solution to various problems of current first-generation biofuel.

This thesis seeks to identify the world biofuel market potential and constraints on world biofuel market expansion and explores possible solutions to the constraints. Especially this thesis focuses on the applicability of Clean Development Mechanism (CDM) to biofuel projects as a solution to reduce financial burden of second-generation biofuel projects and thus contribute to expanding biofuel market.

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PALEOGENE TO RECENT TECTONIC AND PALEOGEOGRAPHIC EVOLUTION OF THE CARIACO BASIN, VENEZUELA

Martha Alexandra Jaimes Carvajal, M.S.

University of Texas at Austin, 2003

Supervisors: William Fisher and Paul Mann

94 pages, 64 references, 16 plates

The Cariaco basin region, located offshore of north-central Venezuela, includes the Ensenada de Barcelona shelf, the Tortuga-Margarita platform and the Cariaco basin, the largest and deepest fault-bounded late Neogene basin within the South American-Caribbean right-lateral strike-slip plate boundary. Four active fault systems are recognized in the Cariaco basin region: 1) east-west striking San Sebastian-el Pilar right-lateral strike-slip fault system, expressed as a narrow sea floor valley overlying a negative flower structure that diagonally crosses the Cariaco basin; 2) east-west striking Tortuga-Margarita fault system that exhibits mainly down-to-basin, oblique-slip throw; 3) east-west striking Ensenada de Barcelona normal-fault system,, which displays a preferential downthrown to the south; and 4) northwest-striking, right-lateral Urica fault zone, located on the Ensenada de Barcelona shelf. The Urica fault is a lateral ramp fault that forms the western edge of thrusts and folds of the Serrania del Interior fold-thrust belt.

Cenozoic convergence between the Caribbean arc and the South American passive margin was highly oblique, and diachronous with migration from west to east during Eocene to Recent time. Oblique convergence in the Cariaco basin began in the Early Miocene and continued migrating eastward along major right-lateral, strike- slip fault systems. Five tectonosequences record the interplay of tectonic and sedimentation in the Cariaco basin: 1) a ~ 0.6 km-thick Paleogene tectonosequence formed when a Cretaceous-Caribbean volcanic arc rifted to form the Tortuga and Margarita basins; 2) a ~1.65 km-thick Lower Miocene tectonosequence was controlled by a fold-thrust belt developed in the Ensenada de Barcelona shelf; 3) a 1.2 km-thick Middle-Upper Miocene tectonosequence formed by a period of extension associated with tectonic loading and thrusting in the south; and a major basin, the Cariaco pull-apart basin initiated because of misalignment between the east-west striking, right-lateral San Sebastian and El Pilar strike-slip faults; 4) a ~0.6 km-thick Pliocene tectonosequence was controlled by a period of transtension, along the San Sebastian-El Pilar right-lateral fault system; the Ensenada de Barcelona shelf subsided to form a deep basin bounded by a horst structure in the north and was filled by northward-progradational delta complexes; 5) a 1.8 km-thick Pleistocene to Recent tectonosequence formed during growth and expansion of the rhomboidally-shaped Cariaco pull-apart basin; the large expansion of the basin is attributed to mass wasting and continued filling by south-sourced progradational delta complexes.

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NEW PERSPECTIVES ON PLEISTOCENE BIOCHRONOLOGY AND BIOTIC CHANGE IN THE EAST-CENTRAL GREAT BASIN: AN EXAMINATION OF THE VERTEBRATE FAUNA FROM CATHEDRAL CAVE, NEVADA

Christopher Nathan Jass, Ph.D.

The University of Texas at Austin , 2007

 

Supervisor: Christopher J. Bell

The interaction between climate, environments, and mammalian faunas during the late Pleistocene-Holocene has been studied intently over the last several decades. Cave deposits play an important role in our understanding of these complex interactions, but they are especially significant for our understanding of the faunal history of the Great Basin . In order to develop a deeper time perspective on mammalian faunal change, I began a project that integrated several elements necessary for identifying and interpreting biotic change in the Great Basin of the western United States . These elements included development of a framework for understanding the importance of cave deposits for the paleontological record, collection of a mammalian fauna that pre-dates the terminal Pleistocene, identification of that fauna in the midst of shifting taxonomic paradigms, and evaluation of the fauna in the context of previous regional biogeographic models.

I utilized data from the FAUNMAP database to evaluate the significance of the contribution that cave deposits make to the Pleistocene mammal record. Caves do provide unique faunal data in addition to contributing a high percentage of the individual species records for late Pleistocene mammals.

Fieldwork was conducted at Cathedral Cave , NV , in order to assess a fauna that was thought to predate the late Pleistocene-Holocene transition. In excess of 30,000 identifiable fossils were recovered in an excavation area that was roughly 1.5 x 2 x 0.7 m. Prior to fieldwork in 2003, age estimates for the fauna were between 750 ka to 850 ka. New chronologic analyses suggest a more recent age ( = 146.02±2.584 ka to 151.2±4.4 ka) that extends the known chronologic distributions of several taxa and alters previously established biochronologic frameworks for the Pleistocene. This work also calls into question previous age assignments for portions of Smith Creek Cave .

Individual faunal identifications were made using a conservative data-reliant approach in order to minimize geographic assumptions and render an independent data set useful for broad biogeographic analyses. Although the faunal data presented here do not explicitly support or refute regional biogeographic models, they do indicate that patterns of faunal change can be found even when species-level identification are not achieved.


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RESIDUAL MIGRATION VELOCITY ANALYSIS IN THE PLANE WAVE DOMAIN: THEORY AND APPLICATIONS

Junru Jiao, PhD

The University of Texas at Austin, 2001

Supervisor: Paul L. Stoffa

This dissertation addresses velocity depth model building using residual migration velocity analysis in the plane wave domain. The criterion used for residual migration velocity analysis is that the results of migration with the correct velocity-depth model should reveal the same geologic structure on common image gathers (CIG's). That is, the events on the CIG are horizontally aligned since they represent the image of the same subsurface position obtained at different angles. Use of an incorrect velocity-depth model in migration causes misalignment of events in a CIG, i.e., the events on the CIG exhibit residuals. By analyzing the residuals on the CIG, we can derive the depth and the velocity corrections and thus obtain a corrected velocity depth model.

I first discuss the kinematics of seismic wave propagation and explore pre-stack depth migration in the plane wave (t, p) domain. Then, I derive the exact one, two-, and three-dimensional residual migration equations in the depth-p domain after pre-stack depth migration. To perform interval velocity analysis, a suite of velocity corrections is tested to do residual migration but only one gives the best image. The combination of this velocity correction and the original migration velocity improves the velocity model. The two main advantages of the new method are that it derives interval velocities directly and is computationally very efficient because only a top down residual migration is needed instead of top-down pre-stack depth migration. Next, I apply the new method to both the synthetic and real seismic data. The synthetic data examples show that the 2D method gives a better residual migration result than the 1D method when strong dips are present but the 1D equation also works well for 2D models when the dip angles are small. After getting a new velocity depth model, one can use the new model to perform a complete residual migration which gives much better CIG's and stacked sections than those without residual migration. Alternatively, we can also use the new model to migrate the data again and then repeat the residual velocity analysis for another iteration. The number of iterations depends on the initial model and the precision required. In the field data example, a reasonable model was obtained after only four iterations.

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MONETIZATION OF STRANDED NATURAL GAS IN THE UNITED STATES UNCONVENTIONAL RESOURCE PLAYS: DEVELOPING A GREEN INITIATIVE IN THE FORT WORTH BASIN BARNETT SHALE

Andrew Stephen Johnson, M.A.

The University of Texas at Austin, 2008

Supervisor: Charles C. Groat

World natural gas reserves are abundant, estimated at approximately 6,400 trillion cubic feet (Tcf) at the end of 2006. Much of this global supply of natural gas is considered stranded due to its location that is distant from consuming markets. The biggest challenge for exploration and production companies is to determine an economically feasible way to monetize this gas. These companies must determine whether it is economic to build a pipeline, or whether liquefied natural gas (LNG) is the best way to bring this gas to market. Exploration and production companies in the United States, unlike those in other countries, are in an advantageous position to monetize stranded gas through the development of unconventional resource plays.

The Barnett Shale in the Fort Worth Basin has progressed from a sub-economic unconventional resource play in the 1990s to the largest producing onshore natural gas field in the U.S. today. As production in the Barnett has crossed over the 2.6 Bcf / d threshold, drilling activity has extended beyond the Core, Tier 1, and Tier 2 counties to areas where the gas is considered stranded due to a constrained gas pipeline take-away capacity. Until the sufficient pipeline infrastructure is developed, advances in technology have enabled for implementation of small-scale LNG systems on well sites that provide a very attractive option for the monetization of stranded gas. Small-scale LNG systems are the first step towards a fundamental change to the utilization of LNG instead of diesel fuel that would not only enable exploration and production companies to optimally develop stranded gas reserve basins, but also provide invaluable economic, environmental, and social benefits in the future.

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GEOCHEMICAL EVOLUTION OF GROUNDWATER IN THE PLEISTOCENE LIMESTONE AQUIFER OF BARBADOS

Ian Christopher Jones, Ph.D.

The University of Texas at Austin, 2002

Supervisor: Jay L. Banner

This investigation is a comprehensive study of the hydrology and hydrogeochemistry of the Pleistocene limestone aquifer of Barbados, a tropical karst island aquifer. The purpose of this research is to investigate how groundwater compositions in a tropical karst aquifer vary spatially and temporally, and determine the factors or processes responsible for these variations. These questions are addressed by evaluating spatial and temporal variation of groundwater major and trace element and isotopic compositions, and thus determining relationships between groundwater composition variations and various hydrologic and geochemical factors. These factors include: recharge processes, groundwater flow paths, soil compositions, aquifer and aquitard rock compositions, and anthropogenic inputs. This research provides insight into natural processes that influence groundwater compositions, allowing us to: (1) better understand geochemical processes taking place in an aquifer; (2) use groundwater constituents as tracers to determine seasonal and interannual variation of recharge and to estimate recharge amounts; and (3) establish relative importance of land use and recharge processes in the susceptibility of a karst aquifer to contamination.

Key results of this study include: (1) development of a method of determining the spatial and seasonal distribution of recharge, and determine interannual variations of recharge using oxygen isotopes; (2) determination that recharge has a greater influence on susceptibility of a karst aquifer to contamination than land use; and (3) spatial ad temporal variations of groundwater major and trace element and isotopic compositions reflect and respond independently to diverse processes, for example, seawater mixing and variations of the aquifer and aquitard rock compositions encountered along flow paths.

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PROTEROZOIC TECTONIC EVOLUTION OF SOUTHERN LAURENTIA: NEW CONSTRAINTS FROM FIELD STUDIES AND GEOCHRONOLOGY IN SOUTHERN COLORADO AND NORTHERN NEW MEXICO, U.S.A.

James V. Jones III, Ph.D.

The University of Texas at Austin, 2005

Supervisor: James N. Connelly

New field studies and geochronology from southern Colorado and northern New Mexico constrain the Proterozoic growth and modification of southern Laurentia. The Sangre de Cristo Mountains of southern Colorado preserve evidence for three episodes of Proterozoic magmatism, deformation, and metamorphism. Early deformation produced penetrative, NW-striking fabrics and occurred in an arc setting between 1750 – 1730 Ma. Post-Yavapai granitoid magmatism occurred at 1695 ±2 Ma and 1682 ±3 Ma and was contemporaneous with regional quartzite deposition. Deformation at 1637 ±6 Ma produced localized NE-striking, subvertical fabrics with dextral shear sense. Granitic magmatism at 1434 ±2 Ma and 1407 ±6 Ma was accompanied by NW – SE shortening between 1420 – 1412 Ma that produced subvertical, NE-striking fabrics.

Thick sequences of quartz arenite were deposited across the region between the Yavapai and Mazatzal orogenies (ca. 1.70 Ga and 1.65 Ga). New geochronology reveals that deposition occurred on exhumed, Yavapai-aged basement (1706 ±5 Ma and 1698 ±4 Ma) with detritus dominated by Paleoproterozoic sources only slightly older than the quartzites themselves. Regional quartzite sedimentation was contemporaneous with nearly continuous magmatism in the region at deeper crustal levels. The first-cycle, syn-orogenic character of quartzites contrasts with their extreme compositional maturity, requiring perhaps anomalous environmental influences that enhanced chemical weathering during deposition.

New geochronology and structural studies from the Wet Mountains, Colorado, reveal contrasting structural styles during widespread Mesoproterozoic A-type granitic magmatism. At shallower crustal levels, strongly localized deformation at 1430+5/-3 Ma produced subvertical fabrics throughout the N-striking Five Points shear zone. At deeper crustal levels, penetrative deformation accompanying granitic magmatism at 1435 ±5 Ma and 1390 ±10 Ma produced moderately- to shallowly-dipping fabrics. Regionally consistent fabric orientations and kinematics are interpreted to represent an intracontinental response to convergent tectonism, and contrasting, yet coeval, styles of deformation require a structural discontinuity in the middle crust between ca. 1430 – 1360 Ma. Weak, flowing lower crust is consistent with models for intraplate orogenesis and the development of orogenic plateaus, and the southern Wet Mountains might represent an exhumed analog for mid-crustal, low-viscosity layers inferred beneath modern intracontinental orogenic systems such as Tibet and the Altiplano.


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ASSESSING CONTROLS OF CLIMATE, VEGETATION, AND SOILS ON DIFFUSE GROUNDWATER RECHARGE USING UNSATURATED FLOW MODELING

Kelley Elaine Keese, MSGeoSci

The University of Texas at Austin, 2005

Supervisor: Bridget R. Scanlon

Understanding climate, vegetation, and soil controls on recharge is essential for estimating potential impacts of climate variability and land use/land cover change on recharge. Recharge controls were evaluated by simulating drainage in 5-m-thick profiles using a 1-D unsaturated flow code (UNSAT-H), climate data, and vegetation and soil coverages from online sources. Soil hydraulic properties were estimated from STATSGO/SSURGO soils data using pedotransfer functions. Vegetation parameters were obtained from the literature. Long-term (1961–1990) simulations were conducted for 13 county-scale regions representing arid to humid climates and different vegetation and soil types, using data for Texas, U.S.A. Areally averaged recharge rates are most appropriate for water resources; therefore, Geographic Information Systems were used to determine spatial weighting of recharge results from 1-D models for the combination of vegetation and soils in each region. Simulated 30-yr mean annual recharge in bare sand is high (51–709 mm/yr) and represents 23 to 60% (arid–humid) of mean annual precipitation (MAP). Adding vegetation reduced recharge by factors of 2 to 30 (humid–arid) and soil textural variability reduced recharge by factors of 2 to 11 relative to recharge in bare sand. Vegetation and soil textural variability both resulted in a large range of recharge rates within each region; however, spatially weighted, long-term recharge rates were much less variable and were positively correlated with MAP (r 2=0.85, vegetated sand; r 2=0.62, variably textured soils). The most realistic simulations included vegetation and variably textured soils, which resulted in recharge rates from 0.2 to 118 mm/yr (0.1-10% of MAP). Mean annual precipitation explains 80% of the variation in recharge and can be used to map recharge.


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HYDROGEOLOGIC SIGNIFICANCE OF DEPOSITIONAL SYSTEMS ON GROUNDWATER QUALITY AND WATER RESOURCES IN THE CISCO GROUP, UPPER PENNSYLVANIAN AND LOWER PERMIAN FACIES, ROLLING PLAINS, TEXAS

Katherine S. Kier, M.S. Geo. Sci.

The University of Texas at Austin, 2004

Supervisor: Alan R. Dutton

121 pages, 54 references

Sixteen alternating carbonate and terrigenous depositional systems compose the Cisco Group (Upper Pennsylvanian, Lower Permain), part of the Eastern Shelf of the Midland Basin, of North-Central Texas. This study examines the role that the complex hydrogeology of the Cisco Group plays in determining the large heterogeneity in groundwater quality and resources across much of the Texas Rolling Plains.

A recognized problem in the area is the natural pollution of groundwater and surface water from salt springs and seeps from the Upper Pennsylvanian and Lower Permian. Whereas formational dip is west, toward the Midland Basin, the prevalent direction of groundwater flow is east, following the regional slope of the southern Great Plains. Discharge of brine from the Midland Basin and from salt-dissolution zones affects salinity in shallow aquifers and rivers across the Rolling Plains.

This project integrates geologic, hydrochemical, and hydrologic data in cross sections and plan view, and uses PHREEQC for geochemical analysis. Cross sections of the Cisco stratigraphy resolve vertical and lateral heterogeneity and indicate a strong hydrostratigraphic control on groundwater quality. A total of 654 water quality samples from Cisco formational units were extracted from the Texas Water Development Board (TWDB) groundwater database. TDS concentrations are less than 3000 mg/l in 93 percent of these samples. Sixteen Cisco saline water samples from the USGS produced water database are used in PHREEQC as an end member for geochemical mixing modeling. Mixing models confirm the influence and interaction of deep saline brines with freshwater end members in small quantities (~ ≥5 percent). Water quality is found to be controlled by: (1) mixing of locally recharged freshwater and saltwater moving eastward from the Eastern Basin and (2) reacting recharge water with formation minerals (mainly silicates and carbonates).

Although groundwater demands for all or parts of the six county study area are not expected to exceed supply needs, water demands for the neighboring Dallas-Fort Worth Metroplex are projected to increase up to 40 percent over the next fifty years. In order to provide for Texas’ growing population, options such as desalination are feasible for this study area in order to maximize the yield of groundwater supplies and should be incorporated into regional water plans.

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THRUST KINEMATICS IN THE LOWER CONGO BASIN, DEEPWATER SOUTHERN GABON

Richard E. Kilby, M.S. Geo. Sci.

The University of Texas at Austin, 2005

Co-supervisorss: Martin P. A. Jackson and Mark Cloos

Fold-and-thrust belts detach on Aptian salt along the toe of much of the Atlantic passive margin off West Africa. However, little is known about the timing and kinematics of this gravity driven shortening. For this study these topics have been investigated using a 3D seismic volume in the Anton Marin and Astrid Marin lease blocks of the Lower Congo Basin. A 27 km long by 14 km wide study area straddles the transition between updip extension and downdip thrusting. Distal structures comprise thrust faults regularly spaced at 3-4 km. Their strong seaward vergence is attributed to decoupling over thin salt. The salt became thinned by expulsion into passive diapirs before thrusting began. Thrust kinematics are analyzed using regional structural restoration, physical models and a new adaptation of a graphical technique originally designed for normal growth faults.

Thrust kinematics and salt tectonics are recorded by thickness variations in synkinematic sediments. These variations were quantified by measuring time-thickness differences in nine stratigraphic intervals along 64 traverses across six thrust faults. Fault activity indices (time-thickness ratios across thrust faults) identify the timing and intensity of slip for a specific fault. Comparison of fault activity indices both along strike and between different faults indicates that thrusting initiated in the distal part of the study area in the Albian and migrated landward in a break-back sequence. Distal thrusting ended when proximal thrusting culminated in the Late Cretaceous or early Paleogene. Structural restoration of a regional seismic line shows similar timing and corroborates the break-back thrust sequence.

While break-back thrust sequences appear to be commonly recognized, few detailed investigations exist of the phenomena, apart from the present study. Results of scaled physical experiments recreate a similar break-back sequence to those observed in seismic profiles and documented with the fault activity index and structural restoration. During shortening, distal structures tightened, and the underlying salt layer thinned as salt was fed into diapirs. Thinning of salt restricted salt flow and increased local basal resistance. At the same time, buttressing downdip became increasingly effective as the distal thrust belt thickened. The break-back sequence formed as younger thrusts initiated updip from the distal buttress.

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THERMAL, CHEMICAL AND STRAIN ANALYSIS OF A GRANITIC TECTONITE FROM THE WESTERN SALINIAN BLOCK, MONTEREY COUNTY, CALIFORNIA

Brian D. Knight, M.S. Geo. Sci.

The University of Texas at Austin, 2001

Supervisor: Mark Cloos

A 30-40 meter-wide zone of mylonitic quartz diorite was discovered in the Santa Lucia Range in seacliffs along the Pacific Ocean. When studied together with adjacent garnetiferous quartz-plagioclase veins, a detailed thermal, chemical, and tectonic history was developed for western Santa Lucia Range that has implications for the correlations between the Salinian block and the Sierra Nevada.

Petrographic analysis of the mylonite reveals that quartz deformed by crystal-plastic processes, while plagioclase occurs as cracked grains. Hornblende and biotite within the undeformed pluton are altered to chlorite and epidote in the shear zone. These microstructures and mineral assemblages are consistent with deformation under middle greenschist-facies conditions (300-450 °C). Rf/ff strain analysis, used to examine the strain geometry of deformed quartz grains in eight mylonitic samples, indicates the strain fabric ellipsoids have aspect ratios between 1.3 and 2.8. Whole-rock and trace element geochemical analyses for seven mylonitic and three undeformed samples were also obtained in order to study chemical changes that occurred during mylonitization. Calculation of systematic changes in the gain or loss of elements was done by normalizing concentration data to Al2O3, which was selected as a reference frame due to its low solubility in most metamorphic environments. Element mobility data reveal that the mylonites experienced bulk volume gains of 7 to 21% that were accommodated by major gains in SiO2 and K2O and minor losses in CaO and MgO relative to the protolith. These chemical changes are consistent with growth of quartz and k-feldspar in the mylonite at the expense of plagioclase, hornblende, and biotite in the protolith. The large volume gains indicate an influx and cooling of a potassic, silica-saturated fluid along the relatively permeable mylonite zone. The model proposed in this study suggests that the mylonite zone formed in the hanging wall above a major fault that juxtaposes granitic plutonic rocks above highly metamorphosed sedimentary rocks of the Sur Series.

Garnetiferous quartz-plagioclase veins, dated by the Rb-Sr method, yield an isochron age of 106 ± 11 Ma. In addition to detailed chemical and petrographic study of the veins, four garnet-biotite pairs were analyzed on the electron microprobe and Fe-Mg partitioning relationships yield temperatures between 700-800°C. This indicates that vein formation was contemporaneous with amphibolite- to granulite-facies metamorphism in the Santa Lucia Range. Vein origin is interpreted to be due to an influx of CO2-rich fluids through fractures, which locally dehydrated the wall rocks.

Existing age data was used to develop a cooling history for the region. The data suggest that mylonitization occurred between 80 and 72 Ma, contemporaneous with rapid cooling associated with the onset of low-angle subduction off the California margin. Also, two new fission-track ages of 52 Ma (zircon) and 2 Ma (apatite) indicate that the study area has a somewhat different Cenozoic cooling history than the rest of the Salinian block. This is explainable if the Palo Colorado fault, a strike-slip structure mapped within the Salinian block, has a significant component of dip-slip movement. On a larger scale, the lithotectonic evolution of the mylonite zone in the Santa Lucia Range is proposed as correlative to rocks with similar ages, cooling histories, and textures in the Tehachapi Mountains of the southernmost Sierra Nevada.

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FRACTURE ORIENTATIONS AND RELATIONSHIPS IN THE HUECO TANKS SYENITE, EL PASO COUNTY, TEXAS

Jennifer Nicolle Knowles, B.S.

The University of Texas at Austin, 2008

Orientations and relationships of fractures at Hueco Tanks, El Paso County, Texas, can provide further evidence toward relative timing of tectonic events affecting the Hueco Bolson in Trans-Pecos Texas. This study concludes that the 32.3 Ma Hueco Tanks intrusion was emplaced during the transition from residual Laramide compression to Basin and Range extension, recording stress orientations through fracture response in the rock mass. Three prominent fracture sets are evident at Hueco Tanks. The first prominent set, fracture set one, comprises continuous, large-scale fractures trending NE-SW across West, East, and East Spur Mountains. Fractures of set one are consistent with stresses resulting from weak compression that lasted until ~ 32 Ma. Field relationships suggest that fracture set one is the oldest. Fracture set two consists of continuous, shallow dipping, exfoliation sheets which are characteristic of unloading and decompression during exposure. Fractures of set two commonly terminate at fractures of set one, suggesting that these fractures are younger. Fracture set three consists of fractures localized in a linear zone on the eastern half of East Mountain and northeast East Spur. These fractures are oriented NNW and NNE and dip steeply west, constituting a dominant N-S trend. This localized set terminates at fractures of set two, and are interpreted as younger.

Observations from flow features and from fracture behavior suggest that rather than a stock, Hueco Tanks has a laccolith-like morphology, with North Mountain serving as the magma conduit, for the more sill-like masses that comprise West, East and East Spur Mountains.

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CHARACTERIZATION OF THE CUNNINGHAM SAND IN THE SOUTHEAST BRADLEY SPRINGER UNIT OF THE GOLDEN TREND: IDENTIFICATION OF A DELTAIC SYSTEM

Robert Lee Koch Jr., M. S. Geo Sci

The University of Texas at Austin, 2002

Supervisor: William L. Fisher

The Southeast Bradley Springer Unit, (SEBSU) is a mature field that was discovered in 1953 along the western margins of the Golden Trend in Oklahoma. The reservoir is the early Pennsylvanian Cunningham Sand of the Springer Group, which is comprised of six individual sand units, three upper sands and three lower sands. The trap for the SEBSU was formed by an erosional truncation at the base of the Atokan Unconformity caused by the uplift of the Nemaha Ridge to the east. The truncated sand was then onlapped by the Deese Group creating a seal.

The level of knowledge of the geology of the SEBSU during development in the 1950's is not known but, but it can be assumed that the interpretations are based on a theoretical framework of that time. This led to a simple layer-cake reservoir model that is inconsistent with the reservoir architecture. Presently the unit is under tertiary development and it has become apparent that the lack of geologic understanding of the reservoir architecture is the cause of numerous production problems. This project consists of defining the depositional environment and the framework of the Cunningham reservoir. The depositional framework is a controlling factor for the reservoir distribution and lateral continuity. Understanding these factors can improve the recovery from the reservoir.

The deltaic model for the reservoir was identified using a suite of data that included two cores, well logs, existing reservoir maps, and well files. The characteristics seen in the two reservoir cores were consistent with deltaic deposits. The lower three sands of the Cunningham typically exhibit a progradational log signature which is characteristic of deltaic deposits. The upper three sands have an abrupt signature characteristic of reworked deltaic deposits. Log correlations and cross sections display lateral facies changes from a fining-upward distributary channel out into delta front deposits. Isopach maps for the lower three sands display a dip orientation that coincides with the distributary channel orientation. The thickest sand, found in the northeast portions of the unit, appeared to be oriented in the down-dip direction, to the west and southwest. This emphasized the main deltaic axis created by the distributary channel prograding onto the shelf, and thinner delta front sands surround the distributary. The isopach map of the upper most sand displays a strike-oriented trend characteristic of wave reworked deltaic deposits forming a coastal or shelf sand bar.

The structural map of the base of the Cunningham, shows the western portion of the SEBSU are structurally complex. While these issues were not examined in this study, the structurally complex area contributes to reservoir discontinuity and complexity.

With knowledge of the depositional model for the Cunningham sands, an accurate reservoir model can be developed to determine and predict lateral variations in the reservoir and help solve many of the production related issues.

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EVALUATION OF DNA-LABELED CLAY PARTICLES FOR USE AS A GROUNDWATER TRACER

Daniel J. Krause, M.S. GEO. SCI.

The University of Texas at Austin, 2002

Supervisor: Philip C. Bennett

Tracing is an important hydrogeologic tool for characterizing aquifers and water resources planning. Metals, hydrophobic contaminants, particulates, and microbes are all present in aquifers as potential contaminating sources. Tracers can mimic contaminants thereby better describing their behavior in the subsurface. Labeling particles is a method that can be implemented to overcome problems common to traditional tracing methods. DNA has the potential for an ideal labeling material for several reasons, namely its extreme sensitivity to amplification. Sorption of DNA to a bentonite source clay was determined through a series of experiments involving the amplification of any unsorbed DNA in the supernatant. Remaining sorbed DNA was then physically removed from the clay surface to verify initial attachment. The DNA used in these experiments seems to suffer from extreme dilution therefore a sorption isotherm was not described. Moreover, PCR in native waters does not afford control over reaction necessary for robust product. The complexity of natural aquifer water chemistry made PCR inconsistent. These data suggest extensive methods development is necessary to achieve a field deployment of this tracer.

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LINKING THE NAGSSUGTOQIDIAN AND RINKIAN OROGENS OF WEST GREENLAND THROUGH THE DISKO BUGT REGION BY U-PB GEOCHRONOLOGY

Adam Wesley Krawiec, M.S. Geo. Sci.

The University of Texas at Austin, 2003

Supervisor: James N. Connelly

129 pages, 48 references, 1 plate

A significant portion of the North American Craton is composed of Archean age terranes that were assembled into a stable craton during the Paleoproterozoic. Recent work in the North Atlantic region of North America has shown that parallel, paired orogenic belts that were previously thought to be distinct may, instead, be related and constitute single, wide highly asymmetrical orogens. This study aims to test a correlation of the Nagssugtoqidian and Rinkian orogenies of West Greenland based on geochronological data from the Disko Bugt region.

The Paleoproterozoic Nagssugtoqidian Orogen has been extensively studied and a detailed geochronological history has been established. The tectonic history of the Rinkian Belt remains largely unresolved due to a lack of detailed mapping and geochronological framework. The Disko Bugt region lies between the well-defined Nagssugtoqidian Orogen and lesser-known Rinkian Belt. Similarities in deformation and style in the Nagssugtoqidian and Rinkian orogens suggest a genetic link exist between the two. If deformation in the Disko Bugt region can be correlated with the Nagssugtoqidian Orogen, it would imply that the Nagssugtoqidian and Rinkian orogens comprise a single >1100 km-wide asymmetrical collisional zone, similar in extent to the present day Himalayas.

Four previously recognized domains were sampled in a N-S transect across Disko Bugt and analyzed using both thermal ionisation mass s pectrometry (TIMS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Samples were selected that could provide protoliths ages and the age of deformational and metamorphic events in the region.

Results from twelve samples suggest the presence of two Archean blocks in Disko Bugt, each with a distinct age and geological history. These new ages necessitate a re-examination of the previously described domains. In addition, temporal elements of the Southern Block are coeval with the basement of the Nagssugtoqidian Orogen. Whereas the Northern Block shares a similar history with the basement of the Rinkian Belt. This evidence supports the idea that the Disko Bugt harbors a suture between two Archean terranes, a required component that has yet to be confirmed in West Greenland. Paleoproterozoic deformation across Disko Bugt is coeval with that in the Nagssugtoqidian and Rinkian orogens, thus, establishing a link between the two belts.

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TECTONICS AND SEQUENCE STRATIGRAPHY OF THE VENEZUELAN BASIN, CARIBBEAN SEA

Margaret Emily Kroehler, M.S. Geo. Sci.

The University of Texas at Austin, 2007

Supervisors: Paul Mann & Gail Christeson

The central core of the Caribbean plate is the 3-4-km-deep Venezuelan Basin that is underlain by late Cretaceous oceanic plateau and oceanic crust. The Venezuelan Basin is obliquely subducted to the east-southeast beneath the continental South American plate at the east-west-trending South Caribbean deformed belt (SCDB), a 50-100-km-wide wedge of accreted sedimentary rocks. I have mapped the structure and sequence stratigraphy of five late Cretaceous to recent sedimentary sequences overlying a 230,000 km 2 area of the Venezuelan Basin . The dataset includes ~5900 km of 2D seismic reflection data acquired during five separate surveys from 1974-2004; these seismic data are tied to DSDP drill sites 146/149 and 150 which provide age and lithologic control on the interpreted sequences. I use these data to document older Cretaceous faults formed soon after the formation of the plateau and oceanic crust; to explain the along-strike variations in structural style of the actively subducting Caribbean plate; and to constrain the age and tectonic mechanism for the initiation of subduction along the SCDB. The earliest set of faults are normal faults, only affect rocks of Late Cretaceous age, and approximately parallel a set of seafloor-spreading magnetic anomalies described by previous workers. These normal faults are widely spaced in the area of smooth-topped lava flows making up the 15-km-thick oceanic plateau, but they are much more densely distributed in the area of abnormally thin (3-5-km-thick), rough-surfaced, oceanic crust in the eastern Venezuelan Basin. The faults are interpreted as the result of back-arc extension behind the Aves volcanic arc during the late Early to Late Cretaceous. Selective reactivation of inherited faults and new bending-related faults affecting late Cretaceous to recent sedimentary sequences strike east-west and parallel the trend of the SCDB. The age of the initiation of subduction at the SCDB has been determined based on the age of onlapping, wedge-shaped, sedimentary sequences in the Venezuelan Basin . Subduction began in the western Venezuelan Basin in the middle Eocene in the western study area, in the early Miocene in the central study area, and in the post-early Miocene-Recent in the eastern study area. The ages of subduction agree with a similar eastward younging in the age of folding and thrusting in northern South America . From this observation I infer that subduction of the Caribbean plate beneath the SCDB initiated as a backthrust response to collision between the Caribbean arc and the South American continent that began in the early Eocene and youngs in an eastward direction.

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EFFECTS OF URBANIZATION ON HYDROGEOLOGICAL SYSTEMS: THE PHYSICAL EFFECTS OF UTILITY TRENCHES

Jason Noel Krothe, M.S. GeoSci

University of Texas at Austin, 2002

Supervisor: John M. Sharp, Jr.

The effects of urbanization and, specifically, the construction of utility trenches can have a profound affect on groundwater flow systems and contaminant transport. Construction of sewer, water and other utility lines can greatly disturb the natural hydraulic characteristics of surficial geologic materials. Field hydraulic conductivity (K) tests indicate that trench hydraulic conductivities ranged from one to ten orders of magnitude higher than the undisturbed soils developed at sites on the Austin Chalk, Glen Rose Limestone, and the Colorado River alluvium. Using these data MODFLOW computer models simulated the effects of higher hydraulic conductivities on groundwater flow and contaminant transport. Three different trench geometries were used for the simulations: 1) parallel to groundwater flow; 2) perpendicular to groundwater flow; and 3) a hypothetical city utility system.

The parallel and hypothetical city trench geometries resulted in several significant findings on contaminant transport in urban areas. The first finding is that contaminants flowed in directions not predicted by the direction of the regional hydraulic gradient. The second finding is that the contaminants move as much as ten TimesNewRoman faster through the utility trenches than through the undisturbed soil. These findings suggest that contaminant remediation would be more difficult and would necessitate more comprehensive fieldwork before suitable remediation plans are devised. Finally simulations, 1 and 3, suggests that lateral dispersion of the plume increased with increased hydraulic conductivity of the utility trench. This increase in lateral dispersion could result in an increase in natural attenuation. Simulation 2 also indicates that if the trench is orientated perpendicular to groundwater flow no change in plume speed or lateral dispersion occurs. The lack of change to the system in Simulation 2, and the dramatic changes seen in simulations 1 and 3, suggest that trench orientation to groundwater flow is the major factor in the alteration of groundwater flow.

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PARAMETER INVERSION FOR SEISMIC ANISOTROPY

Chandan Kumar, Ph.D.

The University of Texas at Austin , 2006

Supervisors: Robert J. Ferguson and Mrinal K. Sen

An important objective of reflection seismology is to transform a seismic dataset into a reflectivity image of the subsurface. Reflectivity imaging involves removal of propagation effects by creating an inverse propagation operator using an estimated macro velocity model. The accuracy of a reflectivity image depends on the accuracy of the velocity model used. Hence, the estimation of a good velocity model is crucial. Flat sedimentary layers, though laterally homogeneous over small-scale, often exhibit a simple kind of anisotropy called vertical transverse isotropy (VTI). Negligence of anisotropy in migration may result in significant deviation of an imaged reflector from its true position. Our ability to estimate anisotropic parameters using limited aperture, limited bandwidth seismic data is restricted. Several recent developments in data acquisition including more intense acquisition (e.g., 3-D, 4-D), broader bandwidths, and new survey methodologies (e.g., Ocean Bottom Seismics and vertical cables) have improved our ability in dealing with anisotropy. In light of these recent developments the objective of my research is three-fold - (i) finding better algorithms for anisotropy estimation that makes use of enhanced data acquisition, more powerful computers and graphical interfaces, (ii) understanding and re-evaluating our limitations/capabilities of anisotropy estimation in light of the new algorithms, and (iii) using the results of analysis as an aid to constrain anisotropy estimates.

The Common Focus Point (CFP) technology defines a recent method of prestack migration velocity analysis which has several advantages over other popular methods. One remarkable advantage is that the imaging error is given directly in time allowing easier model updates through inversion. The CFP technique has been used in recent past for estimating isotropic heterogeneous velocity model for geologically complex subsurface. For my research, I extend this method to anisotropic parameter inversion by suitably implementing the space-time domain version of CFP method for picking the traveltime error resulting from the incorrect guess model. I successfully implement this approach to estimate anisotropy of the shale thrust-sheets in the Canadian Foothills model. This model has targets of interest below transversely isotropic shale thrust-sheets and estimating anisotropic parameters is important for proper depth imaging of target zone. The synthetic P-mode data used for the analysis has been generated using a finite difference algorithm.

In order to quantitatively assess the advantages or limitations of CFP domain velocity analysis in estimating the anisotropic parameters, I have performed sensitivity analysis under different experimental settings like different observation apertures, layer thicknesses, tilt in symmetry axis, picking error and the use of mode converted data. The results quantitatively establish the advantage of joint inversion of P-P and P-Sv over the conventional inversion of solely P-P data in constraining the depth and anisotropic parameters. Also the constraint on parameter estimation improves with increase in angle of tilt of symmetry axis with respect to the reflector.

The CFP domain analysis also has advantages in dealing with mode converted P-Sv data as separate focusing at the receiver side and source side allows it to deal with one wave type at a time. In complex media, this helps avoid the cumbersome calculation of common conversion point (CCP) location. The CFP analysis has been applied for estimating anisotropic parameters as well as layer thickness by joint inversion of P-P and P-Sv synthetic data for the geology encountered in Blackfoot field.

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ANALYSIS OF MULTICOMPONENT SEISMIC DATA FROM THE HYDRATE RIDGE, OFFSHORE OREGON

Dhananjay Kumar, Ph.D.

The University of Texas at Austin, 2005

Supervisors: Mrinal K. Sen and Paul L. Stoffa

Multicomponent seismic data can be used to derive P- and S-wave velocity structures of the subsurface, which can be used further to estimate rock and reservoir properties. Most seismic analysis methods and algorithms assume that the earth is isotropic. In many geologic situations, however, sedimentary rocks exhibit anisotropic behavior, and the isotropic assumption will introduce errors in the estimates of the elastic properties of the subsurface. With the goal of analyzing multicomponent seismic data from complex regions (which may show anisotropic behavior), I have developed new algorithms for 1) seismic modeling based on a ray-Born approximation and 2) traveltime computation in tilted transversely isotropic media based on Fermat’s principle. This new traveltime computation algorithm is tested on prestack depth migration of a physical model dataset. Such algorithms are essential for estimating subsurface rock properties in complex areas such as the Hydrate Ridge area, offshore Oregon.

I participated in the acquisition of multicomponent seismic data (summer 2002), at the Hydrate Ridge of the Cascadia convergent margin. The primary goal of the experiment was to map the gas hydrates and free gas, and to understand the mechanism of fluid migration. Gas hydrate is an ice-like substance that contains low molecular weight gases (mostly methane) in a lattice of water molecules. Gas hydrates and free-gas are generally detectable with seismic methods because the seismic velocity increases in the presence of gas hydrates, and it decreases in the presence of free-gas. My analysis results in estimates of P- and S-wave interval velocities and anisotropic parameters with the final goal of relating these parameters to the presence and quantification of gas hydrate and free gas. I performed interval velocity analysis in the τ-p (intercept time - ray parameters) domain following three main steps: 1) P-wave velocity analysis, 2) P- to S-wave (converted PS-wave) event correlation, and 3) S-wave velocity analysis. P- to S-wave event correlation is done using synthetic seismograms and traveltime tables. Seismic velocities are correlated to gas hydrate and free gas saturation using a Modified Wood equation. I find that Hydrate Ridge is heterogeneous and is weakly anisotropic (maximum of 10%) in some regions caused possibly by the hydrate veins. The P-wave velocity is more sensitive to the saturation of gas hydrates (maximum of 7% of rock volume) and free gas than the S-wave velocity. The S-wave velocity does not show an anomalous increase in the hydrate-bearing sediments. Thus, I conclude that hydrate does not cement sediment grains enough to affect shear properties. It is more likely that the hydrates are formed within the pore space in this region.

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PORE PRESSURE PREDICTION USING MULTICOMPONENT PS-WAVE SEISMIC VELOCITIES: COLUMBUS BASIN, TRINIDAD W.I.

Kimberly Melissa Kumar, Geophysics MSGeoSci

The University of Texas at Austin , 2006

Supervisor: Robert J. Ferguson

I estimate overpressure in a seismic cross-section along a 12km traverse associated with a 2D/4C OBC line in the Columbus Basin , Trinidad, West Indies , where shallow gas reduces both data quality and apparent seismic velocity for P-waves, using a modified Eaton's equation for PS-waves. Pore pressure prediction using the modified Eaton's method involves velocity analysis, conversion of the stacking velocities to interval velocities via the Dix's equation, converting the interval velocity trends to pressures and mudweights, and comparison of the predictions to 3 wells surrounding the seismic line.

In the presence of shallow gas, the magnitude and areal extent of seismically derived P-wave and PS-wave velocity deviates from regional trends along the seismic line. PS-waves show a more accurate areal extent of velocity deviation due to overpressure than the P-wave, which is also affected by the presence of shallow gas. I verify my derived velocities and predicted-pressure values using sonic log data and observed pressure from 3 wells. Direct comparison between the sonic-derived velocities and the seismic-derived velocities shows that shallow gas reduces P-wave velocity, and that PS-wave velocity is less affected. Pressure prediction is verified using mudweights and formation tests from well logs and drilling reports. I find pressure predictions associated with P-waves, especially in areas of shallow gas are less reliable than for pressure predictions using PS-waves. I conclude that PS-wave velocity provides a superior map of overpressure in this region in areas with shallow gas clouds.

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PETROLOGY OF THE SOUTHWEST MARGIN OF THE GRASBERG IGNEOUS COMPLEX, PAPUA, INDONESIA

Adam L. Lambert, MS GeoSci

The University of Texas at Austin , 2008

Supervisor: Mark Cloos

398 pages, 46 references, 1 table

The 3 Ma Grasberg Igneous Complex (GIC) of Papua, Indonesia is host to a super-giant porphyry copper-gold deposit. The GIC is shallowly emplaced into folded and faulted limestones that are as young as late Miocene. The Heavy Sulfide Zone (HSZ) is a pyrite-rich shell that surrounds the GIC. The HSZ grades into the Marginal Breccia. Near the surface the Marginal Breccia is overlain by the Banded Clay, a halloysite-clay rich unit. This study has determined the relationship of these units and characterized the pervasive alteration from the petrology of 588 samples collected from five drill cores and 23 outcrop samples.

The initial Dalam phase of intrusion generated ~5 m of skarn (epidote, garnet, and clinopyroxene) at the margin of the GIC below 3700 m elevation. The precipitation of magnetite in the core of the GIC, the hydrolysis of SO2, and the precipitation of pyrite in the periphery of the deposit generated abundant HCl and H2SO4. In the outer GIC, primary igneous minerals were altered to sericite, quartz, and pyrite by the acidic hydrothermal fluids. These fluids dissolved carbonate host rock and precipitated abundant pyrite. Layered dissolution infill indicates porosity was locally very high. High permeability along the margin of the GIC would have channeled hydrothermal fluid upwards.

As supporting carbonate rock was dissolved forming the Marginal Breccia, open fractures formed along the contact with the GIC. Pyrite precipitated into these fractures, forming layering in places. Unsupported pieces of igneous rock and skarn broke off and fell into openings which became filled with pyrite. This process caused most of the growth of the HSZ to progress inward, leaving rocks that were once at the margin of the GIC separated from it by lenses of massive pyrite. Minor sphalerite and galena precipitated at lower temperatures at the outer edge of the HSZ. Only trace amounts of copper sulfides are present within the pyrite-rich HSZ because nearly all the copper was precipitated in the center of the deposit. Any H2S or SO2 remaining in the upwelling fluids mixed with oxygenated meteoric waters forming concentrated H2SO4, which intensely altered volcanic sediments forming the Banded Clay.

The dissolution-enhanced permeability along the contact zone facilitated the drainage of magmatic fluids. This acted to increase the fluid pressure gradient driving pervasive infiltration between the center and the margin of the GIC. This was a significant contributing factor to the creation of the super-giant orebody. The dissolution of carbonate wall-rock caused the GIC to collapse outwards. This caused extension fracturing within the GIC that diverted fluid flow upwards and back into igneous rock. As a result some of the outermost igneous rock in the upper part of the GIC is relatively fresh, with primary groundmass orthoclase and plagioclase phenocrysts. The outward collapse of the GIC generated the flaring-upward shape that is a distinct attribute of the Grasberg system.

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FATE AND TRANSPORT OF ARSENIC AND ANTIMONY IN THE EL TATIO GEYSER FIELD, CHILE

Jeffrey Thomas Landrum, MS Geo Sci

The University of Texas at Austin , 2007

Supervisor: Philip C. Bennett

El Tatio Geyser Field (ETGF), northern Chile , hosts widespread geothermal activity, with very high aqueous concentrations of arsenic and antimony, higher than any other known geothermal system. Boiling springs (86°C) discharge circum-neutral pH, Na-Cl type waters with low organic carbon. Net discharge of a stream draining the ETGF basin is approximately 10 cfs. As( III ), the dominant As species in discharge waters, rapidly oxidizes to As(V) at an estimated first order rate of 0.35 min -1 , determined in the field by first arrival of a tracer. As and Sb concentrations and speciation in hydrothermal waters, deposits, and microbial biomass are evaluated as a product of microbial metabolism, sorption to metal-oxyhydroxides, and co-precipitation. Mechanisms controlling these reactions ( i.e. cooling, evaporation, changes in redox and pH) are evaluated and modeled. Sequential extractions reveal that As, sorbs to Fe and Mn oxy-hydroxide complexes. In contrast, Sb solid phase partitioning is influenced primarily by the co-precipitation of Sb-oxide minerals with siliceous sinter (up to 2% wt. Sb). Diurnal variations occur in spring water chemistry and may cause Sb-rich laminations in siliceous hydrothermal deposits. Microbial energetics calculations and enrichment experiments suggest that microbial activity influences the mobility of As, and probably Sb in the ETGF basin by altering redox speciation and sorption to microbial biomass.

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AN EVALUATION OF THE PRESSURE DEPENDENCE OF RARE-EARTH-ELEMENT CONCENTRATIONS IN GARNETS FROM THE LLANO UPLIFT

by Edward David Lane, M.S.Geo.Sci.

The University of Texas at Austin, 2003

Supervisor: William D. Carlson

184 pages, 31 references, 1 CD-ROM

Application of a proposed rare-earth element (REE) geobarometer to highpressure metamorphic rocks from the Llano Uplift in central Texas yields pressures inconsistent with phase assemblages and garnet-orthopyroxene barometry. However, REE-abundance curves appear to vary systematically with pressure, suggesting that more elaborate barometers based on REE behavior may eventually be devised.

The Llano Uplift has experienced a complex metamorphic and deformational history, including an early high-pressure metamorphism and a later low-pressure heating event. The later event caused widespread resorption of the high-pressure equilibrium mineral assemblages, which greatly limits the application of quantitative geobarometers that rely on analysis of equilibrium vi assemblages. This study sought to extrapolate a new geobarometer to high pressure to increase understanding of the early metamorphic history of the Llano Uplift.

Bea et al. (1997) proposed a single-phase geobarometer based on systematic flattening of garnet REE-abundance curves with increasing pressure, using the ratio of Gd to Dy in garnet as a proxy for this effect. Their results indicate a linear correlation between this ratio and pressure for pelitic rocks in a pressure range of 0.4 to 0.9 GPa. This study tests the extrapolation of this barometer to higher pressures, using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to measure REE concentrations at interior and rim locations of centrally sectioned garnets from garnet-clinopyroxenites found at Whitt Ranch in the northern portion of the Llano Uplift and at Purdy Hill in the western portion of the Uplift, and from pelitic gneisses found at the Purdy Hill locality.

Application of the Bea et al. (1997) geobarometer to Whitt Ranch garnets yields pressures that range from approximately 0.4 to 0.5 GPa; Purdy Hill mafic garnets yield pressures of approximately 0.4 to 1.0 GPa; and Purdy Hill pelitic garnets yield pressures of approximately 0.4 to 0.5 GPa. REE-abundance curves from Whitt Ranch garnets are steeper than those from Purdy Hill mafic garnets. Whitt Ranch garnet curves show a gradual flattening effect and the disappearance of negative Eu anomalies from interiors towards rims. Purdy Hill mafic garnet vii curves show a gradual steepening from interiors towards rims and positive Eu anomalies in both interiors and rims. Purdy Hill pelitic garnet curves show initial steepening followed by flattening in heavy REE (HREE) concentrations from interiors towards rims and the presence of negative Eu anomalies in both interiors and rims.

Pressures of 0.4 to 1.0 GPa for the high-pressure metamorphism are not consistent with garnet-orthopyroxene geobarometry for the western portion of the Llano Uplift, which indicates pressures of 1.5 to 2.1 GPa (Anderson, 2001) nor with pressure estimates based on garnet-inclusion suites in Whitt Ranch rocks, which indicate a transition from upper-amphibolite- to eclogite-facies conditions. Very slow diffusion rates for REE in garnet (e.g., Van Orman et al., 2002) suggest that these inconsistencies are not diffusion effects caused by the later event, but instead represent growth zoning. However, REE-abundance curves from Purdy Hill mafic garnets are flatter than those from Whitt Ranch garnets, which suggests that flatter curves reflect higher pressures, corroborating the results of Bea et al. (1997). Flattening of curves from interiors to rims suggests that Whitt Ranch garnets grew as pressure increased, which is supported by the distribution of inclusions in garnet: interiors contain plagioclase inclusions but rims do not, which also accounts for the rimward disappearance of negative Eu anomalies. Steepening of REE-abundance curves in Purdy Hill mafic garnets may imply growth during decompression, although positive Eu-anomalies suggest viii breakdown of plagioclase during garnet growth. REE-abundance curves in pelitic garnets are more complex, and may record a change in the accessory phases present during the latter stages of garnet growth.

The ratio of Gd/Dy alone fails to capture the complex behavior of the REE over the full range of pressure commonly experienced by crustal metamorphic rocks, although the shapes of the REE-abundance curves for the Llano rocks change systematically with pressure in a manner similar to the pattern described by Bea et al. (1997).

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PHYSICAL MODELING OF NORMAL FAULTS AND GRABEN RELAYS ABOVE SALT

Joël Hervé Le Calvez, Ph.D.

The University of Texas at Austin, 2001

Supervisors: Randall Marrett and Bruno Vendeville

In salt basins, thin-skinned extension is typically accommodated by graben development in sedimentary overburden and viscous flow in the evaporitic layer. This study presents a series of physical models in which grabens propagate along strike and interact in relay zones whose geometry depends on graben across-strike separation.

I first describe the basis for physical modeling, including scaling analysis. I then review various experimental designs used by previous authors to model the interaction between laterally offset faults, finally I introduce a design in which faults nucleate at predetermined locations above small initial instabilities but that permits faults to propagate freely thereafter.

I used series of systematic experiments to investigate the 3-D geometry and evolution of two laterally offset grabens interacting in a relay zone. Results allow the determination of the influence of key geologic parameters on the evolution of relay zones. The main parameter, the across-strike offset between the grabens, controls the size (along both strike and dip) of the relay zone and its structural style. Where the offset is large, fault traces curve gently toward one another and fault throw and amount of diapir rise below the graben decrease progressively toward the relay zone. Some distance from that zone, old faults cease to slip as new faults form. In the relay zone old fault segments remain active and no new faults form. Some new faults hard-link along strike with active segments of older faults. Offset grabens and faults start interacting only when they have propagated along strike far enough to overlap. Syntectonic sedimentation can suppress new-fault formation during extension. Another experiment shows that inversion of graben relays by late shortening forms reverse faults rooted at depth on the crest of underlying diapirs.

A second series of experiments, motivated by a field example in Canyonlands National Park, focuses on the genesis of graben arrays having regionally arcuate traces. Curvature is explained in terms of shear stresses between extending domains of the sedimentary cover, which is underlain by an evaporitic décollement, and lateral nonextending domains, a setting common along salt-bearing passive margins during thin-skinned extension.

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THE CONCENTRATION OF OFFSHORE DRILLING MARKETS

Jaewon Lee M.A.

The University of Texas at Austin, 2008

Supervisor: Christopher J. Jablonowski

71 pages, 36 references, 35 tables

This paper investigates the history of mergers and acquisitions in global offshore drilling markets from 1990 to 2005. Based on this history, the effect of increasing market concentration on prices (rig rates) is examined using a regression analysis. Industry concentration is measured by The Herfindahl- Hirschman Index (HHI). Two segments of the global drilling rig market are examined: jackup and semisubmersibles. There is strong evidence to support the conclusion that increasing market concentration in the jackup drilling rig market has resulted in increased prices; the evidence is weaker for the semisubmersible drilling rig market, but there appears to be a positive impact in this sector also This result is important for industry as it tries to understand the drivers for ever- increasing exploration and development costs. This result is also important for anti-trust regulators who are charged with maintaining competitive markets. A thorough analysis and formal treatment of the time series aspects of the data sets is outside the scope of this thesis and has been reserved for future analysis.

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RADAR INTERFEROMETRY MEASUREMENT OF LAND SUBSIDENCE IN EL PASO, TEXAS

Erick Leuro, MSGeoSci

The University of Texas at Austin, 2004

Supervisor: Clark R. Wilson and Sean Buckley

119 pages, 46 references

This work presents the application of radar interferometry to detect land subsidence associated with water pumping in El Paso, Texas and adjacent areas. Geological and hydrological information are compared with the radar information to validate the results. An error treatment of the measurements is performed using the singular value decomposition technique.

Synthetic aperture radar interferometry is a proven remote sensing technique to detect ground deformation in a three-dimensional scale with millimetric precision. It has been applied successfully in earthquake monitoring, volcano deformation, glacier movement and aquifer compaction.

El Paso and Ciudad Juarez are located over the Hueco Bolson aquifer, an unconsolidated alluvial aquifer that consists of gravel, sand, silt and clay. Because of increased water pumping since the early 20 th century, the water table has changed and subsidence has occurred. Measurements of land subsidence are reported from the 1950s, 1970s, and 1980s. This work considers subsidence in the 1990s.

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STRUCTURAL ANALYSIS AND DETRITAL ZIRCON PROVENANCE IN THE WESTERN LLANO UPLIFT: IMPLICATIONS FOR A SOUTHERN COLLIDER

Jamie Sloan Fentiman Levine, MSGeoSci

The University of Texas at Austin, 2005

Supervisor: Sharon Mosher

Structural and metamorphic analysis, mapping and detrital zircon geochronology was conducted within the Mesoproterozoic Valley Spring Gneiss, in the western Llano Uplift, along an 8 km section of the Llano River west of Castell, TX. Comprising granitic gneisses and pelitic schists, with volcanic, plutonic and supracrustal protoliths, the protolith to the Valley Spring Gneiss was deposited on Laurentia and records an uppermost amphibolite facies, polyphase deformation history consistent with continent-continent collision during the Grenville orogeny.

The Valley Spring Gneiss is characterized by both ortho- and paragneisses. To determine the provenance, three paragneiss samples were analyzed using laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to establish ages for 80 zircons from each sample. All three samples show a major peak at 1200-1350 Ma and a smaller Paleoproterozoic peak. One sample had a small Archean peak. All data are consistent with a Laurentian origin for the sediment, with Mesoproterozoic sediment derived locally. Kalahari and Amazonia, which have been proposed as colliders with Laurentia, are unlikely sediment sources for rocks of the Llano Uplift.

Six phases of synmetamorphic deformation have been documented. The mineral assemblage, including K-feldspar and sillimanite, indicates conditions above the second sillimanite isograd. Evidence for supersolidus conditions throughout deformation are widespread. Three types of leucosomes, indicative of partial melting, are parallel to early foliations. Pegmatites and granitic dikes are associated with late-stage folds and ductile shear zones; they increase in abundance eastward. The earliest deformation is characterized by two generations of isoclinal folds and penetrative metamorphic foliations, S 1 and S 2, which together form the dominant, northwest-striking, northeast- dipping metamorphic layering. The third phase, F 3, is characterized by tight folds that fold the S 1/S 2 foliation with an associated axial planar foliation. The F 3 fold axes plunge moderately to the southeast; axial planes are dominantly northwest-striking. Open, late generation folds (F 4 and F 5) refold earlier structures on both outcrop and map scales. F 4 and F 5 folds are northeast-plunging with northeast- to east-striking axial planes and southeast-plunging with northwest- striking axial planes, respectively. Late boudinage and shear zones containing melt are associated with an extensional D 6 phase of deformation. Granite and pegmatite intrusions are both syn- and post-tectonic as indicated by the presence or absence of the S 1/S 2 foliation, folding and boudinage.

The sequence, style and orientation of the structures in this area correlate with those within the Packsaddle Schist and the Lost Creek Gneiss of the western Uplift. Orientations, structural stacking and definition of domain boundaries differ between the eastern and western portions of the Uplift, supporting the likelihood that deformation in the eastern Uplift was controlled by collision of the exotic arc terrane present there, whereas the western Uplift, where the island arc is absent, directly records deep-seated effects of a continent-continent collision.

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THE HYDROLOGIC FUNCTION OF SMALL SINKHOLES IN THE EDWARDS AQUIFER RECHARGE ZONE

Adrien Lewis Lindley, M.S.

The University of Texas at Austin, 2005

Supervisor: John M. Sharp, Jr.

Thin soils on Cretaceous karst bedrock typify the Edwards aquifer recharge zone in central and south Texas U.S.A. Most of the recharge occurs in major streambeds in this region, but abundant evidence of active karstic dissolution suggests that some of the recharge is occurring in the uplands. The City of San Antonio uses the karstic Edwards aquifer as its main municipal water source, and is undergoing rapid development in the uplands of the aquifer recharge zone. What is the risk to water quality of development over typical small-scale yet abundant upland karst features? This project is designed to determine more precisely what constitutes a significant recharge feature in the context of state law by directly measuring infiltration rates of typical upland karst features.

The hydrologic function of the soil and bedrock system in small sinkholes, identified by their morphological characteristics, and background areas is determined by large-scale constant head infiltration tests, microtopographic and soil thickness surveys, dye tracing and subsequent excavation of features, and imaging the subsurface with GPR.

Measurements made with a large-scale single ring infiltrometer compare typical upland karst features to paired control plots. The average infiltration per unit head for sinkholes is slightly higher than background in areas with similar soils (0.30 1/hr for sinkholes and 0.27 1/hr for background), though both are within the range for local soils. Results from infiltrometer experiments indicate the thin clay soils typical in the uplands dominates the infiltration process, yet recharge via these features under natural conditions is greater than background when ponding occurs due to their maintained microtopography. As the thin soils typical in the uplands of the Edwards aquifer recharge zone dominate the infiltration process in these small sinkholes, as shown by ring infiltrometer experiments, the risk of recharging poor quality water via these small features from developed areas sufficient to pose a threat to aquifer water quality is little greater than background.

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GEOCHEMICAL EVOLUTION OF URANIFEROUS SODA LAKES IN EASTERN MONGOLIA

Benjamin Shawn Linhoff, MSGeoSci

The University of Texas at Austin, 2008

Supervisor: Philip C. Bennett

Extremely high concentrations of U were discovered in hypersaline soda lakes in eastern Mongolia. The lakes are small, shallow (<1km2, <1m), and terminal with variable salinity. The origin and fate of U in these lakes was investigated using geochemical analyses and modeling, using samples collected from lakes and lake pore waters, wells and a stream. Samples were analyzed for Sr and U isotopes, cations, trace metals, anions, total inorganic carbon (TIC), and unstable field parameters.

A representative groundwater in the field area is dilute and alkaline, with pH=7.9, 10 mmol L-1 of TIC and 5 mmol L-1 Cl-. In contrast, a representative lake water is pH~10 with TIC and Cl- each more than 1000 mmol L-1. Uranium concentrations in lake waters range from 0.24 to more than 62.5 µmol L-1, possibly making these lakes the highest naturally occurring U concentrations ever reported in a natural water. Groundwater concentrations of U range from 0.03 and 0.43 µmol L-1.

The U is natural and derived from groundwater discharging to stable closed basin lakes. Waters are concentrated by evaporation and U(VI) is chelated by CO3-2 to form the highly soluble UO2(CO3)3-4. Two sets of well waters with corresponding lake discharge waters were analyzed for U isotopes. Unnatural concentrations of 235U were tested for, the presence of which would indicate fallout-derived U. The average of four samples was 238U/235U=136±2 indicating that the U is naturally derived. δ234U between one well and its corresponding discharge lake had similar δ234U values (δ234U=837.6-858.5). The other sample pair however, revealed significant differences between the well and its discharge lake (δ 234U=303.6-1530). This suggests nuclide recoil is significantly enriching one of the lakes with 234U beyond secular equilibrium during alpha-decay of 238U in lake sediments or along the groundwater flow path. Modeled evaporation of lakes demonstrates that a U-mineral phase is likely to precipitate during evaporation.

Strontium isotopes varied in groundwaters between 87Sr/86Sr= 0.706192-0.709776 and in lakes 87Sr/86Sr=0.708702-0.709432. Cretaceous mafic rocks likely account for low 87Sr/86Sr values while Cretaceous alkaline rhyolites account for the high 87Sr/86Sr values. High concentrations of U, Na, Cl-, and K correlate to radiogenic Sr in lake waters indicating that U is sourced from local Cretaceous alkaline rhyolites.

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THE AREQUIPA-ANTOFALLA BASEMENT, A TECTONIC TRACER IN THE RECONSTRUCTION OF RODINIA

Staci Lynn Loewy, Ph.D.

The University of Texas at Austin, 2002

Supervisor: James N. Connelly

The Arequipa-Antofalla Basement (AAB), an anomalous Proterozoic block along the central Andean margin of South America, may be critical to reconstruction of the Meso-Neoproterozoic supercontinent, Rodinia. Dalziel (1994) proposed that the AAB is an allochthonous block, transferred to Amazonia from northeastern Laurentia as a result of ca. 1.0 Ga collision between the two continents during the amalgamation of Rodinia.

New U/Pb geochronology and whole-rock isotope geochemistry from the AAB and northeastern Laurentia are used to test this proposed correlation. Based on U/Pb ages, growth polarity, sequence of age provinces, and whole-rock Pb isotopic signatures I conclude: (1) the AAB is a single basement block that formed through progressive growth within a larger continent, (2) neither Amazonia nor Laurentia were its parent craton, and (3) the AAB accreted to Amazonia during the ca. 1.0 Ga Sunsás Orogeny. Thus, the data do not support the proposed collision between Amazonia and northeastern Laurentia. Instead, the characteristics of the AAB are consistent with derivation from Kalahari. Moreover, critical examination of existing Pb data also reveals that the Pb signature of the isotopically distinct ca. 1.1 Ga basement of the southern and central Appalachians matches that of southwestern Amazonia. Based on these potential correlations, I propose an alternate position for Amazonia within Rodinia, adjacent to southeastern Laurentia and western Kalahari.

Evaluation of Pb isotopic signatures from juvenile rock units of large Precambrian age-provinces suggests that they were derived from two isotopically distinct mantle reservoirs. These reservoirs may be the precursors of those that exist today, a normal reservoir in the northern hemisphere and the DUPAL reservoir in the southern hemisphere. If true, the Pb isotopic composition of juvenile rocks in Precambrian age-provinces may indicate the hemisphere in which the province formed.

Coherency of Pb isotopic signatures across juvenile age provinces and the existence of two isotopically distinct reservoirs permit the use of Pb isotopes to correlate transferred terranes with potential parent cratons. If Pb isotopic compositions of juvenile Precambrian rocks are indicative of the hemisphere in which they formed, Pb isotopes may also be used to resolve ambiguity in polarity of paleomagnetic data.

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REGIONAL SCALE FLOOD MODELING USING NEXRAD RAINFALL, GIS, AND HEC-HMS/RAS: A CASE STUDY FOR THE SAN ANTONIO RIVER BASIN, TEXAS

Marla Rose Knebl Lowrey, Ph.D.

The University of Texas at Austin , 2006

Supervisor: Zong-Liang Yang

This research develops a methodology and framework for regional scale flood modeling that integrates NEXRAD Level III rainfall, GIS , and a hydrological model ( HEC -HMS/ RAS ). The case study surrounds a summer storm event over the San Antonio River Basin (about 4000 square miles, 10000 square kilometers) in central Texas , USA , a region subject to frequent occurrences of severe flash flooding. The basic model design connects a rainfall-runoff model ( HEC -HMS) with a hydraulic model ( HEC - RAS ) to model unsteady state flow. The infrastructure presented in this study extends the prototype Map to Map GIS tool to a regional scale. The preliminary model system is driven by NEXRAD 4km rainfall grids. Subsequent model experiments investigate the potential to use numerical weather forecasts of precipitation to drive the rainfall-runoff model. Results demonstrate that despite some significant errors, the calibrated model is capable of producing flood forecasts comparable to observed conditions. Addressing the heterogeneous nature of basin geomorphology and hydrology may aid in improving model accuracy. To this end, the variation in river and floodplain characteristics and their relationship to hydrologic behavior are investigated, and implications for future modeling efforts discussed. The regional scale flood model and watershed study will provide a useful tool for future flood studies over the San Antonio River Basin or similar catchments, and demonstrates the potential of increasing forecast lead time by incorporating numerical weather forecasts of rainfall into the modeling system.

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GLOBAL AND LOCAL CONTROLS ON DEPOSITIONAL CYCLICITY: CANTERBURY BASIN, NEW ZEALAND

Hongbo Lu, Ph.D.

The University of Texas at Austin, 2004

Supervisors: William Fisher, Craig S. Fulthorpe

209 pages, 296 references

The eastern margin of the South Island of New Zealand is part of a continental fragment that rifted from Marie Byrd Land in Antarctica beginning at about 80 Ma. High rates of sediment supply since the middle Miocene have resulted in the preservation of a high-frequency, seismically resolvable record of depositional cyclicity in the offshore Canterbury basin. In addition, along-strike currents have influenced deposition, modifying sequence architecture while forming large sediment drifts. High-resolution multichannel seismic (MCS) data provide insights into the interplay of global (eustastic) and local controls (tectonics and current activity) responsible for continental margin depositional cyclicity and sequence architecture.

At least eleven large, elongate sediment drifts are identified within the Neogene shelf-slope sediment prism. The drifts were deposited in water depths of 300-750 m and developed in response to a northward flowing current. Their subsequent evolution is influenced by sediment supply, relative sea-level change, and seafloor morphology. Unconformities created by paleoslope erosion at the landward edges of drift moats differ from sequence boundaries by being strongly diachronous.

Nineteen regional sequence-bounding unconformities are interpreted. Correlation with oxygen isotopic records suggests that eustasy controls the timing of sequence boundaries. In contrast, sequence thickness, shelf edge stacking patterns, internal seismic facies, and slope inclination, are strongly influenced by local processes, principally the along-strike currents responsible for drift development. Sequences with conventional clinoform geometries along strike from active drifts suggest that currents might influence clinoform formation even in locations lacking seismic evidence of current reworking.

Reconstruction of Australian-Pacific relative plate motion reveals divergence in the central Southern Alps prior to ~20.1 Ma, followed by increasing average rates of convergence, with a marked increase after ~6 Ma. Sedimentation rates, calculated from sequence volumes, correlate well with convergence rates since ~11.5 Ma, indicating that tectonism has been the dominant control on sediment supply. In particular, high rates of sediment supply since 6 Ma, may reflect previously recognized increased plate convergence and Southern Alps uplift. In contrast, high sedimentation rate from ~15-11.5 Ma correlates with low convergence rates and is therefore probably a response to global climatic forcing and eustasy.

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POLARIZATION ROTATION UPON REFLECTION OF DIRECT SHEAR
WAVES IN PURELY ISOTROPIC MEDIA

Eric Lyons, M.S.Geo.Sci.

The University of Texas at Austin, 2006

Supervisor: Robert H. Tatham

The re?ection process alters the polarization of a direct shear wave in a purely isotropic medium. I show that where the alteration occurs is governed by the shear re?ection amplitude versus incidence angle for the re?ecting interface. Speci?cally, I address the zero crossing in the S V - S V component's re?ectivity (where the amplitude changes sign), and how the zero crossing governs the alteration's location. The severity of the deviation of the polarization of the source from the observed polarization of the re?ection varies with the di ? erence in azimuth between source position and the receiver location. I develop a correction based on the observed shear amplitude versus incidence angle, which corrects to the equivalent of near-angle polarization for mid and large incidence angle (large o ? set) data. When the exact parameters from the model data are used to create the correction, the re?ected shear polarization matches the source polarization out to moderate o ? sets. A universal, model-independent correction does not perform as well as the exact correction, but it may be suitable for many applications where knowledge of regional geology is not complete. I also show preliminary results from applying the correction to anisotropic model data. The correction is most e ? ective for small percentages of anisotropy ( < 5%), after which the anisotropy signature of the observed polarization dominates over the isotropic re?ection distortion.

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TRANSPORT AND TRANSFORMATION OF SULFUR SPECIES DURING SULFURIC ACID SPELEOGENESIS: GEOMICROBIOLOGICAL SULFUR CYCLING WITHIN LOWER KANE CAVE, WYOMING

Katrina Edna Mabin, M.S. Geo. Sci.

The University of Texas at Austin, 2005

Supervisor: Philip C. Bennett

Lower Kane Cave , situated in the Madison Limestone of the Bighorn Basin, Wyoming, is forming via sulfuric acid speleogenesis. Groundwater containing dissolved sulfide and sulfate discharges into the cave, the carbonate cave walls are being replaced by gypsum, and the cave floor is covered with fallen gypsum and chert cobbles. Early conceptual models of sulfur cycling in Lower Kane Cave were limited to the autoxidation of sulfide to sulfate. The presence of a diverse community of microbial mats along the stream channels, which include sulfur-cycling bacteria, suggests that sulfur transformations within the cave are much more complex and are mediated by the microbial community. Using a suite of sampling and analytical methods, the biogeochemical sulfur cycle was investigated within aqueous, solid and gaseous reservoirs along the Upper Spring stream channel. Dissolved sulfide decreases quickly along the stream channel, and intermediate sulfoxy species are detected as well. Sediment within the main stream channel is low in total sulfur, in contrast to microbial mat biomass and deposits of processed organic material, which contain high concentrations of elemental sulfur and acid-volatile sulfur, respectively. No H 2S (g) is present in the boundary layer directly over the spring orifice, though H 2S (g) is present further downstream over areas occupied by microbial mats. Similarly, the flux of H 2S (g) from the stream surface is low near the spring orifice and higher over the mats. The overall loss of dissolved sulfide to these various sulfur species can be described by a bimolecular second-order rate equation, calculated using the initial dissolved sulfide and dissolved oxygen concentrations by the orifice, and a calculated second-order rate constant. The distribution of sulfur within aqueous, solid, and gaseous reservoirs in Lower Kane Cave is strongly associated with the presence of microbial mats. Sulfur is present along the stream channel in multiple oxidation states, indicating that both oxidation and reduction of sulfur species is occurring. The loss of dissolved sulfide from Upper Spring groundwater exceeds the loss due to volatilization or autoxidation, and suggests that microbial processes play a significant role in sulfur cycling within the cave.

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SEASONAL WATER USAGE BY JUNIPERUS ASHEI: ASSESSMENT WITH STABLE ISOTOPES OF HYDROGEN AND OXYGEN

Amy A. McCole, MS Geo Sci

The University of Texas at Austin, 2004

Supervisor: Libby Stern

The recent expansion of Juniperus ashei (Ashe juniper) on the Edwards Plateau of Central Texas has prompted studies on the impact the juniper expansion has had on the hydrologic regime of the region. This study addresses Ashe juniper's impact on the water budget of the Edwards Plateau by examining seasonal variations in the juniper's water source and the juniper's effect on soil water content at the Honey Creek State Natural Area.

The study site experiences two distinct periods of seasonal rainfall. The dry season (late spring and summer) is characterized by large infrequent storm events followed by periods of drought. The wet season (fall, winter and early spring) is characterized by large intermittent storms and smaller frequent rainfall events.

Stable isotopes of oxygen and hydrogen from precipitation, soil water, Ashe juniper xylem water, and groundwater were compared to identify the Ashe juniper water source. These data, combined with soil water content, identify different routes of soil water loss and soil water conservation as a function of vegetation cover. The USGS Bowen ratio measurements of evapotranspiration (ET), coupled with the isotope data and soil water content data, are used to partition evaporative and transpirative water loss from the terrestrial system.

Based on a mass balance calculation, a minimum of 60% of the Ashe juniper's water was obtained from groundwater over the dry season, while over the wet season, on average, only a maximum of 30% of the Ashe juniper's water was drawn from groundwater. The soil water contents, along with groundwater, soil water, and Ashe juniper xylem water δ 18Ο values, indicate that the presence of Ashe juniper can appreciably reduce groundwater resources both by lateral roots intercepting potential recharge under wet conditions and direct uptake of groundwater by deep roots under dry conditions. Additionally, Ashe juniper usage of soil water at the beginning of the grass growth season (early spring) may decrease herbaceous productivity by drawing water from beneath the grasses. Ashe juniper canopy rainfall interception is another process by which terrestrial system water is lost to the atmosphere. The isotope and soil water content data suggest that juniper canopy interception is an important route of terrestrial water loss over the wet season. Over the dry season, little evidence is seen of juniper canopy interception. Rather, the data suggest the juniper conserves soil water by limiting evaporation beneath its canopy.

ET flux measurements are separated into evaporation from the soil, evaporation from the juniper canopy, and juniper transpiration using measured ET, precipitation, soil water content, their respective δ 18Ο values, and juniper xylem water δ 18Ο values in a mass balance calculation. This unique approach shows promise for quantifying the individual components of ET water loss from the terrestrial system. More reliable results may be found when water vapor δ 18Ο values are measured and sampling occurs over shorter time intervals.

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A FIELD STUDY RECOGNIZING REDEVELOPMENT OPPORTUNITIES FOR SOUTH WESLACO FIELD, HIDALGO COUNTY, TEXAS

Andrew Dax McDavid, M.A.

The University of Texas at Austin , 2006

Supervisor: William L. Fisher

South Weslaco Field is a mature, non-associated gas field located in southeastern Hidalgo County , Texas . As of December, 2005 South Weslaco Field has produced over 151 billion cubic feet of gas from multiple Frio reservoirs contained by the 6329.15 acre South Weslaco Gas Unit (SWGU). The discovery well was drilled 1938 by the Atlantic Refining Company. Since its discovery, a total of 34 wells have resulted in seven dry holes and 27 natural gas producers. In 1997, 3-D seismic data was acquired and only one well has been drilled off existing 3-D data.

South Weslaco Field lies on the southern flank of the Norias Delta system and exhibits a mix of both aggradational and progradational deltaic sandstone reservoirs. A large down-to-the-coast growth fault creates a faulted anticline providing the main trapping feature in the upthrown and downthrown fault blocks. The upthrown fault block contributes 1.8% of the cumulative field production. These reservoirs are trapped in an upthrown three-way closure west of the growth fault. Over 98% of cumulative field production comes from reservoirs trapped in the downthrown fault block. Shallow reservoirs have four-way closure provided by an anticline that exhibits rollover into the resultant growth fault. With depth the structural crest migrates to the northeast and rollover becomes less evident.

This field study recognizes several future field development opportunities. Research has shown that the post 3-D development stage of South Weslaco Field is still in its infancy. The continued incorporation of the existing 3-D seismic data can generate various infill drilling opportunities to exploit remaining reserves. This report suggests that “new-pool” reserves can be added to South Weslaco Field from the combination of historically high gas prices, and advancements in reservoir stimulation. Deep reservoirs that have previously been deemed uneconomic can now produce economic flow rates with modern fracture techniques. From researching historic production methods employed by previous operators, this report also suggests that the possibility of remaining reserves in prematurely abandoned reservoirs.

The reevaluation of mature fields such South Weslaco can reveal opportunities for infield reserve growth. Large oil and gas companies often consider the incremental reserve growth uneconomic because of limited amount of upside hydrocarbon potential. However, the exploitation of remaining hydrocarbon reserves in mature fields can be profitable to smaller exploration and production companies.

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THE CHICXULUB IMPACT CRATER AND OBLIQUE IMPACT

Matthew A. McDonald, MSGeoSci

The University of Texas at Austin , 2006

Supervisors: Sean Gulick and Robert Tatham

Was Chicxulub an oblique (<45 degrees) impact? The answer to this question will help our understanding of the environmental consequences of the bolide that struck the Earth 65 ma in the Yucatan Peninsula . Planetary impact events, and impact simulations in the laboratory, show that oblique impacts have clear asymmetric ejecta distributions. However, the subsurface structures of the resultant craters are not well understood. From January 5, 2005 – February 19, 2005, we acquired 1822 km of seismic reflection data onboard the R/V Maurice Ewing imaging the massive (190+ km) Chicxulub impact crater to improve the understanding of subsurface crater structure and assess implications for impact obliquity. P re-crater stratigraphy outside the central basin of the Chicxulub impact crater includes packets of high amplitude reflectors on the seismic profiles, likely due to the presence of interbedded evaporite and carbonate layers. These reflective horizons are offset downward into the crater marking the post-impact slumping and formation of the terrace zone. A terrace zone forms when the overextended transient crater, which is formed by the initial impact, collapses gravitationally; large amounts of sediment, both inside and outside the transient crater, slump inward as a series of downward stepping blocks.

Can the terrace zone tell us something about oblique impact? This thesis is divided into two separate chapters addressing this question, and each will be independently submitted for publication. The first chapter presents the 3-D structure of the terrace zone based on seismic reflection data from the 2005 survey and an earlier survey done in 1996. The second chapter presents an analysis of Venusian craters addressing how oblique impacts relate to peak ring offsets. These craters are structurally comparable to Chicxulub, and the analysis implies that Chicxulub's SE peak ring offset is not related to impact trajectory. The two chapters in this thesis are mutually supportive, and suggest that the effects of oblique impact are overshadowed by other factors such as pre-impact structure and target properties. Therefore, subsurface asymmetries in the terrace zone do not appear to provide information about impact obliquity. The terrace zone, however, may help reconstruct the shape of the transient cavity and explain a concentration of ejecta toward the northwest.

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DIFFUSION, CLOSURE TEMPERATURES, AND ACCESSORY MINERAL PETROGENESES IN A HIGH-TEMPERATURE CONTACT AUREOLE: REFINING THE INTEGRATION OF P-T AND T

Christopher R. M. McFarlane, Ph.D.

The University of Texas at Austin, 2003

Supervisors: William D. Carlson and James N. Connelly

229 pages, 119 references, 0 plates

Static heating during intrusion of the 1322 Ma Makhavinekh Lake Pluton (MLP) caused replacement of garnet in the adjacent country rocks (Tasiuyak Gneiss) by coronal assemblages of orthopyroxene + cordierite. Thermometry based on Al solubility in orthopyroxene, applied to relict garnet and neighboring orthopyroxene, preserves a temperature gradient from 700°C to 900°C at distances between 5750 and 20 m from the intrusion, reaffirming the robustness of this thermometry technique. Intracrystalline and intergranular Al zoning in M2 orthopyroxene are interpreted with the aid of numerical models for conductive heat flow in the aureole. The results document the ability of Al-in-orthopyroxene thermometry to preserve a detailed record of thermal histories in contact-metamorphic granulites.

Zircon in the Tasiuyak Gneiss formed at ~1850 Ma near the peak of the Torngat Orogen (M1 metamorphism). These M1 zircons were reheated during contact heating at 1322 Ma (M2 metamorphism). U-Pb dating of M1 zircon, using thermal ionization mass spectrometry (TIMS) and in situ sensitive high resolution ion microprobe (SHRIMP) geochronology, tested whether temperatures in the aureole exceeded the closure temperature for Pb diffusion in zircon. TIMS analyses failed to resolve appreciable resetting towards 1322 Ma even in samples that reached ~900 ºC. In contrast, high spatial resolution SHRIMP data revealed that cores of M1 zircon in samples that reached temperatures >800 ºC are significantly younger than rims. This reversal of core and rim ages implies that Pb was preferentially lost from cores. This observation is hypothesized to be the result Pb migration during high temperature recovery of lattice strain induced by higher impurity concentrations (REE, P) in cores.

While M1 zircon suffered intracrystalline Pb diffusion during contact heating, it did not react with the surrounding major mineral assemblage. In contrast, low-Y monazite inclusions in M1 garnet were consumed as they were exposed to the M2 coronas. New growth of high-Y monazite records both the age and temperature of metamorphism in the aureole. Dissolution and new growth of monazite occurred under anhydrous conditions, highlighting the potential use of monazite as a high temperature thermochronometer in granulites and ultra-high temperature rocks.

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HIGH-TEMPERATURE CARBONATE REPLACEMENT MINERALIZATION, METAMORPHISM, DEFORMATION, AND INTRUSION IN THE BRYANT MINING DISTRICT, BEAVERHEAD COUNTY, MONTANA

James B. McGuire, M.S. Geo. Sci.

The University of Texas at Austin, 2003

Supervisor: J. Richard Kyle

162 pages, 52 references, plates, CD-Rom

The Bryant District, in the southwest Montana fold-and-thrust belt, contains many structurally and lithologically controlled high-temperature carbonate replacement Pb-Zn-Cu-Ag-Au deposits. Laramide crustal shortening prepared Cambrian and Devonian carbonate strata for fluid circulation through thrusting and folding. Thrust-controlled mineralization is present in the Lion Mountain mines, whereas fold-controlled chimney-style mineralization is present in the Cleve-Avon mines.

Pb isotopic evidence indicates that base and precious metals in the district were not directly sourced from phases of the adjacent Late Cretaceous Pioneer Batholith. Ore Pb was probably scavenged from the Middle Proterozoic Belt Supergroup that underlies the district. A small pluton, satellitic to the Pioneer Batholith, underlies the Hecla Dome and may have set up a hydrothermal system which produced carbonate replacement as well as Mo skarn mineralization.

Fluid inclusions in ore-associated quartz from the Bryant District are CO2-rich and have salinities from 3 to 8 wt% NaCl equivalent with homogenization temperatures from 260 to 330°C. Fluorine-deficient porphyry Mo deposits in Montana and Idaho, most notably Cannivan Gulch 5 km northwest of the Bryant District, have remarkably similar fluid inclusion characteristics, suggesting that the Bryant District carbonate replacement deposits may be the distal portion of a porphyry Mo system.

The mineralization in the Bryant District appears to be related to a late satellitic intrusion of the Pioneer Batholith. Such an intrusion was hypothesized (Winchell, 1914; Karlstrom, 1948) and recently proven by exploratory drilling on the Hecla Dome. Field evidence suggests that Pb-Zn-Cu-Ag-Au mineralization took place after most Laramide shortening, intrusion of the bulk of the Pioneer Batholith, regional metamorphism, and contact metamorphism related to the emplacement of an intrusion below the Hecla Dome.

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THE EVOLUTION OF ENDOCRANIAL SPACE IN MAMMALS AND NON-MAMMALIAN CYNODONTS

Thomas Edward Macrini, Ph.D.

The University of Texas at Austin , 2006

Supervisor: Timothy Rowe

I examined cranial endocasts of extinct and extant mammals and non-mammalian cynodonts in order to study the evolution of endocranial space in Mammalia. A cranial endocast represents the three-dimensional space within the braincase (= endocranial space). During life, the endocranial space of mammals is largely filled by the brain but also contains associated nerves, blood vessels, and meninges. Therefore, cranial endocasts provide a proxy for studying the brains of extinct mammals.

To study the evolution of endocranial space in mammals, I described new digital endocast data from four fossil mammals and a non-mammalian mammaliaform. The non-destructive nature of computed tomography allowed me to examine the cranial endocasts of these rare and unique specimens. I produced anatomical descriptions of the new cranial endocast material, and determined encephalization quotients for all of the taxa examined in this dissertation. Encephalization quotients (or EQs) are measures of the size of endocranial volume relative to body size for a particular taxon. EQs are determined from allometric comparisons of a number of closely related taxa.

Based on new endocast data combined with data obtained from the literature, I scored 39 endocast characters by incorporating data from 23 taxa. I examined these characters across a hypothesis of phylogenetic relationships for Mammalia and non-mammalian cynodonts. Examination of the distribution of these 39 endocast characters across mammal phylogeny revealed synapomorphies for the following clades: Mammalia, Monotremata, Theria, Marsupialia, and Placentalia.

The 39 endocast characters examined across mammal phylogeny were also examined in a sample of endocasts from a single mammalian species, Monodelphis domestica . The purpose of this analysis was to begin exploring the extent to which ontogenetic and individual variation of these 39 characters affects how the characters might be scored for a phylogenetic analysis. Results indicate that although there is detectable ontogenetic and individual variation among these characters when the entire M . domestica endocast sample is examined, if only qualitative characters are examined on adult specimens of Monodelphis , none of the characters are variable. Additional studies are required to determine the taxonomic extent of individual and ontogenetic variation of these characters.

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SYSTEMATIC PALEONTOLOGICAL INVESTIGATION OF THE METATHERIAN FAUNA FROM THE PALEOGENE UZUNÇARŞİDERE FORMATION, CENTRAL TURKEY

Ali Murat Maga, PhD

The University of Texas at Austin, 2008

Supervisor: Christopher J. Bell

The name Metatheria refers to the clade that contains the extant marsupials and also all extinct mammals that are more closely related to extant marsupials than to the placental mammals. Metatherians first appear in the fossil record of Asia during the Early Cretaceous, with younger records in North America (Late Cretaceous), South America (the latest Cretaceous or earliest Paleocene), and finally Australia via Antarctica (by the Eocene). The Cenozoic fossil record of metatherians in the Old World is rather poor. Except for Europe, there are only a handful of metatherian taxa known from Afro-Arabia and Asia, almost all of which are documented only by isolated teeth or partial jaws.

Fieldwork at Uzunçarşı, a fossil site in central Turkey, yielded at least three different metatherian taxa, one of which (Anatoliadelphys) is exceptionally preserved and nearly complete. In this study I demonstrate that Anatoliadelphys occupies a more derived position on the metatherian tree than the well-known South American metatherians such as Pucadelphys. My functional morphological investigations indicate that Anatoliadelphys and the South American taxa Pucadelphys and Mayulestes are different from the extant didelphid marsupials of South America in their skeletal adaptations for locomotion. Anatoliadelphys was most likely terrestrial.

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DEPOSITIONAL ELEMENT MORPHOLOGY AND ARCHITECTURE OF THE ATOKA INTERVAL, FORT WORTH BASIN, TX, U.S.A.

Vishal Timal Maharaj, M.S. Geological Sciences

The University of Texas at Austin, 2008

Supervisor: Lesli J. Wood

The Atoka Group (Lower-Middle Pennsylvanian) of the Fort Worth Basin (FWB) forms a significant (~2–3 Tcf), and as yet underexploited, domestic gas resource that is often seen as a secondary target as operators make their way to the deeper Barnett Shale. Although thousands of wells penetrate the Atoka in the FWB, the origin and character of this unit are still debated. The influence of deeper Ellenburger karsting on depositional morphology and element character has also been insufficiently addressed. Current depositional model interpretations vary from wave-dominated, to river-dominated, to fan deltas, comprising various braided, meandering, and mixed-load stream systems.

An understanding of the facies in the Atoka and their spatial distribution can be enhanced by utilizing the most effective tool in describing each level of resolution (seismic/low, well log/medium, core/high) and producing methods of correlation that accurately define the geometries that exist. A 3-D survey covering 68 km2 of the FWB has been integrated with data from 226 wells and core from 3 wells for detailed mapping of the Atoka. In seismic, the Atoka is represented by a ~200-ms interval showing geometric relationships of lapout (onlap, offlap, toplap, downlap, and truncation), which suggest the existence of imageable geomorphic features. Both seismic and well log mapping show that the Atoka can be subdivided into 12 parasequences that stack to form: (a) a lower, regressive; (b) a middle, transgressive; and (c) an upper, highstand parasequence set. Core analysis reveals that eight main facies exist in the Atoka, which suggest the interval comprises a series of coarse-grained, fluvio-deltaic and shallow marine deposits. Criteria are outlined for defining channel dimensions using point bar measurements from well logs, and a detailed quantitative analysis of the variability of these dimensions in cross-section and plan-view was undertaken. Point-bar analyses indicate that channel widths range from 34 to 456 m, given the variability in both local and regional accommodation space created during deposition. A review and comparison of modern and ancient analogs to Atoka sediments support the interpretation of a river-dominated delta system. The argument is reinforced by observations from facies components identified in core, gamma-ray-log expressions, and the distant location of the study relative to highland sources. Previous fan- and wave-dominated delta interpretations are therefore discounted and do not apply to the study area.

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ARCHITECTURE AND SEISMIC GEOMORPHOLOGY OF SHELF EDGE DELTAS ALONG AN ACTIVE TECTONIC MARGIN, EASTERN OFFSHORE TRINIDAD

Julie Anne Maher, M.S. GeoSci

The University of Texas at Austin, 2007

Supervisor: Lesli J. Wood

144 pages, 72 references, 15 tables

The South American continental margin, offshore eastern Trinidad and Venezuela, has a Tertiary and near-modern history of shelf margin sedimentation, with architecture and morphology influenced by margin tectonics. Influences include strike-slip faulting; compressional folding; extensional, counter-regional faulting; and upper-slope-graben development. A ~2,600 km2 3D-seismic data volume containing nearly 75 km of shelf margin shows that the Orinoco Delta prograded to the ancient shelf edge, developing significant shelf edge deltas. The last Plio/Pleistocene deltaic regression and transgression were mapped using seismic tied to 14 well logs. Key surfaces were mapped and packages defined. Intervals were isopached to examine thickness changes along the shelf. Attributes (amplitude, semblance, root-mean-squared amplitudes, etc.) were analyzed to map seismic geomorphology of shelf and slope systems. Analysis included deltaic clinoform trajectory, slope-channel sinuosity and density, and fault character. We wanted to examine shelf-edge-structural influence on sources of deep-water sands and the relationship between delta architecture, fault character, and slope morphology.

Observations showed that delta sediment bound for deep water during the last glacial maximum became trapped in upper-slope minibasins formed by down-to-the-basin normal and counter-regional growth faults. Only in the northernmost end of the study area where the counter-regional fault dies out did shelf edge deltas prograde onto the upper slope.

Three types of shelf edge delta trajectories were identified: aggradational, progradational, and over-steepened. Over-steepened is associated with the highest density of bypassing channels and aggradation with the lowest. Most channels are straight—except on lower-angled slopes downdip of the progradational province, where channels show sinuosity. Channel densities from aggradational and over-steepened provinces decrease basinward of the shelf break and fault; progradational province channel densities remain constant or increase. Areas of higher fault throw correspond to downdip development of large numbers of bypass channels. However, areas downdip of over-steepened provinces show high concentrations of bypass channel development regardless of fault-throw associations. These data suggest that slope-channel frequency is closely tied to clinoform trajectory, with high clustering associated with progradational/over-steepened regions. Tectonics affect these more-unstable-trajectory regions to increase downslope sediment movement. Lower channel frequencies downdip suggest more aggradational, tectonically stable clinoforms proximally.

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THE GENETIC ASSOCIATION BETWEEN BRITTLE DEFORMATION AND QUARTZ CEMENTATION: EXAMPLES FROM BURIAL COMPACTION AND CATACLASIS

Astrid Makowitz, Ph.D.

The University of Texas at Austin, 2004

Supervisors: Earle F. McBride and Kitty L. Milliken

298 pages, 182 references, 1 CD

Brittle deformation of quartz grains accompanied by quartz cementation is a porosity-reducing mechanism in sandstones. Brittle deformation has historically been overlooked as a mechanism of compaction because it has been poorly understood and techniques for observing it are not commonly used. I have used scanned cathodoluminescence (CL) to quantify brittle deformation of quartz grains, in sandstones undergoing burial and cataclasis.

Sandstone samples of different ages and compositions, taken from two basins with contrasting burial histories, are used to examine the interaction between brittle deformation and quartz cementation in burial compaction. Trends of increasing deformation by microfracturing with maximum burial depth are observed in both the lithic-rich Frio Formation from the Gulf of Mexico basin and in the quartz-rich Mount Simon Formation of the Illinois basin. Combining information on the degree of brittle deformation and the amount of quartz cement localized within microfractures allows for the calculation of the amount that brittle deformation influences compaction (i.e. porosity loss). For the Frio, 0.12 to 8.37% of initial porosity is lost due to cementation related to brittle deformation, whereas the values for the Mount Simon lie between 0.25 and 2.16%.

Diagenetic forward models are constructed for each formation using petrographic modal analysis and burial history information to determine the depth of quartz cement commencement as an influential factor affecting brittle grain deformation. Most fracturing probably occurred prior to the precipitation of > 2% quartz cement. Commencement of quartz cementation at shallow depths combined with slower burial rates resulted in less brittle deformation in the Mount Simon compared with the Frio, where sandstones underwent rapid burial and quartz cementation began at greater depths.

Cataclastic sandstones within the Pine Mountain Overthrust, eastern Kentucky, show more extreme porosity reduction by fracturing and cementation than normally compacted sandstones. In contrast to normal burial compaction, cataclasis and cementation within the cataclasites occurred over several discrete episodes as evidenced by cross-cutting relationships of fractures and cement. Quantitative data on the distribution of inter- and intragranular quartz cement within cataclasized sandstones combined with CL observations show that the timing of deformation is in agreement with published dates of fault movement.


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THE ANISOTROPIC SEISMIC STRUCTURE OF THE EARTH'S MANTLE: INVESTIGATIONS USING FULL WAVEFORM INVERSION

Eric M. Matzel

The University of Texas at Austin, 2002

Supervisor: Stephen P. Grand

132 p, 93 refs, 0 plates

I have developed a waveform inversion procedure to invert 3 component broadband seismic data for models of the anisotropic seismic structure of the Earth and applied the technique to an investigation of wave propagation through anisotropic media and earthquake data sampling the upper mantle beneath the East European platform. The procedure combines the conjugate-gradient and very fast simulated annealing methods and attempts to minimize a cross-correlation misfit function comparing data to synthetic seismograms. A series of inversion passes are performed over a range of frequency and time windows to progressively focus in on structural details. The intent is to obtain P and S velocity models that simultaneously match all components of the data (radial, vertical and tangential). The variables in the problem are the seismic velocities (á and â) as a function of depth. When radial anisotropy is required this set is expanded to include the five variables that determine the seismic velocities in a radially anisotropic medium (áh, áv, âh, âv, ç).

I investigate the propagation of seismic waves through radially anisotropic media, evaluate which elements of radial anisotropy are best resolved by seismic data and discuss strategies for identifying radial anisotropy in the Earth. S anisotropy, â%, and the horizontal component of P velocity, áh, are typically well resolved by multicomponent seismic data. P anisotropy, á%, and ç are often poorly resolved and trade off with one another in terms of their effect on Sv arrivals. Erroneous structure will be mapped into models if anisotropy is neglected. The size of the erroneous structure will be proportional to the magnitude of anisotropy present and extend well below the anisotropic zone. The effects of anisotropy on P models produced with an isotropic assumption are most similar to the effects on isotropic SH models. When comparing isotropic models, á/âSH, is therefore often a better measure than á/âsv for characterizing mantle petrology. Isotropic SH, SV and P models developed separately using the same data set can provide a good initial estimate of the presence, location and magnitude ofanisotropy and those results can be used to create an initial model for an

anisotropic inversion solving simultaneously for all 3 components of the data.

Finally, I present models for the P and S velocity structure of the upper mantle beneath the East European platform including an analysis of radial anisotropy. The data are 3-component broadband seismograms from strike-slip earthquakes located near the edge of the platform and recorded in Russia and Europe. The timing, amplitude and interference characteristics of direct arrivals (S, P), multiply reflected arrivals (SS, PP), converted phases and surface waves provide very good radial resolution throughout the upper 400 km of the mantle. The platform is underlain by a radially anisotropic seismic mantle lid extending to a depth of 200 km with a largely isotropic mantle below. The model has a positive velocity gradient from 41 km to 100 km depth, and a relatively uniform velocity structure from 100 km to 200 km depth with high SH and PH velocities (4.77 km /s, 8.45 km/s). Shear anisotropy is uniform at 5% (âH > âV) from 41 to 200 km depth, drops to 2% from 200 to 250 km and is isotropic below that. The average shear velocity from 100 to 250 km is also uniform at 4.65 km/s and the drop in anisotropy is matched by a drop in âH to 4.70 km/s combined with an increase in âV to 4.60 km/s. Below 250 km there is a positive velocity gradient in both P and S velocity down to 410 km. P anisotropy is not well resolved, but P structure mimics the SH velocity structure, suggesting that P is also anisotropic within the lid.


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TECTONICS OF THE HJORT REGION OF THE MACQUARIE RIDGE COMPLEX, SOUTHERNMOST AUSTRALIAN-PACIFIC PLATE BOUNDARY, SOUTHWEST PACIFIC OCEAN

Timothy Ashworth Meckel, Ph.D.

The University of Texas at Austin, 2003

Supervisors: Sharon Mosher and Millard F. Coffin

230 pages, 152 references, 0 plates

The Hjort Ridge, Trench, and Plateau comprise the southernmost portion of the Macquarie Ridge Complex (MRC), the Australian-Pacific plate boundary south of New Zealand. The MRC is an ideal location to study deformation and structural development at an obliquely convergent plate boundary involving oceanic lithosphere. This dissertation documents structures and processes in the Hjort region associated with incipient subduction, an outstanding problem in plate tectonics.

I investigated the evolution of the plate boundary from ~33 Ma to the present day, concentrating on the active and recent structural development. Interpretations are based on analyses of recently collected geophysical data in the Hjort region, including swath bathymetry, reflectivity, seismic reflection, gravity, magnetics, and seismicity. The Australian plate is actively underthrusting the Pacific plate along the Hjort Trench, but self-sustaining subduction does not appear to have commenced.

Transpression along the length of the plate boundary has been accomodated by lithospheric flexure, strike slip faulting, and geographically limited underthrusting. A consistent relationship exists between the convergence angle and the amount of dynamically supported topography; up to 50 km of convergence has been accomodated by flexure forming ridges and troughs. A continuous, strike slip fault accomodates oblique convergence along the length of the boundary. Where angles of convergence are highest (>20o), underthrusting is observed in addition. Gravity modeling and seismicity suggest ~50 km of underthrusting in the southern Hjort Trench, but only define an eastwardly dipping Australian slab to about 20 km depth. Lithosphere underthrust in the southern trench is translated subparallel to the ~N-trending boundary, limiting the eastward extent of underthrust slab.

Reconstructions of the plate boundary since 33.3 Ma show that the Antarctic-Australian-Pacific triple junction migrated southward with respect to the Australian plate resulting in the present day curved plate boundary. Migration resulted in lengthening of the dextral transform fault connecting the Macquarie Ridge and Southeast Indian Ridge spreading centers and shortening of the easternmost ridge-segment of latter spreading center. The MRC in the Hjort region changed from a dextral transform into an obliquely convergent zone of incipient subduction.

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COGENERATION: A TECHNOLOGY REVIEW AND A TECHNICAL AND ECONOMIC EVALUATION OF ITS INTEGRATION INTO THE CEMENT INDUSTRY

Carolos Medina, MA

The University of Texas at Austin, 2002

Supervisor: Willem C.J. van Rensburg

Rapid deregulation and privatization in all energy markets are pushing some industry sectors towards small-scale power production opportunities that offer attractive returns on their investments. To this extent, several regional industrial development organizations and governments around the world have recognized that fuel-efficient power generation technologies such as Cogeneration can help increase energy efficiency.

Cement production is one of the largest and most energy-intensive industry sectors, both on fuel and power. With increasing electric energy costs, and considering that the cement-making process involves large amounts of waste heat that could otherwise be used for a subsequent process, bottoming-cycle Cogeneration has proven to be an attractive, cost-effective solution for in-house power generation. This research illustrates some experiences with Cogeneration in the cement industry, and explores the principles of its economic feasibility.

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THE ORIGIN OF MODERN QUARTZ ARENITE SANDS ON BEACHES OF THE FLORIDA PANHANDLE

Joseph L. Mehring, M.S. Geo. Sci.

The University of Texas at Austin, 2005

Supervisor: Earle F. McBride

Along 400 km of coastline, Panhandle of Florida beaches are composed of quartz arenites ( >99 % quartz) with little variation in composition except west of the Mobile River. Florida Panhandle beaches are the only known modern quartz arenite sands in North America. They are an anomaly: modern quartz arenite sands are nearly all found in tropical settings where there is intense chemical weathering, whereas Florida is in a temperate setting.

Beach samples were collected along the Gulf Coast from Apalachee Bay, FL on the east, to Mobile Bay, AL on the west. River sands were collected in Georgia, Alabama, the Florida Panhandle, and Eastern Mississippi. These rivers traverse bedrock ranging from Precambrian basement rocks to Paleozoic, Cretaceous, Tertiary, and Quaternary sedimentary rocks. Sandstones from Cretaceous to Pleistocene age that crop out in the study area were sampled from five wells. River, beach, and cuttings samples were analyzed using point counting to determine average composition, quartz grain types, and average quartz roundness. In addition, the SEM was used to examine surface textures and cathodoluminescence (CL) was used to look for recycled authigenic quartz

In spite of draining source areas of diverse types of bedrock (basement rock to unconsolidated sediments), rivers that feed the Florida Panhandle beaches have quartz arenite compositions as far as 170 km inland. The quartz arenite composition of the river samples reflect increasing amounts of dilution of sand from basement rocks with recycled quartz-rich sand from Tertiary and Quaternary sandstones towards the coast. However, even Cretaceous sandstones are 86 to 98 % quartz.

The presence of non-spherical quartz grains with essentially unmodified sharp, angular edges is in keeping with Kuenen’s (1960) hypothesis that neither river nor beach abrasion can round sand-size quartz. However, I cannot say that some rounding did not occur. There is no average roundness trend for beach samples from east to west and there are only increases in the well-rounded quartz population towards the east. Trends for the beach samples are controlled by westward shoreline drift and sediment input from rivers feeding the coast. Rivers show an increase in average roundness towards the coast. Based on quartz grains containing evidence of abrasion and authigenic quartz, beach samples are inferred to be approximately 96 % recycled.


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THE ARCHITECTURE OF LOWER-SLOPE CHANNEL COMPLEXES, OFFSHORE GABON, WEST AFRICA

Rosalba Mendoza-Veloza, M.S. Geo. Sci.

The University of Texas at Austin , August 2007

Supervisor: William L Fisher

Turbidite successions in deep-water settings along passive margins are hosts to prolific volumes of hydrocarbons around the world. Recent discoveries in the West Africa margin have reinforced the success of this type of play. It is, however, still considered immature and carries great exploration risks and high development costs. Amongst the highest risks are the uncertainties in the architecture and the reservoir distribution, and the inherent internal heterogeneities of the reservoirs themselves. Advances in seismic imaging technology and geological modeling techniques have improved our understanding and ability to map these systems.

This study has documented the presence of a vast variety of turbidite systems of Late Oligocene to Late Miocene age on the northern margin of the Congo Fan. The turbidite deposits in these systems exhibit distinct seismic reflection patterns that allow identification of three megastratigraphic successions: (1) The Upper Oligocene succession, composed of continuous to moderately continuous low-amplitude reflectors; (2) the Lower Miocene succession, made up of low-continuity low-amplitude reflectors with isolated packages of highly discontinuous reflectors; (3) the Middle to Upper Miocene succession, which consists of a combination of highly discontinuous high-amplitude reflectors and moderately continuous moderate-amplitude reflectors. Calibration of seismic data to well-log data demonstrates the correlation between high-amplitude reflection pattern with sand-prone channel-fill facies, the moderate-amplitude reflectors with levee facies, and the low-amplitude reflectors to hemipelagic clay-rich deposits.

Three main channelized architectural styles have been identified in the three stratigraphic succession: (1) The single-thread channel (Type1) of low sinuosity and poorly developed channel-levees is the simplest style and is the main component of the Upper Oligocene succession formed in a relatively erosional system fed by mud-rich currents; (2) channel belts made up of high-sinuosity channels that are laterally stacked and fed by mud-sand rich currents (Type 2); and (3) channel belts made up of sinuous erosional and aggradational channels amalgamated in a complex stacking pattern and fed by sand-rich turbidity currents (Type 3). The Type 2 and Type 3 are the main components of the Miocene successions.

Salt tectonism played a role in the channel-architecture evolution. Salt-generated seafloor deformation produced turbiditic flow confinement and deviation in places, as well as local modification in the paleo-slope, alteration of sinuosity patterns and sourcing of debris flow.

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EXTRAPOLATION OF ELASTIC AND PETROPHYSICAL PROPERTIES FROM WELLS USING 3D PRESTACK SEISMIC AMPLITUDE DATA

Germán Diego Merletti, M.S.Geo.Sci.

The University of Texas at Austin , 2006

 

Supervisor: William L. Fisher & Carlos Torres-Verdín

This thesis describes the successful application of a new pre-stack stochastic inversion algorithm to the spatial delineation of thin reservoir units otherwise poorly defined with deterministic inversion procedures. The inversion algorithm effectively combines the high vertical resolution of wireline logs with the relatively dense horizontal coverage of 3D pre-stack seismic amplitude data. Multiple partial-angle stacks of seismic amplitude data provide the degrees of freedom necessary to estimate spatial distributions of lithotype and P- and S-wave velocities in a high-resolution stratigraphic/sedimentary grid. In turn, the estimated volumes of P- and S-wave velocity permit the statistical co-simulation of lithotype-dependent spatial distributions of porosity and permeability.

The new stochastic inversion algorithm uses a Bayesian maximization criterion to populate values of lithotype and P- and S-wave velocities in the 3D simulation grid between wells. Property values are accepted by the Bayesian selection criterion only when they increase the statistical correlation between the simulated and recorded seismic amplitudes of all partial-angle stacks. Furthermore, inversion results are conditioned by the predefined measures of spatial correlation (variograms) of the unknown properties, their statistical cross-correlation, and the assumed global lithotype proportions.

Using field data acquired in a fluvial-deltaic sedimentary rock sequence, it is shown that deterministic pre-stack seismic inversion techniques fail to delineate thin reservoir units (10-15m) penetrated by wells because of insufficient vertical resolution and low contrast of elastic properties. By comparison, the new stochastic inversion yields spatial distributions of lithotype and elastic properties with a vertical resolution between 10-15m that accurately describe spatial trends of clinoform sedimentary sequences and their associated reservoir units.

Blind-well tests and cross-validation of inversion results confirm the reliability of the estimated distributions of lithotype and P- and S-wave velocities. Inversion results provide new insight to the spatial and petrophysical character of existing flow units and enable the efficient planning of primary and secondary hydrocarbon recovery operations.


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DIFFUSION-CONTROLLED GROWTH FROM A HETEROGENEOUS PRECURSOR: GARNET CRYSTALLIZATION AT PASSO DEL SOLE, SWITZERLAND

Charna Elyse Meth, MS Geo Sci

The University of Texas at Austin, 2002

Supervisor: William Carlson

Whereas previous studies of mechanisms controlling metamorphic crystallization have focused principally on garnets growing in the absence of strong deformation, this work examines syn-deformational garnet growth in a regional metamorphic environment. Analysis of compositional zoning of garnets in a single sample of pelitic schist from the northern margin of the Lucomagno nappe, near Passo del Sole, Switzerland, indicates that the garnets' rate of radial growth was proportional to their size. This relationship has not been previously documented for porphyroblasts but is consistent with diffusion-controlled growth of garnet from a heterogeneous matrix.

Qualitative X-ray mapping on surfaces passing through the morphological centers of 23 garnets (located using high-resolution X-ray computed tomography) reveals extremely unusual calcium zoning. In every garnet, regardless of size, the inner portion of the garnet gradually increases in calcium concentration, and the outer portion contains fine-scale oscillatory zoning. The oscillations are contemporaneous in all garnets, judging from two lines of evidence: sigmoidal inclusion trails intersect a distinctive band of high Ca just before the inclusion trails begin to curve; and the composition of garnet at this distinctive band is identical in every crystal.

The radial distance between two compositional zones in a garnet crystal is indicative of the rate of radial growth of the crystal integrated over a specific time interval. For the 20 garnets mapped on central sections, five different growth intervals were identified from correlated Ca oscillations. Mn profiles for eight garnets were divided into 16 growth intervals defined by identical Mn contents. Both Ca and Mn were used as time markers. The radial width of each growth zone was measured and compared with the mean radius during the corresponding growth interval. The results for Ca and Mn reveal a positive correlation between the radius of a crystal and its radial rate of growth. This is demonstrably different from the results expected for diffusion-controlled growth from a homogeneous matrix (a negative correlation) and interface-controlled growth (a slope of zero).

Size-dependent growth of this kind has not previously been identified in metamorphic minerals, although it has been reported for cathodoluminescent zoning in dolomite crystals, for diagenetic quartz overgrowths, and for crystals grown from stirred solutions. Theoretical mechanisms for size-dependent growth are typically based on surficial characteristics, such as the presence of dislocations as favored sites for growth. Although such characteristics might have had a minor influence on the growth of the garnets at Passo del Sole, to explain their size-dependent growth by that means would require continuous introduction of surface dislocations to maintain a higher surficial dislocation density in the larger crystals than the smaller crystals during growth, a scenario that seems implausible in this instance.


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CONTROLS ON THE STABLE ISOTOPIC COMPOSITION OF SPELEOTHEMS, BARBADOS, WEST INDIES

Patrick John Mickler, Ph. D.

The University of Texas at Austin, 2004

Supervisors: Jay Banner and Libby Stern

161 pages, 135 references

Applications of speleothem calcite geochemistry in climate change studies require the evaluation of the accuracy and sensitivity of speleothem proxies to most correctly infer paleoclimatic information. The present study of Harrison’s Cave, Barbados, uses the analysis of the modern climatology and groundwater system to evaluate controls on the C and O isotopic composition of modern speleothem calcite. This new approach directly compares the δ 18O and δ 13C values of modern speleothem calcite formations with the values for their corresponding drip waters in order to assess the degree to which isotopic equilibrium is achieved during calcite precipitation.

Carbon isotope values for the majority of modern speleothem calcite samples from Harrison’s Cave fall within the range of equilibrium values predicted from the combined use of 1) calcite-water fractionation factors from the literature, 2) measured temperatures, and 3) measured δ 13C values of the dissolved inorganic carbon of drip waters. Enrichments and depletions in 13C, relative to equilibrium C isotopic compositions, are also observed. The 13C depletions are likely caused by kinetically driven departures in the fractionation between HCO 3 - (aq) and CaCO 3 from equilibrium conditions, caused by rapid calcite growth. 13C enrichments can be accounted for by Rayleigh distillation of the HCO 3 - (aq) reservoir during degassing of 13C-depleted CO 2.

In contrast to the C isotopic results, most modern speleothem calcites from Harrison’s Cave are not in O isotopic equilibrium with their corresponding drip water and are enriched in 18O relative to equilibrium values. δ 18O variations of modern calcite are likely controlled by kinetically driven changes in the fractionation between HCO 3 - (aq) and CaCO 3 from inferred equilibrium conditions to non-equilibrium conditions, consistent with rapid speleothem calcite growth. In contrast to δ 13C, the effects of Rayleigh distillation on the δ 18O values of modern calcite are buffered by CO 2 hydration and hydroxylation reactions that influence the O isotopic composition of the HCO 3 - (aq) reservoir. The effects of Rayleigh distillation manifest themselves in samples taken along a growth layer by producing a progressive enrichment away from the growth axis with a constant δ 13C vs. δ 18O slope. This observation has significance to ancient speleothem studies. A review of the literature has found that 62% of 141 studies show positive δ 13C vs. δ 18O correlation consistent with our non equilibrium models.


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SEPARATING STRUCTURAL FROM DEPOSITIONAL COMPLEXITY IN THE PALEOCENE LOWER WILCOX “LOBO” SANDS, ZAPATA COUNTY, TEXAS

Sarah Diana Milewski, BA

The University of Texas at Austin, 2007

Supervisor: Ronald J. Steel

100 pages, 57 references, 9 tables

The Lobo Trend of Webb and Zapata Counties, Texas, lies in the northern part of the Gulf of Mexico Basin and is part of the Lower Wilcox (Late Paleocene) stratigraphic unit that is observable across South Texas. The informally named slumped and faulted deposits of the lowermost Wilcox Group, the Lobo Trend, is comprised of wave-dominated deltaic and shoreface deposits which consist of various lobes of well-developed fine-grained, tight sandstone. Subsequent structural complexity makes the unraveling of the original sedimentary complexity a challenge.

The Lower Tertiary deposits of the Lobo series average 800 feet thick (Claughton, 1977) and represent progradational shallow-marine shoreface sands. These deltaic and shoreface sands were part of larger deltaic systems with sediment derived from the north and west (Fisher and McGowen, 1967; Galloway et al., 2000). Through both fluvial and longshore transport sediment accumulated as shoreline sands in the mid- to outer-shelf in the Gulf of Mexico Basin. These sands subsequently underwent severe disruption and faulting in response to large-scale postdepositional slumping.

In many locations the Lobo sandstones provide a quality reservoir rock for oil and gas accumulation. More than 4.5 Tcf of natural gas have been produced from the sands of the Lobo Trend (Anno et al., 2002), and development operations continue today, making the Lobo of great interest to many individuals and companies. Stratigraphic and sedimentologic studies on the area, however, are severely hampered by structural intricacies, and as a result, studies of the depositional history and stratigraphy of the area have been limited.

This study focuses on the main Lobo sand lobe packages present in northeastern Zapata County, Texas. The dataset consists of 3-D seismic coverage, well logs, thin section samples, and core data. Stratigraphic and structural cross-sections have been generated from the integrated dataset to help define the depositional history and stratigraphic framework of the study area and sequence stratigraphic concepts from both the Galloway model and the Vail (Exxon) model have been applied. To evaluate possible provenance of these sands, a petrographic study was performed. Additionally, a workflow model has been designed for the interpretation of this data, with the aim of separating the structural from the depositional components of complexity, thus providing further regional understanding and prediction of the Lobo series in northern Zapata County.<\p>


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STRUCTURAL FRAMEWORK AND DEPOSITIONAL SYSTEMS OF A COMPLEX RIFT AND STRIKE-SLIP PLATE MARGIN: BLOCKS CI-104 AND 105, IVORY COAST, WEST AFRICA

Thomas E. Miskelly, Jr., M.S.Geo.Sci.

The University of Texas at Austin, 2002

Supervisor: William E. Galloway

A 3D seismic data set was used to analyze the structural framework and depositional systems of a Cretaceous extensional basin adjacent to a Cretaceous strike-slip margin active during the opening of the Equatorial Atlantic Ocean. 1800 km2 of data was collected by Petroleum Geo-Services in 1986 and covers blocks CI-104 and 105 offshore of the Ivory Coast. The complex structure in the area of interest is a prolongation of strike-slip faulting along the St. Paul fracture zone to the southwest and is similar to rotated fault blocks described by previous workers on the eastern side of the Ivory Coast basin. Previous studies and the Ocean Drilling Project (ODP) cores near the Ivory Coast-Ghana Ridge east of my study area show the slope and base-of-slope sedimentary rocks to be primarily siliciclastic.

Four tectono-sedimentary phases were identified and related to Cretaceous extensional tectonics: 1) pre-rift Aptian lacustrine phase, 2) Aptian-Albian active rift phase, 3) late Cretaceous thermal uplift phase, and 4) late Cretaceous and Tertiary post-rift passive margin phase. The Aptian pre-rift and Aptian-Albian syn-rift phase exhibit tilting and strike-slip of the fault blocks during the rifting. The thickness of the pre-rift sedimentary rocks total 0.4 seconds two-way-time (TWT), while the post-rift rocks average 5 seconds TWT in the central basin. The geometric patterns of the structural features were analyzed and show similarities with observed and modeled strike-slip tectonics in other areas.

The late Cretaceous and Tertiary post-rift deposits were transported by gravity into the base-of-slope environment within a narrow graben formed between tilted rift blocks. Seven, laterally-extensive unconformities were interpreted from seismic data and are tied to the 3492-m-deep K1-2X well. The age of the unconformities corresponds to the age of regressions identified on a eustatic sea level curve for the Gulf of Guinea. These unconformities separate the Jurassic pre-rift sequence, Aptian-Albian sequence, late Cretaceous sequence, Paleocene-Eocene sequence, Oligocene sequence, early Miocene sequence, and Upper Miocene-Pleistocene sequence. Post-rift depositional facies (e.g. slumps, channel complexes, drapes) and erosional features (e.g. canyons, bypass unconformities) were imaged in the seismic survey. Chaotic, convergent, and drape seismic facies differentiate among sedimentary facies and were identified and mapped using seismic facies analysis. The post-rift paleogeographic maps show a submarine channel complex, interpreted to provide the bulk of the sandy reservoir facies, flowed southwesterly during the late Cretaceous and early Tertiary and changed to a more southerly orientation in the Upper Miocene-Pleistocene sequence.


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A GEOCHEMICAL INVESTIGATION OF THE FORMATION AND EVOLUTION OF THE RIO GRANDE RIFT

Julie Leeanne Mitchell, B.S.

The University of Texas at Austin, 2008

It is hypothesized that lithosphere beneath the Rio Grande rift was thinned after the Laramide orogeny as a result of adiabatic upwelling of asthenosphere in response to rollback of the Farallon plate. Spinel peridotite xenoliths from two localities were studied to gauge whether lithospheric thinning took place. The presence of spinel constrains the depth of formation of the xenoliths to 60 km or less; if asthenosphere is detected, the lithosphere will likely have thinned to at least 60 km (from an original thickness of 100km). Cerro Chato, a locality that sits along the south-western edge of the Colorado Plateau, and Elephant Butte, which is along the axis of the Rio Grande rift, were compared. Textural, major-element, and two-pyroxene geothermometric analyses of spinel peridotite xenoliths were conducted for each locality. Kil and Wendlandt (2004) proposed that texture can be used to estimate the depth of formation of a peridotite. However, such a trend was not seen in this study, and texture has been rejected as a means of estimating depth. Because the Colorado Plateau is a region of very thick lithosphere, it displays a cold and depleted major-element signature; it was expected that Cerro Chato would be similar. Additionally, the Basin and Range is known to have experienced lithospheric thinning, with asthenosphere likely close to the crust, causing a hot, fertile signature. It was expected that Elephant Butte would be similar to the Basin and Range. Contrary to those hypotheses, Elephant Butte was in fact similar to both Cerro Chato and the Basin and Range, while Cerro Chato was both hotter and more fertile than the Colorado Plateau. This study concludes that the lithosphere beneath the Rio Grande rift has not been thinned to less than 60 km. It is possible that thinning in the lithosphere took place at or near 60 km, which would explain the similarities in temperature and composition between Cerro Chato and Elephant Butte. However, trace-element and isotopic analyses, in addition to more extensive geothermometric analyses of Elephant Butte, are required to more fully answer the questions posed by this study.

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CONTROLS ON THE MORPHOLOGY AND DEVELOPMENT OF DEEP-MARINE CHANNELS, EASTERN OFFSHORE TRINIDAD AND VENEZUELA

Kristine Lynn Mize, M.S. GeoSci

The University of Texas at Austin, 2004

Supervisors: Lesli Wood and William Fisher

Deep marine channel and levee architecture has a consistent and predictable geometry that is strongly influenced by seafloor slope.  This steady state geometry is altered by changes in seafloor bathymetry in a predictable manner.

There is little understanding of how deep-water channel systems and their reservoir and non-reservoir elements evolve in structurally-complex settings. This study looks at slope-levee channel systems offshore eastern Trinidad, which act as sediment transfer conduits, moving sediment from the Orinoco Delta to the basin-floor Orinoco fan. The morphology and architecture of these systems is strongly influenced by slope gradients and by a number of active mud diapirs that occur as the result of sediment loading and thrusting in this area. Morphology is defined as values that change temporally and spatially, such as sinuosity, meander belt width, and radius of curvature. Channel-levee architectures can be compared spatially using the cross-sectional features of the channel: thalweg, levees, and overbank splays. Quantitative seismic geomorphology (QSG) has been applied to collect an immense temporal and spatial database of the channels’ morphologies and architectures. QSG is used to quantify the geomorphology of a system to produce interpretations derived from seismic data to identify depositional systems and associated depositional elements. The quantitative data are used for assessment of changes in the channels’ morphology and architecture, and for producing predictive models of channel architecture based on cumulative probability plots.

Results of this study indicate that the eruption of mud diapirs through the seafloor surface directly changes the morphometrics of a deep-marine channel. Increases in sinuosity, radius of curvature, and meander belt width, along with decreases in channel width and depth are observed immediately downslope of mud diapirs. Channel architecture is severely affected as levees are thinned and are forced to pinch-out up the flanks of the diapirs. Cumulative probability plots are used to present the P10, P50, and P90 values, which provide the range in which morphologies and architectures are likely to fall. Each of these values represents the likelihood that a certain characteristic will occur. For class A or highly sinuous channels in the mud diapir-rich system, probability (P10-P90) values range from 1.1-1.8 for sinuosity and 125-440 meters for channel width. High-sinuosity turbidite channels and their deposits are associated with increased sand percentages and are a target for petroleum exploration. Cumulative probability plots of critical channel morphologic and architectural elements act as predictive models that assist in addressing uncertainty and minimizing risk in locating similar channel systems in analogous structural regimes.

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CHARACTERIZATION OF A SANDSTONE FRACTURED RESERVOIR: FROM CORE TO 3D SEISMIC ANALYSIS TACATA FIELD, NORTHERN MATURIN BASIN, VENEZUELA

Patricia Montoya, M.S.

University of Texas at Austin, 2002

Supervisor: William Fisher

The detection and characterization of natural fracture properties in the subsurface can determine the economic potential and appropriate development strategy of a reservoir. Fractures can have a high impact on oil and gas exploration and production because they introduce heterogeneities into the reservoir and can be major fluid flow conduits. Thus, a good understanding of the theoretical fundamentals, classification, description and analysis of natural fractures is necessary.

At present, several methods can be used to describe and analyze natural fractures. One of these methods uses cores as direct geological samples of fractures. The microfractures are imaged with a scanning electron microscope (SEM) and described by using cathodoluminescence detectors, which allow observations that are not viable using conventional microscopic techniques. When sufficient amounts of data are recorded, microfracture orientations can be obtained and they reproduce the orientation detected at macroscopic scales where this is possible by using cores.

However, cores are just a small part of the puzzle that can help in the identification and measurement of fracture sets. Because cores represent only a very small portion of any reservoir, other methods can provide a more regional view of fractures. In this regard, indirect methods such as 3D P-wave AVAZ (amplitude variations with azimuth) seismic analysis can help to determine important properties of the fractures. This technique works because it detects azimuthal elastic anisotropy due to parallel vertical fractures embedded in an isotropic matrix. From this analysis, fracture orientation and relative intensity maps can be generated entirely from subsurface observations and they can be verified by comparison with the results obtained from core analysis.

For this study, a fractured Tertiary sandstone reservoir located in the northeastern part of the Maturin Basin in Venezuela was chosen. The main problems were to determine if the fractures are connected or isolated, and to identify attributes such as orientation and intensity from an oriented core and a 3D P-wave seismic survey. Thus, from micro- and macrofracture analyses from the core (at Well 5) two sets of fractures were detected. The main set of open fractures strikes at an azimuth of 100º, and a second set striking at 40º, interpreted as closed. Additionally, from the 3D P-wave AVAZ seismic analysis, a fracture orientation map was generated showing the main set of fractures strikes at an approximate azimuth of 101º, and a secondary set at 41º, at the position of Well 5. On the other hand, the fracture intensity map shows several NW-SE zones having high fracture intensity, separated by areas of intermediate to low intensity.

In conclusion, both core and seismic techniques derived the same orientations of dominant fracture sets, at least around the location of Well 5, proving the high potential of P-waves to detect fracture effects on seismic wave propagation. Also, the relative fracture intensity map showed that there are some connected areas separated by areas with lower intensity of fractures, indicating possible preferred fluid flow paths due to the presence of fractures.


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SALT TECTONICS AND SEQUENCE-STRATIGRAPHIC HISTORY OF MINIBASINS NEAR THE SIGSBEE ESCARPMENT, GULF OF MEXICO

Patricia Montoya, Ph.D

The University of Texas at Austin , 2006

Supervisors: William L. Fisher and Michael R. Hudec

The focus of this research is to understand the stratigraphic and structural evolution of lower-slope minibasins in the Gulf of Mexico by examining the influence of salt tectonics on sediment transport systems and deep-water facies architecture.

Results showed that gravitational subsidence and shortening can cause variations in the relief of salt massifs on opposing sides of a minibasin. These bathymetric variations, combined with changes in sedimentation rates through time, affected not only the distribution of deep-water facies inside the minibasins, but also influenced the evolution of sediment transport systems between minibasins.

In order to understand the evolution of salt massifs, this dissertation presents a new approach to evaluate qualitatively the rate of relative massif uplift based on depoaxis shifts and channel geometries identified in minibasins surrounded by mobile salt. From these results it was established that compression was long-lived, and that extension only dominated during late intervals.

Stratigraphic analyses showed that there is a strong cyclicity in deep-water facies stacking patterns within lower-slope minibasins, related primarily to cyclical changes in sedimentation rates. A typical sequence starts with a period of slow sedimentation associated with drape facies above each sequence boundary. Then, towards the middle and final stages of the sequence, sedimentation rates increase and turbidity flows fill the minibasin.

Previous studies describe processes of fill-and-spill for two adjacent minibasins in the upper and middle slope. However, these models fail to adequately explain fill-and-spill processes in lower slope minibasins surrounded by mobile salt. In particular, they do not consider the effect of variations in bathymetric relief of the intervening massif, nor do they examine multidirectional connections between proximal and distal minibasins. A new dynamic-salt fill-and-spill model is proposed in this dissertation in order to understand the origin and distribution of sediment pathways and variations in connection styles. In this model, connection styles are controlled by changes in salt massifs relief and sedimentation rates through time. Four connection styles exist between minibasins: no connection, wide connection, narrow connection and bypass connection. Low sedimentation rates tend to shut down connection between minibasins, whereas high sedimentation rates favor development of pathways that connect minibasins.

In summary, the most important contribution from this research is that variations in salt-massif relief, combined with changes in sedimentation rates through time, can yield different filling histories and connection styles for nearby minibasins. So by understanding the influence of these factors, the complicated task of identifying sediment pathways in salt-controlled environments can be attempted in a more effective way.

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SEQUENCE STRATIGRAPHIC FRAMEWORK AND SYSTEMS TRACTS ANALYSIS OF LOWER MIOCENE SHELFAL CLASTIC DEPOSITS: REDFISH BAY AREA, TEXAS GULF COAST

Brian T. Moore, MSGeoSci

The University of Texas at Austin, 2005

Supervisors: William L. Fisher and Robert G. Loucks

The deposits of the Lower Miocene section of the Redfish Bay area along the Texas Gulf Coast were characterized and their systems tracts and depositional environments were interpreted. A three-dimensional seismic volume and associated wireline-logs were used in an analysis of base-level changes and in the characterization of third-order sequences within the Lower Miocene stratigraphic section, which includes highstand, transgressive, and lowstand-incised-valley systems tracts. The Lower Miocene interval in the Redfish Bay study area consists of four unconformity bounded third-order sequences. The oldest sequence, sequence I, contains a lowstand systems tract (LST), transgressive systems tract (TST), and highstand systems tract (HST). The above-lying sequence II is similar to sequence I. The next two younger sequences in the Miocene interval, sequences III and IV, contain only the TST and HST. Emphasis has been placed on the LST incised-valley deposits in this study as the origin of the sand that makes up this system tract has been debated for years.

LSTs contain a higher net-sand thickness to gross interval thickness ratio, relative to the TSTs and HSTs. There is a decreasing sand-percentage trend from LST to TST to HST in the lower two sequences. A decreasing sand-percentage trend from TST to HST continues in sequence III. In sequence IV there is an increasing sand percentage trend from TST to HST.

The deposits of the LST of sequence I are interpreted as incised-valley fill. The incised-valley fill contains higher-frequency sequences, within the third-order LST, composed of amalgamated fluvial deposits and transgressive estuarine deposits. The TST of sequence I displays more wave-dominated and more wide-spread sand deposits than the LST. Depositional systems encountered in the HST are progradational deltas and interlobe deposits. The lowstand amalgamated fluvial deposits and transgressive estuarine sediments, which filled the incised-valley of the third-order LST of sequence II, were deposited during higher-frequency cycles. The interbedded stratigraphy of the high-frequency sequences within this LST suggests that it has much more estuarine influence than the LST of sequence I. The deposits of the TST of sequence II are more dominated by destructive processes than the deposits in the LST. Depositional systems composing the HST are difficult to discern, but are interpreted as having been deposited in a shallow-water, mud-rich environment. Within sequence III, no LST incised valley deposits are recognized from the wireline-log patterns or in the seismic data. It is also evident from the wireline-logs that the TST and HST in sequence III are very sand poor.

The TST of sequence IV had more sand influx relative to sequence III. As indicated by wireline-log analysis, fluvial depositional systems dominate the TST and HST. The variability in the amount of amalgamation of fluvial channels within the systems tracts suggests that the fluvial system is responding to relative base-level fluctuations. In the TST, the fluvial channels range from more amalgamated sand bodies at depth where rate of relative base-level rise is lowest, to less amalgamated sand bodies with an increasing rate of relative base-level rise. In the HST where relative base-level was already high, the fluvial channel sand bodies become less amalgamated following the maximum flooding event. As the relative rate of base-level rise decreases in the HST, the fluvial channel sand bodies become more amalgamated.

Integration of wireline-log characteristics, structural mapping from 3-D seismic data, isopach mapping between third-order erosional surfaces, and analysis of seismic stratal slices, demonstrate the existence of dip-oriented, incised-valley depositional systems within the LSTs of sequences I and II. The Lower Miocene stata in the study area were deposited twenty miles up-dip of the Late Oligocene shelf-edge. The recognition of incised-valley systems is important for understanding the sequence stratigraphic framework and the origin of thick, massive sands of the Lower Miocene deposits of the middle Texas Gulf Coast. The incised-valley systems are also important because they transported Lower Miocene sediment to deepwater areas.


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QUARTZ CEMENTATION MODELING AND RESERVOIR QUALITY OF THE UPPER CRETACEOUS SANDSTONES IN CARITO FIELD, NORTH MONAGAS, VENEZUELA

Julymar M. Morantes, MS Geo. Sci.

The University of Texas at Austin, 2003

Supervisor: Earle F. McBride

180 pages, 57 references

The Carito oil field in the Sub-Maturin Basin of Eastern Venezuela in the northern part of Monagas State produces hydrocarbons from Upper Cretaceous and Tertiary sandstones. This study was conducted using cores and samples of sandstones from four third-order sequences in the Carito field in order to: 1) reconstruct the diagenetic evolution, including porosity evolution of the sandstones; 2) quantify the relative importance of porosity loss by compaction and cementation by quartz, the main cement; and 3) determine whether a forward-modeling reservoir-quality application (Touchstone) can be used successfully in a foreland basin setting.

Core samples were available from four third-order sequences, sequence T1 in the Tertiary and sequences K1, K2 and K3 in the Upper Cretaceous. Sandstones were deposited mainly in deltaic environments with variable tidal influences, although continental and shallow-marine depositional environments are also represented. Sandstone composition ranges from Q64F1.6R34.4 to Q100R0F0 (average Q90R3F7). Average detrital quartz in the four sequences ranges from 64 to 78% of framework grains. Felsitic volcanic rock fragments and feldspars make up less than 6.1 % of framework grains. In order of decreasing abundance, quartz overgrowths, hydrocarbons (not a true cement), illite, kaolinite, and mixed-layer clays, pyrite, and dolomite (locally important) occur as cement within the pore space regardless of the stratigraphic framework of those sandstones. Quartz cement averages for each third-order sequence ranges between 5.9 and 10.8% and dominates over clay minerals, such as kaolinite and illite. Dolomite cement and replaced grains are abundant in four samples.

Porosity averages for the four sequences, range from 6.7 to 9.1 %; primary porosity is greater than secondary porosity except for sequence T1. The lowest average porosity value occurs in sequence K2 owing to its large amount of mineral cement (average 14.8%). Permeability measurements on core plugs reveals fair to high reservoir quality; 57%, 91%, and 86% of the samples for sequences K1, K3 and T1 respectively, have permeability values ranging from 5 mD to >500 mD. In sequence K2 80% of analyzed samples have fair to poor quality reservoir. IGV values overall range from 5% to 46%; average values for sequences ranges from 13.4% to 17.8%. These values are indicative of porosity loss chiefly by grain rearrangement but some porosity was also lost by brittle fracture and pressure solution. Average values of porosity loss by compaction (COPL) ranges from 32.5% to 36.5% and are larger than values of porosity loss by cementation (CEPL) which ranges from 5.9% to 11.1%.

The most important diagenetic processes were mechanical compaction, quartz cementation, partial or complete dissolution of feldspar grains and felsitic volcanic rock fragments, and kaolinite precipitation. Fluid inclusions show that oil emplacement was later than the main phase of quartz cementation. Main controls on amounts of quartz cement are the amount of clay-coats (inverse relationship), temperature history, and sandstone composition. K-feldspar and kaolinite distribution are a function of the sequence stratigraphic framework. Samples from sequence K1 have a larger amount of kaolinite and a lesser amount of K-feldspar than other Cretaceous sequences and marks a regional mineralogical change (SB-K2) that probably reflects an influx of meteoric water and subsequent replacement of feldspar by kaolinite.

The evolution of intergranular volume (IGV), intergranular porosity, and quartz cement, were simulated from the time of deposition to the present using Touchstone " and data from 45 samples from four wells (A,B, C and D). Modeling results show a good agreement between petrographic data and predicted values, suggesting that this method can be applied to sandstones in structurally complex basins typical of this study. Modeling supports the observation that mechanical compaction plays the most important role in decreasing primary porosity and IGV from the time of deposition through the passive margin stage (Late Cretaceous to Early Miocene). Quartz cementation began to form around 60 Ma at very slow rate; this small amount of quartz cement was not enough to prevent porosity loss by mechanical compaction. Around 20 Ma the sediments reached the appropriate temperature (80°C) and precipitated significant amounts of quartz cement. The rate of cementation accelerated during the past 10 Ma because of tectonic accretion and thrust emplacement in the Furrial area.

The best reservoir quality is present in medium- to coarse-grained sandstones from sequences K3, K1, and T1 at burial depths from 4,200 to 4,800 km and coarser. Sandstones buried more than 4,800 km have total porosity values lower than 4%, the lowest IGV values, and the highest amount of cement and replacement.

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DETRITAL ZIRCON GEOCHRONOLOGY AND PETROLOGY OF THE FRANCISCAN GRAYWACKE BLOCKS AT SAN SIMEON: IMPLICATIONS FOR MÉLANGE GENESIS

Anna Marie Morisani, M.S., Geological Sciences

The University of Texas at Austin , 2006

Supervisor: Mark Cloos

The Central Mélange Belt of the Franciscan comprises a tectonically produced mixture of graywacke blocks with lesser amounts of greenstone, chert, and graphite schist blocks, in a shale matrix. Rare exotic blocks of blueschist and eclogite are also found dispersed within the Central Belt exposures. South of San Francisco, it is exposures at San Simeon that give the best sense of the chaotic nature of mélange.

The nature of mélange formation has been debated since Hsu (1968) applied the term to describe the chaotic rocks in the central California Coast Ranges. The age of the most common type of block in the Franciscan mélange, graywacke, has never been directly determined. Knowing the depositional age of the ubiquitous graywacke blocks at San Simeon will provide new constraints on the origin of mélange. The age distribution obtained in the process will reveal a new understanding of the character of the source terranes of the sediment being fed to the trench.

Petrographic information obtained from mélange graywacke blocks in this study includes the occurrence of pumpellyite in many samples, indicating temperature and pressure conditions consistent with depths of 10-15 km in an active subduction zone with subnormal geothermal gradients. Thin sections also revealed the pinch-and-swell structure of mélange graywacke blocks was attained by particulate flow. The style of deformation in the mélange graywacke blocks as well as the generation of pumpellyite is consistent with the process described in the flow mélange model.

On the basis of age distributions obtained for the 16 mélange graywacke block samples analyzed in this study, three groups have been identified: Graywacke Group One (12 samples), Graywacke Group Two (two samples), and Graywacke Group Three (two samples). The timing of deposition for Graywacke Group One has been constrained to a window between 87 and 92 Ma. The timing of deposition for Graywacke Group Two has been constrained to between 84 and 87 Ma. The timing of deposition for Graywacke Group Three has been constrained to between 119 and 127 Ma.

New age data for two samples of the Bedded Slope Cover (135-140 Ma), one sample of the Green Sand Unit (123-126 Ma), and two samples of Graphite Schist (175-183 Ma) has also been obtained. Additional constraint on the maximum age of the Bedded Slope Cover comes from two interbedded ash layers, with dates of 148 Ma and 150 Ma .

The age data has shed new light on the model of mélange emplacement at San Simeon. Two scenarios are proposed to account for the new petrographic and age information obtained in this study. Sediment was transported to the trench axis, subducted to depths of 10 to 15 km, and then returned towards the surface where it was accreted. The three Graywacke Groups are interpreted to represent three distinct phases of mélange generation and or diapirism at San Simeon. The second scenario postulates that all three Graywacke Groups were deposited at the trench axis and subsequently subducted and deformed together. The variable age data is the result of the complexities of sedimentation at the trench axis.

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A GENERALIZED REFLECTIVITY APPROXIMATION FOR P-P AND P-S V AVO

Matthew Graham Morris, B.S.

The University of Texas at Austin, 2003

Supervisor: Robert Tatham

87 pages, 25 references

In order to adequately characterize a reflected seismic wave as a function of incidence angle, the raypath geometry and energy partitioning must be considered separately. While ray theory can provide an amenable solution for raypath geometry, the partitioning of energy at an interface is a complex phenomena to describe in mathematical terms. The Zoeppritz equations are a set of four simultaneous equations used to describe the reflections of a plane wave. Since these equations are both cumbersome and highly nonlinear, several useful approximations have been developed that provide a more intuitive understanding of amplitude versus offset (AVO) behavior. The Shuey approximation, (Rpp(Θ) ≈ B0 + B2sin2Θ) and the Ramos approximation, (RPS(Θ) ≈ B1sinΘ + B3sin3 Θ) are predicated on the assumptions that media contrasts and incidence angles are relatively small. As these assumptions are increasingly violated, the efficacy of these two-term approximations begins to diminish.

To account for these discrepancies, an expanded form of the Shuey/Ramos approximations is proposed. This form, termed the ‘generalized polynomial approximation,' contains all of the lower order B i sin i q terms that are normally omitted when performing curve fitting in amplitude-sin q space. The effects of these additional terms are studied.

For a population of 625 modeled interfaces, the median error for all of the Shuey/Ramos AVO coefficients is reduced substantially when the generalized polynomial approximation is compared to the standard Shuey/Ramos approximations. The additional terms appear to exhibit differing dependencies on the lithologic parameters V P , V S , and r when the fractional change is large across the interface.

A case study supports the trends in these observations. A four-component marine seismic dataset is used to quantify the performance of the generalized polynomial approximation on P-P and P-S V data. The P-P B 0 and P-S V B 1 and B 3 terms are all mildly affected by the inclusion of additional lower order terms The P-P B 2 term is profoundly affected by the additional terms, suggesting that the Shuey approximation is yielding an incomplete description of the actual data.

The preceding observations suggest that the generalized polynomial approximation may be used to complement traditional two-term AVO approximations. When the additional lower order terms yield values that materially deviate from zero, the small-contrast assumption inherent to the Shuey and Ramos approximation is likely being violated. As such, the generalized polynomial approximation can help to identify incongruencies between the AVO curves observed in seismic data, and their respective two-term approximations.

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MASS TRANSPORT PROCESSES AND DEPOSITS IN OFFSHORE TRINIDAD AND VENEZUELA, AND THEIR ROLE IN CONTINENTAL MARGIN DEVELOPMENT

Lorena Gina Moscardelli, PhD

The University of Texas at Austin, 2007

Supervisor: Lesli Wood

172 pages, 115 references, 3 tables

Mass transport complexes (MTC) form a significant component of the stratigraphic record in ancient and modern deep water basins. One such basin, the deep marine margin of eastern offshore Trinidad, situated along the obliquely converging boundary of the Caribbean and South American plates and proximal to the mouth of the Orinoco River, is characterized by catastrophic shelf margin processes, intrusive and extrusive mobile shales, active tectonics and possible migration and sequestration of hydrocarbons. Major structural elements found in the deep water slope regions include: large transpressional fault zones along which mobile shales extrude to form seafloor ridges; fault-cored anticlinal structures overlain by extrusive seafloor mud volcanos; shallow-rooted sediment bypass grabens near the shelf break; and normal and counter-regional faults. A data volume consisting of 10,708 km2 of several merged 3D seismic data volumes enable subseafloor interpretation of several mass transport event deposits and the erosional surfaces that form their boundaries. The data shows numerous mass transport complexes which are characterized by chaotic, mounded seismic facies and fan-like geometries. Their extent (up to 2017 sq. km) and thickness (up to 250 m) is strongly influenced by seafloor topography. Depositional and erosional architectures identified with these units includes: large magnitude lateral erosional edges, thrust faulting, linear basal scours, side-wall failures, flow geometries, possible displaced blocks and chaotic matrix material. Active tectonism in the region, high sedimentation rates associated with the Orinoco Delta System, and abundant unstable gas hydrates suggest the presence of higher frequency mechanisms at work for MTCs generation than sea-level fluctuations alone.

Three types of mass transport complexes are identified in offshore Trinidad; shelf- attached systems that were fed by shelf edge deltas whose sediment input is controlled by sea level fluctuations, slope- attached systems which occur when upper slope sediments catastrophically fail due to gas hydrate disruptions, earthquakes and/or storm activity, and locally detached systems formed when local instabilities in the sea floor trigger small collapses. Such classification of the relationship between slope mass failures and the sourcing regions enables an understanding of the nature of initiation, length of development history, petrography and petrophysics of MTC’s.

In addition, a collection of morphometric parameters of MTCs from different continental margins are analyzed in order to better understand their causal mechanisms, and to establish whether systematic morphometric parameters characterize these deposits across different tectonic settings. Observations suggest that there is a clear relationship between morphometric parameters of MTC and their causal mechanisms.

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A KINEMATIC INVESTIGATION IN THE CRIPPLE CREEK DISTRICT, CENTRAL COLORADO: IMPLICATIONS REGARDING THE STRUCTURAL CONTROLS INFLUENCING THE LOCATION AND DISTRIBUTION OF GOLD ORE ZONES

Alison Suzanne Mote, MS Geo Sci

The University of Texas at Austin, 2004

Supervisors: J. Richard Kyle and Tim Wawrzyniec

181 pages, 77 references, 1 CD-Rom, 1 plate

The Cripple Creek epithermal deposit is a historic gold camp located at the southern end of the Colorado Front Range in central Colorado. Mineralization in the Oligocene-aged alkaline volcanic center is characterized by high-grade Au-telluride bearing veins and disseminated deposits. The purpose of this investigation is to evaluate the tectonic conditions during volcanic development and test the kinematic influence on the location and distribution of high-grade ore zones. Results of this investigation reveal that structural development, dominated by strike-slip faulting, played an integral role in the location and distribution of high-grade ore concentrations.

Fault kinematic data illustrate that NE-directed shortening influenced early structural development of the deposit, and the main phase of structural development occurred during a transitional tectonic regime, between the waning stages of Laramide contraction and the onset of Rio Grande Rift-related extension. Sub-vertical strike-slip faults moving in response to this extensional tectonic regime were the most efficient pathways for mineralizing fluids. Fault kinematics indicate that faults that contain low-grade mineralization in the NE portion of the deposit formed early (in response to NE-directed shortening) and were not favorable pathways for mineralizing fluids. The NW-striking Cresson fault is the most prominent structural feature in the district. This large-scale right-lateral fault (associated with E-W extension) is interpreted as a high-permeability zone that served as a conduit for large volumes of fluid flow through the district. Fault kinematics show that fractures in Riedel shear geometries were forming during dextral slip along the fault zone. These fractures appear to have allowed fluids to escape along this zone of high permeability, where physiochemical changes in the ore-bearing fluids resulted in the precipitation of gold from solution, forming high-grade ore zones. In-situ measurements of grains within a high-grade sheared vein were produced using high-resolution X-ray computed tomography. Three-dimensional analysis of telluride grains indicates a preferential distribution of major and minor axis orientations, suggesting that telluride mineral fabric orientations are related to shear zone kinematics. Volumetric data indicate that more than half of the grade in the sample is derived from a small percentage of grains, i.e. 60% of ore grade is derived from 17% of the grains, or the largest grains.

 

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SEISMIC DATA PROCESSING IN TRANSVERSELY ISOTROPIC MEDIA: A PLANE WAVE APPROACH

Anubrati Mukherjee, Ph.D.

The University of Texas at Austin, 2002

Supervisors: Paul L. Stoffa and Mrinal K. Sen

Occurrences of anisotropy in the seismic data are widespread at all scales. Thus inclusion of these anisotropic effects becomes important for obtaining correct images and target depths. This dissertation addresses some problems pertaining to seismic data processing in transversely isotropic media. I have formulated an interactive traveltime analysis procedure for P-waves in delay-time, slowness domain for wave propagation in the transversely isotropic media with a vertical axis of symmetry (VTI). Using the assumption of weak anisotropy I obtained a simple and physically intuitive two-term expression for vertical slowness, which can be used in direct estimation of interval elliptic velocity and the anisotropic parameter kappa. I have also developed a method to automatically estimate these parameters using a non linear inversion technique called very fast simulated annealing.

Conventional ray tracing methods are difficult to apply in the VTI media. Unavailability of vertical P wave velocity restricts us to use the time gridded elliptic velocity and kappa as inputs for traveltime computation in offset-time domain. However I have formulated a ray tracing technique based on the Fermat's principle and perturbation theory. The method uses phase velocities unlike other methods, which use group velocities. Head wave paths are not included in the traveltime computation. Comparison with more exact Finite Difference Eikonal solvers for both 1-D and 2-D models show small residuals.

I have used source traveltimes computed using the interval elliptic velocity and kappa models to perform prestack split-step Fourier and Kirchhoff time migration in the VTI media. Migration using parameters estimated from moveout analysis and computed source traveltimes for Gulf of Mexico data show good results. The common image gathers show increased flattening after incorporation of anisotropic effects.

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EFFECTS OF TAXONOMIC AND LOCALITY INACCURACIES ON BIOSTRATIGRAPHY AND BIOCHRONOLOGY OF THE HUESO AND TAPIADO FORMATIONS IN THE VALLECITO CREEK–FISH CREEK SECTION, ANZA-BORREGO DESERT, CALIFORNIA

Lyndon Keith Murray, Ph.D.

The University of Texas at Austin, 2008

Supervisor: Christopher J. Bell

The fossiliferous sediments of the Hueso and Tapiado formations exposed in the Vallecito Creek-Fish Creek section (VCFC) of the Anza-Borrego Desert (ABD) span the boundary between Blancan and Irvingtonian North American Land Mammal 'Ages.' Historically, the determination of the Blancan-Irvingtonian (B-I) boundary in the VCFC proved problematic.

A new study to determine the B-I boundary in the VCFC revealed data inaccuracies in both published works and curatorial records of the mammal and other vertebrate fossils from the ABD. Most individual inaccuracies were minor, but an accumulation of over 50 years of multiple inaccuracies had significant effects on local and regional biostratigraphic and biochronologic correlations. A detailed investigation of the inaccurate data resulted in recognition of 17 types of error, with at least five sources. The two most prominent sources of error are those derived from publication and curation protocols. Examination of over 150 publications and in-house faunal lists produced over 830 taxonomic names and format variants, for 110 mammalian taxa identified from the ABD and VCFC. Approximately 50% of the taxonomic identifications were previously published without voucher catalogue numbers or fossil descriptions. A critical review of the taxonomic assignments resulted in an updated faunal list of ABD terrestrial Mammalia, including 110 taxonomic names, 66 unqualified genera, and 46 unqualified species. A supplemental list of 'retired' taxa includes 178 previously published or listed taxonomic names and format variants.

The 4.5 km sequence of originally superposed sediments within VCFC is now tilted at 23 degrees and exposed in plan view. This exposure was captured in both aerial photos and satellite imagery. GIS layers of the Geomagnetic Polarity Time Scale and individual collecting localities are readily superposed onto the stratigraphic images. When united with the faunal database, GIS maps of biostratigraphic data facilitate detection and correction of data errors. Resulting corrected maps show highest and lowest stratigraphic occurrences of taxa, as well as geographic clustering of taxonomic groups, outlining possible paleohabitats. As a result of data improvement and GIS display, the local B-I boundary currently is best estimated by the presence of Ovibovini at >1.42 Ma.

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RELATIONS AMONG SEDIMENTATION, DIAPIRISM AND CAP ROCK FORMATION AT THE DAVIS HILL SALT DOME, LIBERTY CO., TEXAS

Asif Muzaffar, M.S. Geo. Sci.

The University of Texas at Austin, 2001

Supervisor: J. Richard Kyle
Co-Supervisor: Bruno C. Vendeville

The Middle Jurassic Louann evaporites played an important and complex role in creating structure and providing traps for hydrocarbon accumulation in response to sedimentation and ongoing subsidence of the Gulf of Mexico basin. Like other domes in the Gulf of Mexico region, the Davis Hill salt dome is the result of salt response to sedimentation. The Davis Hill dome is a relatively large structure, encompassing an area of more than 5 mi2 and emplaced within the siliciclastic-dominated sediments of the Gulf of Mexico Basin. The eastern margin of the dome and the cap rock have had several oil tests, only few wells were drilled on the western side of the dome; however oil was only found on the eastern side of the dome. Only one well penetrated the Wilcox section on the eastern side of the dome, thus limiting the study of deeper strata and the interpretation of the earlier history of the dome.
The main phase of diapir growth took place during the deposition of the Wilcox Group. The thickness of the entire Wilcox Group varies between 12,000 and 16,000 ft (~3600 to 4800 m), with a local thickening of 4,000 ft (~1200 m) within the salt withdrawal basins. The rate of dome growth during the lower Wilcox deposition was about 1,511 ft/M.y. (0.46 mm/y) and decreased to 1,333 ft/M.y. (0.4 mm/y) during middle and upper Wilcox. After deposition of the Wilcox Group, the growth rate decreased substantially to 257 ft/M.y. (0.08mm/y) during the Lower. Claiborne. There was a marginal increase to 325 ft/M.y. (0.01 mm/y) during Yegua deposition, 308 ft/M.y. (0.093 mm/y) during Jackson, and 271 ft/M.y. (0.082 mm/y) during the Vicksburg. Subsequently, the crest of the dome was buried by Frio and post-Frio sediments.
The presence of cap rock at the Davis Hill dome is evidence of the dissolution of salt over an extended period of time. Studies of cores indicate that the cap rock is about 440 ft (~138 m) thick and consists of anhydrite, gypsum and calcite zones from the anhydrite-salt contact upward. The anhydrite zone represents the less soluble components of the salt that was accumulated as the halite was dissolved by pore fluids. The anhydrite zone locally contains abundant celestite that probably formed as the result of interaction with external Sr-bearing brine. The calcite zone was formed by bacterial alteration of sulfate that accompanied hydrocarbon destruction. The calcite zone contains significant amounts of sulfide minerals and oil. The sulfide-rich calcite zone is approximately 40 ft thick and dominated by locally massive iron sulfides. These sulfide concentrations resulted from the interaction of deep heated metal-bearing formational brines with bacterially derived reduced sulfur in the ambient cool ground waters.
The systematic accumulation of anhydrite cap rock layers by underplating occurred when the salt diapir was dissolved, allowing a cap rock stratigraphic succession to be defined on the basis of texture and accessory minerals. These relationships were used to constrain the timing of the dome growth and cap rock formation.
The growth rate for cap rock accretion during downbuilding and upbuilding was about 7 ft / M.y. (0.0021 mm/y), reflecting an average rate of cap rock accretion during dome growth.

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A TEXTURAL EXPLORATION OF THE PHYSICAL ATTRIBUTES OF PUMICE FROM THE 23,000 Y.B.P. ERUPTION OF POPOCATEPETL VOLCANO IN CENTRAL MEXICO

Nicole Rose Myers, M.S. Geo. Sci.

The University of Texas at Austin , 2006

Supervisor: James Gardner

The focus of this textural study of pumice is on understanding why volcanic eruptions produce pumice with a range of vesicularity and discerning which processes of an eruption are recorded in pumice. Our study uses pumice produced during the White Pumice eruption of Popocatepetl Volcano in Central Mexico 23,000 Y.B.P. to document the vesicularities, volumes, sizes, shapes, and spatial orientations of bubbles in pumice.

The bulk vesicularity of the White Pumice ranges from 55 to 88 vol.%, with a mean value of 75 vol.%. We characterize the textural attributes of relatively low, medium, and high vesicularity pumice . Bimodal bubble-size distributions (BSDs) suggest that with increasing bulk vesicularity, the large bubbles increase in vesicularity, whereas the small bubbles have fairly consistent vesicularities. Bubble-number densities (BNDs) reveal that there is a general decrease in the BND of large bubbles (in clasts = 65 vol.%) with increasing vesicularity, while small bubbles have relatively constant number densities (in clasts = 65 vol.%). These observations suggest that small bubbles grow and coalesce to ~45 vol.% vesicularity and then discontinue evolving, while large bubbles continually evolve with increasing bulk vesicularity. The exception to these observed trends is a 60 vol.% vesicularity clast, which has a low large BND and high small BND, which suggests less bubble growth and coalescence occurred compared to higher vesicularity samples.

A continuum in bubble shape from contorted to round to elongated with increasing vesicularity also suggests differential growth of bubbles in low vesicularity pumice in comparison to bubbles in high vesicularity pumice. Bubble orientations reveal a preferred alignment of vesicles, which we attribute to laminar flow direction in the conduit. The preferred alignment is increasingly overprinted with increasing vesicularity, providing evidence of differing degrees of bubble evolution through bubble growth and coalescence.

These textural continua can be explained by a fragmentation sequence model that takes advantage of differing degrees and timing of permeability within the ascending bubbly magma to gradually fragment the flow. With the initiation of the fragmentation sequence in the volcanic conduit at ~64 vol.% vesicularity, the vesiculated magma begins to break apart into individual pumice. We suggest that the 60 vol.% vesicularity clast broke away from the bubbly magma in the first round of fragmentation, and thereby efficiently degassed relatively early causing bubble growth to stop. Pumice of progressively higher bulk vesicularity are fragmented later and therefore experienced gas loss relatively later during (or after) fragmentation, thereby allowing more time for bubble evolution. As a result, variations in vesicularity are partially caused by variations in permeability within the pre-fragmentation conduit flow allowing some fragments to break away relatively early, and on the timing of efficient degassing in the rest of the bubbly magma as fragmentation continues. The range in vesicularity produced by a single eruption can therefore be attributed to pre-fragmentation evolution of heterogeneously distributed permeable networks causing a range of bubble shapes, followed by fragmentation gradually exposing fragments of higher vesicularity, which allows for longer periods of evolution that gradually overprint evidence of pre-fragmentation flow processes.

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MAPPING HYDRAULIC CONDUCTIVITY OF THE OGALLALA AQUIFER IN TEXAS

Thet Naing, M.S.

The University of Texas at Austin, 2002

Supervisors: John M. Sharp, Jr. and Alan R. Dutton

The Ogallala aquifer in Texas provides large amount of water for both municipal and irrigation uses. Since groundwater development in 1950's, water level in the Ogallala has declined significantly. In many parts, the saturated thickness of the aquifer is reducing. Numerical groundwater flow models are used to assess groundwater availability of the aquifer and require an immense number of spatial data. Quality of input data determines accuracy of flow simulation results. Model results are sensitive to hydraulic conductivity. Long-time pumping tests give the best estimate of hydraulic conductivity. However, these tests are expensive and rarely conducted. On the other hand, specific capacity data from well performance tests are more abundant and can be converted to hydraulic conductivity using analytical relationships between specific capacity and transmissivity. The goal of this study is to map hydraulic conductivity of the Ogallala aquifer in Texas to aid in providing input data for the groundwater flow modeling especially for the areas where data are not available. For the study area, 115 measurements from long-term pumping tests or core analyses and 7397 measurements from specific capacity tests are collected. The data from both data sets are combined and analyzed together. Calculated hydraulic conductivity values are log-normally distributed. The geometric mean of combined hydraulic conductivity data is 6.3 ft/day (2.2´ 10-5 m/s), with a minimum value of 9´ 10-3 ft/d (3.2´ 10-8 m/s), maximum value of 2644 ft/d (9.3´ 10-3 m/s), and median value of 7.8 ft/d (2.7´ 10-5 m/s).

Hydraulic conductivity is a spatially correlated geologic variable. Hydraulic conductivity values of the study area were mapped by kriging interpolation and hand-contouring. Variogram modeling and kriging methods are used in an attempt to incorporate spatial relationship in the interpolation. Measured hydraulic conductivity data are best fitted by non-directional, isotropic exponential model. Results indicate that interpolated hydraulic conductivity values correspond to mapped sand-gravel percent values. Therefore, in places where aquifer sediment information is absent, it could be inferred from interpolated hydraulic conductivity. The calculated hydraulic conductivity data are also hand-contoured based on collected data, net thickness and percentages of sand-gravel, and elevation of the basal Ogallala. Hand-contoured map show similar but narrower trends of high hydraulic conductivity trend as in the interpolated maps.


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THE CRANIAL OSTEOLOGY OF ANGOLOSAURUS SKOOGI (SQUAMATA: GERRHOSAURIDAE) WITH COMMENTS ON THE MORPHOLOGY AND PHYLOGENY OF THE CORDYLIFORMES

Holly Anne Nance, M.S. Geo. Sci.

The University of Texas at Austin, 2003

Supervisor: Christopher Bell

233 pages, 90 references, color illustrations, CD-Rom

Phylogenetic relationships both within and between the scincomorph families Gerrhosauridae and Cordylidae are in need of reexamination. Currently, the basal gerrhosaurid is unknown, although Angolosaurus skoogi previously was proposed as the basal member of mainland African gerrhosaurids. Many details of the cranial osteology of A. skoogi are unknown because of the rarity and elusive lifestyle of this dune-dwelling lizard, endemic to the Namib Desert. In this study, I utilized High-Resolution X-ray Computed Tomography (HRCT) to study in detail the cranial osteology of A. skoogi. Results of this study enabled me to complete the first anatomical description of the skull and mandible of A. skoogi. This description is accompanied by a fully labeled cross-sectional CT data set. I used these data to search for new cranial osteological characters, and provide a tentative hypothesis regarding the phylogenetic position of A. skoogi within Gerrhosauridae. With the CT data, and disarticulated skeletal preparations, I rescored cranial osteological characters from previous phylogenetic analyses and discovered 25 new characters. Results from my tentative analysis support the basal position of Angolosaurus within Gerrhosauridae. However, the discovery of new characters has further-reaching implications for morphological analyses. Detailed cranial osteology obtained from CT data and disarticulated specimens proved to be a valuable source of phylogenetically-informative characters.

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DESIGNING NATURAL GAS SUPPLY PORTFOLIOS USING MEAN-VARIANCE TOOLS

Peter Kevan Nance, M.A.

The University of Texas at Austin, 1993

Supervisor: Martin L. Baughman

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DIAGENESIS AND RESERVOIR QUALITY OF THE EOLIAN NUGGET / NAVAJO SANDSTONE (EARLY JURASSIC), UTAH AND WYOMING

Laura I. Net, MSGeoSci

The University of Texas at Austin, 2003

Supervisor: Earle F. McBride

183 pages, 100 references, CD-Rom

The main diagenetic processes that affect the quality of the Nugget and Navajo Sandstone as hydrocarbon reservoirs are analyzed and quantified. During the Early Jurassic these two units were part of the largest known ancient dune field. The sandstones were subjected to different degrees of deformation and burial during the Late Cretaceous Sevier Orogeny.

The dataset comprises 100 samples taken from cores of two wells in the Anschutz Ranch East field (12,000 to 13,800 ft depth), and ten outcrop localities widespread in Utah and Wyoming. Four sandstone lithofacies were recognized based on field information and depositional characteristics such as texture, sorting, packing, and presence of laminations: avalanche (A), grainfall (G), ripple (R) and deformed (D) strata. Petrographic and petrophysical data reveal that, at a local scale, the environment (dune vs. interdune) and the mechanism of eolian transport and deposition determined the particular diagenetic pattern that would control porosity and permeability. The lithofacies show a positive correlation of porosity and permeability across the subsurface sample set (18% to 1%, and 70 md to 0.02 md, respectively). Petrophysical parameters (and thus reservoir quality) clearly decrease from avalanche, grainfall, ripples to deformed strata: avalanche layers are characterized by having the highest values of porosity and permeability, whereas deformed strata have very poor to no reservoir capability.

Sandstone architecture (average F71M2C19P8) and framework grain composition (average Q83F13R4) reflect the initial dominance of rigid grains (mostly monocrystalline quartz and subordinate K-feldspar) as well as the low matrix content that played major roles during compaction and cementation evolution. Depositional porosities and cement distribution are strongly controlled by lithofacies. The main diagenetic events affecting reservoir quality of these sandstones include mechanical compaction, quartz cementation, and clay authigenesis; secondary microporosity caused by dissolution of feldspars and rock fragments did not contribute significantly to fluid flow.

Continuous coats of authigenic pore-bridging illite effectively inhibited quartz cementation and account for the best reservoir quality characteristics observed in avalanche (A) strata. In contrast, irregularly distributed, early infiltrated detrital clay coats were less effective in retarding quartz overgrowths in grainfall (G) and wind-rippled (R) beds. Authigenic carbonates are not abundant in subsurface sandstones; in deformed strata, early pervasive carbonate cements do create barriers to fluid flow as do carbonate-cemented interdune deposits (C).

A regional analysis of the mechanisms of porosity loss in these sandstones indicates that shallowly-buried and weakly-deformed sandstones retain more than 15% original porosity in contrast with deeply buried sandstones from the fold-thrust belt, where more intense compaction reduced porosity to less than 15%. Compaction-to-cementation ratios indicate that best reservoir sandstones are relatively undercompacted (rather than undercemented) with respect to their tighter counterparts. Quartz cementation is closely tied to burial temperatures and ranges from tiny individual overgrowths in shallowly buried localities to pervasive pore-filling cement in the high-temperature, deeply buried sandstones of the fold-thrust belt. Areal distribution of quartz cement does not show a direct relationship to tectonic deformation, probably due to the local and variable influence of clay coats and texture at the lithofacies scale.

Core porosity and permeability values were successfully modeled using TouchstoneTM (91% and 94% of samples falling within tolerance envelops, respectively). Good reproducibility suggests that petrophysical parameters obtained from optimization runs can potentially be used to predict reservoir quality in frontier areas with sandstones of similar characteristics.


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LATE QUATERNARY GEOLOGIC HISTORY OF NEW JERSEY OUTER CONTINENTAL SHELF

Sylvia Nordfjord, PhD

The University of Texas at Austin, 2005

Supervisor: James A. Austin, Jr.

Analysis of high-resolution (1-4 kHz) seismic chirp profiles of the New Jersey mid-outer continental shelf, coupled with sediment samples, reveal the stratigraphic architecture resulting from the last glacio-eustatic cycle: dendritic (fluvial?) channel systems truncated by a transgressive ravinement. Quantitative geomorphologic analysis of these systems provides estimates of paleo-hydrologic parameters needed to link channel morphology to the hydrodynamic setting when these systems were active. These channels were presumably fluvial systems developed on a subaerial shelf during the Last Glacial Maximum (LGM), ~22-20 ka. During ensuing Holocene sea-level rise, these fluvial channels became estuarine/tidal, before erosion and final burial. Mean tidal paleo-flow estimates for these systems with flow velocities of 1.0-1.5 m/s and shear stresses sufficient to initiate transport of grains 2-8 mm in diameter (i.e., coarse sand and fine gravel) as bed-load, are consistent with modern tidal creeks of the same dimensions. However, paleo-flow estimates, assuming a fluvial environment with velocities of 1.1-2.0 m/s, and retrodicted fluvial discharge and boundary shear stresses would have been sufficient to transport particles up to ~15 mm in diameter (i.e., gravel) as bed-load. We suggest that either the fluvial drainages never reached equilibrium during high-discharge flows, perhaps due to melt-water pulses following the LGM, or that tidal influences have modified the original fluvial geometry. Imaged and sampled channel-fills reveal a retrogradational shift of four sedimentary facies, in ascending order: 1) fluvial lags, SF1, 2) estuarine mixed sand and muds, SF2, (3) estuary central bay muds, SF3, and 4) redistributed estuary mouth sands, SF4. Three intra-fill transgressive surfaces, B1-3, interpreted as bay flooding surface, intermediate flooding surface and tidal ravinement, respectively, are also either wholly or partly preserved. Our study demonstrates that wave- and tide- dominated facies can coexist within channel fills. These fill units are truncated by a morphologic irregular, transgressive wave ravinement surface, the T-horizon, which, in turn, is overlain by Holocene marine sand deposits. A ~10 m bathymetric rise in T forms both the mid-shelf scarp and the base of a smaller Holocene wedge. The modern seafloor of the New Jersey shelf experiences post-transgressive erosion, which is variously expressed.


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FRACTURE-SIZE SCALING AND STRATIGRAPHIC CONTROLS ON FRACTURE INTENSITY

 Orlando José Ortega Pérez, Ph.D.

The University of Texas at Austin, 2002

Supervisor: Randall A. Marrett

Scaling techniques offer an opportunity to solve subsurface fracture-sampling problems by extrapolating fracture properties from sub-millimeter-scales to scales important for economic applications. Although extrapolation of fracture length and aperture distributions across observation scales is fraught with potential errors, sampling of opening-mode kinematic apertures along scanlines using new fracture-aperture measuring tools produces consistent power-law aperture distributions from the micron-scale to outcrop-scale. One-dimensional sampling avoids fracture connectivity issues inherent to traditional two-dimensional length sampling methods. Sampling artifacts and mechanical layer effects can be diagnosed and accounted for, and extrapolation of power-law fracture intensities from the sub-millimeter scale up to the length scale of mechanical layers is feasible. Tests were performed in turbidite beds of the Ozona Sandstone, Texas, eolian Weber Formation sandstones, Colorado, and Lower Cretaceous carbonates of the Sierra Madre Oriental (SMO), Mexico.

Outcrop studies in Weber Formation sandstones provided an opportunity to characterize well-exposed macrofracture systems as potential analogues for subsurface fractured reservoirs at Rangely Field. However, differences in stratigraphy and diagenetic history between surface and subsurface do not allow the direct extrapolation of these results to subsurface, reinforcing the idea that local data are necessary for fracture system characterization even in cases where long geologic time has passed between the time of sedimentation and the time of deformation that brought potential outcrop analogs to the surface.

Another way to predict fracture properties in the subsurface is to analyze the relationships between fracture attributes and the geologic parameters of the rock volume that govern fracturing. Fracture-fill prediction using relative volumes of cement phases precipitated during and after fracture timing shows an empirical relationship with sedimentary facies in Weber Formation sandstones. Multivariate analysis of unbiased fracture intensity in SMO carbonates suggests that degree of dolomitization and position of a bed at the top of a stratigraphic cycle are the most important controls on fracture intensity in these rocks. Mud content has only a modest control on fracture intensity and bed thickness has the least control on fracture intensity, suggesting that published work concluding that fracture intensity is strongly governed by bed thickness may be biased by scale or sampling effects.

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DELTAIC TO ESTUARINE REGIME CHANGE ON THE PROXIMAL PALEO-ORINOCO SHELF, MORNE L'ENFER FORMATION, TRINIDAD

Ariana Osman, MSGeoSci

The University of Texas at Austin , 2006

Supervisors: Ron J. Steel and Lesli Wood

The Morne L'Enfer Formation, onshore southern Trinidad, records the regressive-to-transgressive shelf transit of the Late Pliocene Orinoco delta as it built across south Trinidad . Much of our current understanding of paleo-Orinoco sand reservoirs come from the storm-wave dominated outer-shelf and shelf-edge areas in the Columbus Basin . The Morne L'Enfer Formation, however, encapsulates an early regressive deltaic phase of a wave-tide-dominated delta, the sequence boundary and the turnaround to a tide-dominated estuarine phase in the proximal paleo-Orinoco.

Integration of outcrop and well data provides a window into better understanding the delta-estuary cycle at an inner-shelf site, illustrating how the regime change on deltas lead to contrasting style of tide-dominated reservoir facies and architectures.

The basal regressive deltaic deposits show repeated coarsening upward parasequences, up to 25m thick . These sand packages have a very heterolithic character suggesting a mixed wave-and-tide influenced, rather than wave-dominated regime .

The overlying transgressive deposits are characterized by thick channelized units of blocky coarse-grained sands, ranging from 25 – 50m thick . The clean-water, tidal character of the environment is evident in outcrop by (1) repeated sandprone units with stacked of 2-D dunes, some flood oriented, (2) sigmoidally cross stratified sands and (3) rhythmic sand and mud stratal units. The thickness and blocky but dis-connected nature of the tidal-channel sands suggests that the earlier distributary valleys became a back-filled, sandy estuarine system, providing better hydrocarbon reservoir than the related, underlying regressive deltaic half-cycle.

The character of these proximal delta-estuary couplets, compared with those developed at the shelf edge, provide data for a proximal-distal regime change model on the paleo-Orinoco shelf, and for the contrasting reservoir geometry between regressive and transgressive phases of shelf cycles.

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DIAGENESIS AND POROSITY EVOLUTION OF THE FLATHEAD SANDSTONE (MIDDLE CAMBRIAN), WYOMING, AND MONTANA

Aysen Ozkan, MS.

The University of Texas at Austin, 2001


Supervisor: Earle F. McBride

The Flathead Sandstone is a shallow marine sandstone deposited during middle Cambrian transgression on the Precambrian basement rocks over much of Wyoming and southern Montana. The Flathead is composed of coarse to medium grained sandstones. Conglomerate layers are present close to the base. Shale layers are scattered through formation and more common in the upper part.

Polycrystalline quartz types, feldspars, biotite, metamorphic and granitic rock fragments, and absence of chert indicate that underlying crystalline rocks and similar rocks outside the basin of deposition were the major source rocks.

Composition ranges from quartzarenite to arkose (average Q92F7.4R0.6). Reconstructed composition indicates loss of 1.8 to 2.7% (whole rock) of the original feldspars.
The Flathead has undergone physical and chemical compaction, recrystallization, dissolution, oxidation, reduction, grain fracturing, and generation of different authigenic cements and replacement minerals in the course of burial to from 5 to 7 km. Quartz, Fe-oxide, kaolinite, calcite, siderite, ankerite, dolomite, chalcedony, and opal are present as cement in the Flathead (in decreasing order of abundance). Also trace amounts of K-feldspar, pyrite, Ti-oxide (anatase/brookite?), barite, and tourmaline are present.

According to fluid inclusion data from Teton Pass locality minimum estimate of Tmax (maximum formation temperature) reached is 150-160°C. Silica for the quartz cement was derived mainly from intergranular pressure solution, and stylolites, and also dissolution of silicate framework grains. Some silica may have been derived from S/I transformation within the shale layers, and overlying formation.

Oxygen and carbon stable isotope data, microprobe data, textural, and CL studies indicate that calcite and dolomite cement formed during deep burial, but later were recrystallized in meteoric water. The source of carbon for carbonate cement is mainly biogenic carbonate.

Total porosity ranges from absent to 11.5% and averages 3.6%. Secondary porosity, which is generated by dissolution of unstable framework grains (especially feldspars), and carbonate cement, makes about 1.5% of the total porosity. Calculations indicate that compaction was more important than cementation in reducing the porosity of the sands. Permeability ranges from 0.5 to 439 mD, with a geometric mean of 5.8 mD. In general permeability increases with increasing porosity.

This study involves a petrographic and diagenetic study of the Flathead Sandstone in Wyoming and south-central Montana. The purposes of the study are to evaluate the lateral and vertical variations in mineralogy, porosity, and permeability; to reconstruct the diagenetic evolution of sandstones; to determine the control of diagenesis, tectonic setting, depositional environment and source rocks on resulting composition, and to determine the provenance of the sandstones.

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THRUST FAULT CHARACTERISTICS INFERRED FROM 3D SEISMIC REFLECTION DATA FROM THE NANKAI TROUGH SUBDUCTION ZONE, SOUTHWEST JAPAN

Emily Marleah Pangborn, MSGeoSci

The University of Texas at Austin, 2007

Supervisors: Nathan L. B. Bangs and Robert H. Tatham

The study of fault properties within the Nankai Trough subduction zone is of interest due to the periodic occurrence of highly destructive earthquakes and tsunamis in this region. Therefore, for better understanding of the seismogenic and tsunamigenic potential of faults within the accretionary prism, my research focuses on characterizing fault geometry and seismic reflectivity in the major splay fault system based on observations from 3D seismic reflection data. My observations suggest that faulting within the splay fault system is evolving in the landward direction and that fluid migration may be occurring along some of the most recently active faults in the splay system. In addition, modeling results indicate that a strong negative-polarity fault-plane reflection in the splay fault system is caused by a thin layer of low acoustic impedance material, which could be representative of a major fluid conduit.

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PETROGRAPHIC CHARACTERIZATION OF THE BARNETT SHALE, FORT WORTH BASIN, TEXAS

Petros Konstantinos Papazis, M.S. Geo. Sci.

The University of Texas at Austin, 2005

Supervisor: Kitty L. Milliken

Shale sedimentology is one of the less explored areas of sedimentary geology. Shales account for two-thirds of the sedimentary rock record and preserve large portions of Earth’s history in relatively continuous successions. In addition, these rocks serve as a key element of basin-scale fluid flow systems and are the primary source of materials released from water-rock interactions at depth. The Mississippian Barnett Shale of north-central Texas is of particular interest because it serves as both source rock and hydrocarbon reservoir for the Newark East Field, the largest gas field in Texas (Montgomery et al., 2005), and the target of intense current exploration interest.

This study explores the petrographic characterization of the Barnett Shale by identifying the different silt-, sand-, and granule-size grain types; quantifying percentages and ratios of clay-size to silt-, sand-, and granule-size grain fractions; and determining the nature of the clay-size constituents. Samples used in this study come from four cores in Cooke, Erath, and Wise counties in north-central Texas, and from outcrop in Lampasas and San Saba counties in central Texas. An integrated approach utilizing transmitted polarized light microscopy, secondary and back-scattered electron imaging, cathodoluminescence imaging, X-ray mapping, and X-ray diffraction is applied to 76 polished thin sections.

Five major lithologic groups are identified from core observations: 1) black shale relatively lacking in silt-size particles; 2) calcite-rich lithologies; 3) silt-rich black shale; 4) coarse grain accumulations that include calcite-rich and phosphate-rich varieties; and 5) concretions. Grain types for each lithology are classified based on their provenance, as either extrabasinal or intrabasinal particles. Extrabasinal particles include plant fragments and detrital silt-size quartz, feldspar, and mica. Intrabasinal particles are subdivided into calcareous and non-calcareous fossils, coated grains, and phosphatic intraclasts. Authigenic phases identified include Ca-phosphate, calcite, dolomite, ankerite, pyrite, quartz, albite (?), chlorite, barite, sphalerite, P-rich moganite, and titanium-oxide. The results of this study reveal that clay minerals are not the dominant components in these rocks, which are dominated instead by silt- and clay-size quartz, and locally, by biogenic debris and phosphatic intraclasts.

This research demonstrates that the Barnett contains a rich variety of lithologies that denote important environmental variations. Ultimately, documentation of the spatial distribution of these lithologic types can contribute to a regional environmental/stratigraphic model that can then be further linked to mechanical properties within this important economic unit. An understanding of rock properties in the Barnett has wide-ranging implications because this little-understood rock type forms fractured-shale gas systems worldwide.


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OXYGEN ISOTOPE VARIABILITY IN CENTRAL TEXAS PRECIPITATION, CAVE DRIP-WATER, AND TRAVERTINE CALCITE

James Russell Pape, B.S.

The University of Texas at Austin, 2008

Supervisor: Jay Banner

This study investigates the factors that control the oxygen isotope composition of precipitation and cave drip-waters in central Texas. Cumulative precipitation samples collected in Austin, Texas at monthly to bimonthly intervals between 1999 and 2007 have d18O values between -12.5 and -1.1‰ VSMOW. This study finds that source region plays an important role in determining the oxygen isotope composition of precipitation for individual storms. Precipitation from moisture of a Pacific Ocean origin has highly depleted oxygen isotope compositions compared to average precipitation originating from the Gulf of Mexico. However, precipitation from hurricanes from the Gulf of Mexico can also have very low d18O values comparable to precipitation of a Pacific Ocean origin. Rainfall amount is an important control on the oxygen isotope composition of rainfall during the warmest periods. However, neither ambient surface temperature nor rainfall amount can completely explain the variability of the oxygen isotope composition of precipitation in the entire dataset.

Drip-water samples collected at monthly to quarterly intervals from multiple drip sites in three central Texas show caves between 1998 and 2007 have d18O values between -5.5 and -0.1 ‰. Cave drip-waters have significantly less oxygen isotope variability than Austin rainfall, generally varying by no more than l‰ of their average values. Cave drip-waters generally plot near the Local Meteoric Water Line and have d18O values that are close to the weighted average of local precipitation on an annual or greater scale. This indicates that the oxygen isotope composition of local precipitation above the caves is the primary influence on the oxygen isotope composition of cave drip-water. Mixing of meteoric waters in the unsaturated zone above the caves can account for the lack of variability in cave drip-water oxygen isotope compositions. Average values of cave drip-waters display a continental effect in which drip-water d18O values become lower moving further inland from the Gulf of Mexico. This likely reflects a similar continental effect on precipitation above the caves. Temperature and elevation gradients may also contribute to this continental effect. The results of this study have implications for speleothem paleoclimate records. Speleothem oxygen isotope records from these caves would likely reflect long term climate variations and may be useful in determining the moisture source region of past precipitation.

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SEISMIC LITHOLOGY AND DEPOSITIONAL FACIES ARCHITECTURE IN THE TEXAS GULF COAST BASIN: A LINK BETWEEN ROCK AND SEISMIC

Yong-Joon Park, Ph.D.

The University of Texas at Austin, 2003

Supervisor: William L. Fisher
233 pages, 89 references, color figures

Amplitude variation with offset (AVO) is a seismic attribute containing valuable lithology information. Although AVO analysis can provide three-dimensional lithology information, the technique has not been sufficiently utilized in many geologic interpretations owing to the difficulty in handling pre-stack seismic data. Moreover, most previous AVO analyses have solely focused on detecting gas sands. This study suggests a convenient method to extract a seismic lithology attribute using an AVO crossplot method.

A crucial step for AVO analysis is to understand relationships between AVO attributes and rock properties. Missing petrophysical data can be estimated by proper empirical relationships. However, a uniform rock property assumption disregarding lithology variation has to be avoided in order to predict an accurate AVO response. Synthetic seismic modeling enables us to predict AVO crossplot responses depending on variations in each rock property. A change in the Vp/Vs or Poisson's ratio affects the slope of the AVO crossplot trend. A change in the impedance contrast across the interface causes rotation and scattering of AVO crossplot points. An AVO crossplot of actual seismic data qualitatively coincides with the synthetic modeling result based on the mixed lithology assumption. A seismic lithology attribute cube is created by muting the unimportant lithology AVO crossplot trend and highlighting the preferred lithology crossplot trend.

Based on the seismic lithology attribute, this study attempted to interpret depositional facies. Depositional features are easily recognized on seismic horizon slices. Combining seismic lithology and proportional horizon slicing methods enhances interpreting depositional facies architecture and stratigraphic sequence. Seismic lithology is especially useful for interpreting the depositional facies that do not have distinct channelized features. Various shorezone depositional facies are recognized including shoreface sheet sand, barrier bar, lagoonal delta, and muddy facies. Moreover, high-frequency stratigraphic sequences are identified by seismic lithology maps by interpreting successive horizon slices.



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MAGMATIC AND PERVASIVE HYDROTHERMAL MINERALOGY OF THE GRASBERG CU-AU PORPHYRY COPPER DEPOSIT (WEST NEW GUINEA)

John Terrill Paterson, M.S. Geo. Sci

The University of Texas at Austin, 2004

Supervisor: Mark Cloos

332 pages, 87 references

Chapter 1: Magmatic Mineralogy of the Grasberg Igneous Complex

The Grasberg Igneous Complex is host to one of the largest copper porphyry systems, currently producing 6 % of the world's copper supply. This study focuses on the spatial distribution of magmatic characteristics throughout the three main phases of intrusion: the Dalam, subdivided into the Dalam Andesite, Dalam Volcanic and Dalam Fragmental, the Main Grasberg Intrusion (MGI), and the Kali (Early and Late). A sample suite from the open pit mine included 225 polished slabs and thin sections. Variable hydrothermal alteration overprints and locally completely replaces magmatic mineralogies. All three units contain magmatic plagioclase and biotite as the overwhelmingly dominant phenocryst phases. The Dalam Andesite, MGI and Late Kali contain(ed) magmatic hornblende as well. Both the Kali and the MGI contained minor (< ~5 %) amounts of magmatic clinopyroxene in addition. Apatite, found in all units, is the most abundant trace (< 1 %) phase. Magmatic magnetite is present in the Kali. Analysis of the sample suite reveals no examples of material from the surrounding country rock as clasts in the igneous units. The presence of abundant broken phenocrysts in the Dalam phase rocks suggests that some form of auto-fragmentation occurred during emplacement.

Reconnaissance microprobe analyses on the main phenocryst phases (plagioclase, biotite and amphibole) reveal no systematic variation in the chemistry of the phases. Microprobe mapping indicates the magmatic groundmass in the Kali was potassium feldspar, albitic plagioclase, quartz and biotite. A similar assemblage probably existed in the MGI and Dalam phase rocks, but overprinting hydrothermal alteration prevents confirmation.

Texturally, the units are distinct with the porphyritic Dalam Andesite, brecciated Dalam Volcanic and Dalam Fragmental units, comparatively equigranular MGI and porphyritic Kali. The Dalam phase rocks were emplaced as a near-surface intrusion that became volatile-saturated while erupting (forming the Dalam Fragmental) while concurrent eruptive activity formed the polymict Dalam Volcanic. The MGI and the two-phase Kali were passively emplaced. The MGI intruded the still hot core of the Dalam. The volumetrically minor Early Kali appears to be a plug into the center of the MGI whereas the Late Kali is a large wedge-shaped dike.

Chapter 2: Pervasive Hydrothermal Mineralogy of the Grasberg Igneous Complex

Much of the rock volume in the Grasberg Igneous Complex (GIC) has been altered by hydrothermal fluids. In parts of the Dalam Volcanic and Dalam Fragmental units, the alteration is severe enough to destroy all magmatic phases within a hand sample. Nearly all of this alteration is the manifestation of hot magmatic fluids pervasively infiltrating the groundmass of the rock volume. Petrography reveals that three simple zones within the GIC characterize the volumetrically predominate minerals. The 1 km-wide core of the deposit is dominated by biotite + magnetite with an inner ~ 500 m-wide zone of andalusite, whereas the exterior annular region, ~ 500 m across, is dominated by sericite + anhydrite + pyrite with small amounts of kaolinite in some samples. Pockets of epidote with minor chlorite are present in the distal portions of the GIC. Overprinting relationships are spatially limited relative to other deposits. For example, the overprint of sericite + anhydrite + pyrite upon biotite + magnetite is less than 150 m wide at its most extensive, suggesting the boundaries between these two mineralogic zones were comparatively sharply defined. The limited extent of this overprint indicates an abrupt shutdown of the pervasive infiltration of magmatic fluid. Microprobe analyses of hydrothermal biotites indicate that they record equilibration with only slightly cooler, hydrothermal fluids relative to the temperatures of magmatic crystallization.

The abundances of hydrothermal minerals indicate that extensive hydrothermal alteration post-dated the intrusion of the Main Grasberg Intrusion and predated the intrusion of the Late Kali (LKI). The Early Kali Intrusion postdated all but the last portion of hydrothermal alteration. The simple hydrothermal mineralogy is explicable by a simple model of acid-production and consumption in which the central core of the GIC produces acid primarily by precipitating abundant magnetite while the exterior of the GIC consumes acid by hydrolysis of silicates, resulting in the crystallization of sericite and texturally destructive alteration. Hydrolysis of SO2 generated H2S and H2SO4 that resulted in sulfide mineral and anhydrite precipitation. The mineralogic zonation reflects the thermal structure of the GIC.

The alteration mineralogy resulting from pervasive fluid flow in the Grasberg Igneous Complex is simply categorized into a central biotite + magnetite zone with an inner biotite + magnetite + andalusite subzone, a peripheral zone of sericite + anhydrite + pyrite with a minor overprint of kaolinite. The progression of silicate hydrothermal minerals is represented in the simple system K-AI-Si-O-H, and modeled to describe the evolution of the pervasively infiltrating hydrothermal fluid. Calculations of phase stability dependent upon pressure, temperature and the log (aK+/aH+) ratio in the fluid explain the major variations in hydrothermal mineralogy.

Therein, changes in the acidity of the hydrothermal fluid are directly reflected by hydrothermal phase stability. The occurrence of andalusite in the core of the GIC coupled to the predominance of sericite in the exterior of the deposit requires two fluid pathways: 1) a quasi-isothermal flow path coupled to an increase in acidity, stabilizing andalusite, and, 2) a cooling path also coupled to an increase in acidity. These two paths explain the volumetric majority of hydrothermal minerals within the Grasberg system. Different paths are the consequence of a pressure gradient in the hydrothermal fluids, from lithostatic values near the magmatic cupola to hydrostatic values near the surface. This gradient drives the fluids upwards as well as outwards.

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GEOCHEMICAL AND ISOTOPIC TRACING OF PALEOZOIC GROUNDWATER FLOW IN BREACHED ANTICLINES: A CASE STUDY AT LOWER KANE CAVE, BIGHORN BASIN, WYOMING

Melissa Edwards Pearson, M.S.Geo.Sci.

The University of Texas at Austin, 2004

Supervisor: Philip C. Bennett

Lower Kane Cave is forming in the upper Mississippian Madison Limestone by sulfuric acid speleogenesis. The cave is located along the axial trace of the Little Sheep Mountain anticline where the Paleozoic units have been exposed in a canyon cut by the Bighorn River. The Madison Limestone comprises the upper section of the Madison aquifer, which serves as an important regional aquifer for water supply and petroleum production in much of Wyoming, Montana and the Dakotas. Compared to other Madison springs and wells in the region, the cave springs are characterized by a higher concentration of TDS, SO 4 and H 2S, differences which likely contribute to the localization of cave formation. This study used geochemical and strontium isotope data to determine signatures for the Madison aquifer and other Paleozoic aquifers of the Bighorn Basin to constrain the origin of groundwater to Lower Kane Cave.

Mississippian Madison aquifer waters are characterized by lower [Sr] and higher 87Sr/ 86Sr (between 0.70891 – 0.70925), than groundwater in the overlying Pennsylvanian Amsden and Tensleep and Permian Phosphoria aquifers, which have 87Sr/ 86Sr values between 0.70789 – 0.70856. These values are slightly greater than established marine values of 87Sr/ 86Sr for the respective depositional periods. Coupled with the increased concentrations of TDS, SO 4 and H 2S, the distinctly radiogenic 87Sr/ 86Sr ratios of 0.71001 to 0.71012 measured at the cave springs suggest that the springs of Lower Kane Cave are the result of mixing between Madison waters and a thermal, saline, radiogenic endmember. Data from the Thermopolis Hot Springs in the southern Bighorn Basin support the existence of such a water within the lower Paleozoic section in the Bighorn Basin of Wyoming, suggesting that similar flow systems operate at the Thermopolis and Little Sheep Mountain anticlines, and potentially at Sheep Mountain anticline as well. These results further demonstrate the importance of structural controls on groundwater flow in the Bighorn Basin, and have implications for our understanding of cave localization and fracture controlled flow at anticlines within the Bighorn Basin, as well as at similar zones of foreland compression in other areas.


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STRUCTURAL ANALYSIS OF THE PICKETT PEAK TERRANE NEAR THE COAST RANGE FAULT AND ITS TECTONIC IMPLICATIONS, EASTERN FRANCISCAN BELT, NORTHERN CALIFORNIA

John Joseph Perri, M.S. Geo. Sci.

The University of Texas at Austin, 2005

Supervisor: Mark Cloos

High-pressure coherent blueschist terranes of the Eastern Belt of the Franciscan Subduction Complex in the Coast Ranges of northern California are juxtaposed against the low-pressure Great Valley Group rocks of the Sacramento Valley, resulting in a major tectonic discontinuity. The Pickett Peak terrane of the Eastern Franciscan Belt is comprised of the South Fork Mountain Schist and the structurally underlying Valentine Spring Formation. Both are lawsonite + aragonite-bearing blueschist facies metasediments with minor metavolcanics that reached depths of 20-25 km and temperatures of 250-350°C during Mesozoic-Cenozoic subduction of the Farallon Plate beneath North America. The high-angle Coast Range Fault separates the Franciscan Complex, the remnants of an accretionary prism, from the unsubducted rock of the Coast Range Ophiolite and overlying forearc basin deposits of the Great Valley Group. The ≥ 10 km of relative uplift required across the Coast Range Fault has been well constrained by petrologic studies; few structural studies have been performed to provide kinematic constraints on uplift mechanisms.

Ar-metamorphic ages indicate peak temperatures in the Pickett Peak terrane were attained at 110-150 Ma. Fission track data indicate cooling to ~110°C at ~60 Ma, corresponding to a depth of ~10 km. The oldest rocks containing significant amounts of surficial reworked coherent blueschist sediments are Miocene in age. These constraints, combined with the lack of a greenschist facies overprint and the presence of aragonite, indicate slow synsubduction uplift of the Pickett Peak terrane.

A total of 2 km of excellent roadcut exposures were studied along Forest Highway 7 between Elk Creek and Alder Springs within the Mendocino National Forest. The orientations of 2374 metamorphic foliations, 629 fold axes, and 89 fault planes, as well as kinematic indicators of fault block motion, were collected at 17 roadcuts, all but one of which are within the South Fork Mountain Schist. Eleven of the roadcuts are within a few hundred meters of the Coast Range Fault; the remaining six roadcuts are progressively farther from the fault.

The compositional layering-parallel penetrative cleavage at roadcuts close to the Coast Range Fault is subvertical, dipping steeply SE or NW. ~1 km away from the fault, the cleavage forms 100 m-scale asymmetric chevron folds with longer SE-dipping limbs and shorter NW-dipping limbs. At distances greater than 1 km from the fault, the cleavage is gently undulating. Cm- to m-scale folds at all roadcuts are minor structures that are too small to be represented by the scale at which foliation measurements were taken. Faults do not have a preferred attitude or sense of displacement. Although they are prevalent (one fault per ~20 m), they are considered to have been uninvolved in the uplift of the Pickett Peak terrane.

The structural data presented here, combined with previous petrologic, detrital, and fission track studies, are used to make a tectonic model to account for the uplift of this coherent blueschist terrane. Sediments that would become the Pickett Peak terrane were deposited on the downgoing Farallon Plate and subducted to 20-25 km depth in the Late Jurassic-Early Cretaceous. Dewatering of the upper part of subducting sediments caused them to decouple from the descending plate and underplate to the bottom of the hanging wall. Rocks of the South Fork Mountain Schist were some of the first to accrete and experienced the highest peak temperatures. Rocks of the Valentine Spring Formation accreted under the schist and were subjected to slightly higher pressures but lower temperatures. Folding and faulting were coeval and postdate peak temperatures, indicated by the lack of axial planar cleavage. Continued underplating at a rate of ~150 m/m.y. and normal motion along the Coast Range Fault, combined with an unroofing process, had brought blueschists to within a few km of the surface when subduction ended. Postsubduction lithospheric removal resulted in buoyant uplift of the Coast Ranges and widespread exposure of Franciscan blueschists in most of California.



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FIELD AND PETROGRAPHIC ANALYSIS OF MYLONITIC FABRICS: IMPLICATIONS FOR TECTONIC CORRUGATION DEVELOPMENT, TANQUE VERDE RIDGE, ARIZONA, USA

Ethan Richard Perry, M.S. Geo. Sci.

The University of Texas at Austin, 2005

Supervisor: Sharon Mosher

Tanque Verde Ridge (TVR) in Saguaro National Park, Arizona, USA, represents a large-scale lineation-parallel ridge (tectonic corrugation) within the Santa Catalina-Rincon Core Complex. Field and petrographic features record a history of lineation-parallel extension and boudinage occurring across a ductile to brittle deformational continuum during core complex exhumation. Lineation-perpendicular ductile to brittle features suggest the importance of extension orthogonal to lineations during exhumation and need to be factored into the debate on tectonic corrugation evolution.

TVR is a foliation-defined antiformal flexure, concordantly bounded at the toe by a brittle detachment fault system. The footwall mylonite is strongly foliated (suggestive of flattening, rather than constriction) and lineated (WSW-trending). Ductile, micro- (thin section) to macro- (hundreds of meters) scale features are oriented both lineation-parallel (e.g., S-C’ fabrics, asymmetric porphyroclasts, shear zones) and perpendicular (e.g., shear zones, asymmetric quartz fabrics). These features record dominantly WSW, and secondarily NNW and SSE, directed non-coaxial shear, respectively. Across the corrugation, foliation flexures exhibit both lineation-parallel and perpendicular fold axes. Distended necks of micro- to meso-scale boudins contain NNW-SSE striking zones of intense brittle fracturing, brecciation and cataclasis. The ductile, mylonitic foliation is passively affected across these boudin neck zones as foliation dip varies from sub-horizontal to >45°. This suggests a temporal link between mylonite formation, extension-related deformation and the development of the corrugated surface.

Oriented thin sections and field observations from across TVR and across outcrop-scale corrugation-like features constrain the conditions during mylonite development to lower-amphibolite facies and the spatial relationship of micro- to meso-structural features across the corrugation. On the basis of field and petrographic evidence, a new model for the evolution of tectonic corrugations is proposed, whereby original anastamozing shear zones within the deep-seated, ductile shear zone are amplified in response to bidirectional extension (including boudinage, and spatially related brittle fracturing). Shear zone modification is progressive and is synchronous with non-coaxial simple shear. Overall flattening of the shear zone is predicted in response to this extension. Notably, mylonitic fabrics at TVR do not record a history of large-scale constrictional deformation. Tectonic corrugations can initiate at depth as a result of original shear zone morphologies, be modified by boudinage during bidirectional extension, and be translated up-dip during progressive core complex exhumation. Corrugations are manifestations of deep-seated, multi-scale processes that influence shear zone dynamics during large-scale crustal extension.

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THE ENVIRONMENTAL IMPACT OF CLASS A FIREFIGHTING FOAM

Jennifer Leigh Perry, M.S. Geo. Sci.

The University of Texas at Austin, 2001

Supervisor: Philip C. Bennett

Class A foam is widely used in wildland and structural firefighting as an extinguishing agent. Commonly, Class A foam concentrate consists of a mixture of water, glycol, and a blend of surfactants to enhance the 'wetting' capability of water. Class A foam is attractive to fire fighters as it enhances heat absorption of water, while increasing fuel moisture content, resulting in more effective extinguishment with less water, and greater safety. In other settings, however, surfactants change soil properties, alter infiltration rates, and enhance contaminant mobility. Evaluation of wildfires at Los Alamos National Laboratory raised the question of the impact of extinguishing agents on the mobility of high explosive residues, such as 2,4,6-trinitrotoluene (TNT), in soil. Additionally, combustion of wood and other organics can produce polycyclic aromatic hydrocarbons (PAHs), such as naphthalene, which have been identified by the US Environmental Protection Agency as priority pollutants. The use of agents such as Class A foam may enhance the solubility and transport of such hydrophobic compounds, flushing residues out of soil and into underlying water bearing units.

Field and laboratory experiments were performed to evaluate the potential impact of Class A foam on the solubility and transport of organic contaminants in soil. The persistence of Class A foam under non-fire, wildfire and pre-burn versus post-burn application conditions was analyzed. Solubility of TNT and naphthalene in 0.1, 0.5 and 3% Class A foam solutions was determined. Alteration of transport characteristic for these two compounds was investigated using laboratory column experiments.
Field investigations show that Class A foam applied at recommended concentrations (<0.5%) persist in soil for about three weeks. Actual application rates are as much as ten TimesNewRoman the recommended rate due to equipment variability and/or repeated application during actual fire situations, and here surfactants persist for more than two months. Foam persistence decreases after exposure to fire, suggesting that surfactants volatilize or decompose during the fire.

Foam solutions at typical application mixtures have a significant effect on the solubility of hydrophobic soil contaminants. TNT solubility increased 20% and naphthalene increased 300% in a 3% foam solution, suggesting that above the critical micelle concentration, foam solubilizes these contaminants. Low concentrations of foam decreased the solubility of naphthalene by 50% and increased retardation, while it enhanced the transport of TNT.

While Class A foam offers clear advantages for fire suppression, the use of high foam concentrations carries with it environmental consequences. By increasing the solubility of organic contaminants at high foam concentrations, surfactants may increase the mobility of polar organic contaminants in soil into sensitive aquifers or surface water supplies. Additionally, fire managers should be aware of the effects of foam applications above manufacturer's recommended guidelines.

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HYPERPYCNAL FLOW VARIABILITY AND SLOPE ORGANIZATION OF AN EOCENE SHELF MARGIN, CENTRAL BASIN, SPITSBERGEN

Andrew Lucas Petter, MSGeoSci

The University of Texas at Austin, 2005

Supervisor: Ronald J. Steel

Identification of bypass at the shelf margin is critical to deepwater exploration. The shelf margin of an early Eocene fourth-order sequence with an attached basin-floor fan in the Central Spitsbergen Basin was examined in this study. Turbidity currents were fed mainly by hyperpycnal flow emerging from shelf-edge deltas. The lifespan of any turbidity current was determined primarily by the sediment concentration of the flow and the duration of the river flood. High-density hyperpycnal flows created sand-filled slope-channel complexes 10-15 meters (33-49 feet) thick and 100-200 meters (328-656 feet) wide that served as conduits for bypass to the basin floor. Low-density hyperpycnal flows were unconfined and deposited heterolithic lobes on the slope. Shelf-margin accretion of ~1.5 kilometers (0.9 miles) during the falling stage gave way abruptly to bypass in the early lowstand. Most of the basin-floor fan growth was achieved after shelf-edge incision and before relative sea level rise. Coastal-plain aggradation in the late lowstand sequestered sediment from the shelf-edge distributaries, effectively diminishing high-density hyperpycnal output. The late lowstand was therefore marked by a second pulse of shelf-margin accretion with only limited bypass to the basin floor, and a heterolithic, prograding complex downlapped the early lowstand channels. Transgression ultimately led to abandonment of the shelf-edge delta complex and accumulation of mainly mudstone on the margin. The shelf-margin architecture exhibited in this sequence should serve as a type example of a deepwater feeder system in which hyperpycnal flow is the primary initiator of turbidity currents for sand accumulation on the slope and basin floor.

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Sequence Stratigraphic and Architectural Characterization of a Permian Carbonate Ramp, upper San Andres Formation, Last Chance Canyon , New Mexico

Ryan Matthew Phelps, M.S. GeoSci

The University of Texas at Austin , 2006

Supervisor: Charles Kerans

Characterizing stratal architectures of carbonate outer ramps is an essential part of understanding the depositional processes fundamental to carbonate systems. Accurate representation of the observed facies and stratal geometries requires extrapolation of data into three-dimensions. High resolution digital outcrop models allow the opportunity to interpret and represent outcrop-scale observations in three-dimensions with spatial accuracy. Examination and modeling of Permian (Guadalupian) mixed carbonate-siliciclastic stratigraphy in Last Chance Canyon, Guadalupe Mountains, New Mexico reveals distinct variability in stratal geometries from the ramp crest to distal outer ramp. In numerous places along the ramp profile, the Guadalupian-8 high frequency sequence of the upper San Andres Formation possesses significant mounded geometries that are the result of both constructional and erosional processes. In the fusulinid-rich outer ramp the geometries are the result of bioherm construction, fusulinid mound construction, and erosion by storm waves and currents. In the mud-dominated distal outer ramp the observed geometries are representative of a low-sinuosity carbonate channel-levee complex with grain-rich facies centered in channelized areas. This study chronicles the three-dimensional stratigraphic development of the outer ramp mounds and distal outer ramp channel-levee complex while placing them in a sequence stratigraphic context. Sequence stratigraphic interpretations of the carbonate ramp clinothems suggests that the mounded geometries and channel-levee complex formed during a transgressive sequence. The transgressive nature of the sequence allowed generation of significant quantities of carbonate mud for exportation to the levees and promoted growth of outer ramp mounds into unfilled accommodation. The onset of the subsequent highstand sequence led to siliciclastic sediment bypass into the basin, termination of mounded outer ramp geometries and ultimately resulted in transformation of the carbonate dominated ramp to a mixed carbonate-siliciclastic shelf.

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TRANSIENT MODELING OF CONTAMINANT TRANSPORT IN DUAL POROSITY MEDIA WITH FRACTURE SKINS

Thandar Phyu, M.S.

The University of Texas at Austin, 2002

Supervisor: John M. Sharp, Jr.

Fractures are ubiquitous in nature and can serve as preferential flow paths for solute transport especially in low permeability rocks. If fracture skins are present, they may have different hydrogeological properties than the unaltered rock and, therefore, may impact the hydraulic and transport properties of the media.

This study considers a finite-length system with set of equidistant parallel fractures having a uniform aperture and fracture skins of constant thickness. The operating processes include: advection and Taylor dispersion in the fracture; diffusion into the skin and matrix; and sorption to the fracture, skin, and matrix. For the model input, data from the Brushy Canyon Sandstone of West Texas are utilized. Both a conservative (e.g., Cl-) and reactive (e.g., Cs137) tracers with continuous step and rectangular pulse source functions are modeled. Sensitivity factors for skin thickness, fracture aperture, porosity, diffusion coefficient, and retardation coefficient are used to compare the effects of fracture skins on solute transport.

Analyses suggest that solute transport in the fracture can be either enhanced or retarded depending on the skin properties relative to the matrix. If fracture skin is less porous than the matrix, it generally behaves as a barrier to matrix diffusion and results in higher solute concentration in the fracture than expected without the skins. Because of sorption and decay, the skin effects on reactive solutes are not as great as on conservative solutes. In addition to diffusion, sorption, and decay, fracture length and aperture exert control over residence time and breakthrough concentrations of solutes. The longer the fracture, the longer is the residence time, and the smaller the aperture, the lower is the breakthrough concentrations.

The sensitivity analyses demonstrate that skin porosity and diffusivity have the greatest effects on solute concentration in the fracture followed by the impact of skin retardation for the reactive solutes and the influence of skin thickness and fracture aperture for the conservative solutes. Generally, solute concentration in the fracture increases with decreasing skin porosity, diffusivity, and retardation, especially when skins are thick. Back-diffusion is also shown to be an important process to control the solute concentrations in the fracture when the fracture is subject to pulses of solute. It is most pronounced when the concentration in the fracture becomes significantly lower than the concentrations in the skin and matrix to cause a shift in the direction of concentration gradient.


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CHARACTERIZATION, VARIATIONS, AND CONTROLS OF REEF-RIMMED CARBONATE FORESLOPES

Ted Eric Playton, Ph.D.

The University of Texas at Austin, 2008

Supervisor: Charles Kerans

283 pages, 85 references, 2 tables

Allochthonous, seaward-dipping deposits that flank reef-rimmed carbonate platforms (reef-rimmed carbonate foreslopes) display a spectrum of deposit types, seismic-scale stratal architecture, and bed-scale heterogeneity due to diverse sediment sources and resedimentation processes. This variability has resulted in a lack of consistent characterization approaches, and has made the development of predictive models that link carbonate foreslope deposit types to stratal architecture challenging. This study uses data from outcrops, including the Upper Devonian of the Canning Basin, Western Australia and the Upper Permian of the Delaware Basin, West Texas, and examples from literature to provide 1) an approach for characterizing reef-rimmed carbonate foreslopes in terms of deposit types and architecture, 2) conceptual models that outline the variations that exist, and 3) discussion of the intrinsic and extrinsic factors that control the observed variations.

The primary depositional elements that construct reef-rimmed carbonate foreslopes can be categorized as 1) debris elements (breccias and blocks) from brittle reef failure, 2) grain-dominated elements (grainstones and rudstones) from offbank transport of sand and gravel, and 3) mud-dominated elements (mud-dominated fabrics) that record relative foreslope quiescence and fine-grained periplatform shedding. The fundamental stratal geometries observed are 1) accretionary margins, characterized by margin-to-foreslope interfingering and clinoforms, and 2) escarpment margins, characterized by aggrading-retrograding margin architecture and foreslope onlap. The combinations of element proportions, element distribution, stratal geometry, bed- to bedset-scale architecture, and depositional profile scale that exist in carbonate foreslopes range widely, warranting multiple depositional models.

The deposit type and architectural variations observed in detail from Upper Devonian and Upper Permian outcrops of the Canning Basin, Western Australia, and the Delaware Basin, West Texas, respectively, are linked to differing scales of superimposed accommodation change and reef faunal assemblage. Observations from other outcrops and extensive literature review display further controlling factors that affect carbonate foreslope development, such as platform morphology, oceanographic conditions, slope height, tectonic setting, and siliciclastic input, suggesting a multi-variable interplay of controls. These controls dictate the productivity and resedimentation of the contributing sediment factories, and/or influence the development of the carbonate platform system as a whole. Knowledge and classification of carbonate foreslope deposit types, architecture, and controls not only improve understanding of these complex systems, but also allow for the development of predictive relationships for economic purposes.

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GROUNDWATER DECISION SUPPORT: AN INTEGRATED ASSESSMENT LINKING CAUSAL NARRATIVES, NUMERICAL MODELS, AND COMBINATORIAL SEARCH TECHNIQUES TO DETERMINE AVAILABLE YIELD FOR AN AQUIFER SYSTEM

Suzanne Alise Pierce, Ph.D.

The University of Texas at Austin , 2006

Co-Supervisors John M. Sharp, Jr. & David J. Eaton

Meeting future water demands requires sustainable management of aquifer resources. Over-abstraction of aquifer systems may occur if inequitable and inefficient methods, which do not consider science or people, are used to determine groundwater allocation and management strategies. The complexity of water resource issues is caused by the interconnectedness of hydrologic systems with other biophysical and social systems, such that competing requirements and non-linear behavior often overwhelm decision-makers and inhibit the creation of clear management strategies. A groundwater decision support system (GWDSS) is constructed to address the complexities associated with determining an acceptable groundwater allocation policy. Stakeholder concerns were gathered via elicitive interviews for inclusion in the GWDSS to link stakeholder input with a groundwater simulation-optimization model. GWDSS is a software tool that supports the implementation of a multi-disciplinary methodology consistent with the nature of water resource allocation problems for calculating the available yield of an aquifer

A loosely coupled simulation-optimization system, GWDSS is based on a pre-existing two-dimensional groundwater flow model for the Barton Springs segment of the Edwards aquifer. This test case is a karst aquifer undergoing rapid urbanization in central Texas . Active stakeholder groups in the region have vested interests in management strategies for the resource, and provided social inputs that serve as soft constraints for a tabu search optimization algorithm. Tabu is a meta-heuristic algorithm that uses query-based search techniques to gather knowledge about an objective and identify a list of deterministic solutions for consideration by a decision-maker. The tabu algorithm is applied to the transient version of the Barton Springs groundwater model to rank management scenarios ordinally. This method determines a set of feasible solutions, within the bounds of physical system behavior and community defined constraints, for extraction policies.

The GWDSS addresses the issue of aquifer sustainability by merging existing, spatially-variant, numerical groundwater models with stakeholder narratives into a relational database structure that is compatible with meta-heuristic optimization searches. This approach allows for more generalized management decisions to be mediated by a vetted scientific groundwater model and permits the determination of an available yield that incorporates both social considerations and aquifer performance in an integrated manner.


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FRACTURE PATTERN PREDICTION USING GEOMECHANICAL MODELS INCORPORATING DIAGENESIS, WITH COMPARISON TO OUTCROP DATA, CAMBRIAN ERIBOLL GROUP SANDSTONES, NORTHWESTERN SCOTLAND AND CORE OBSERVATIONS, TERTIARY MIRADOR FORMATION SANDSTONES, LLANOS FOOTHILLS COLOMBIA

Edgar A. Pinzon, M.S. Geo. Sci.

The University of Texas at Austin , 2007

 

Supervisor: Stephen E. Laubach

Effective and accurate characterization of fracture populations is a key for hydrocarbon reservoir assessments. The challenge is that fractures in the subsurface are exceedingly difficult to sample in meaningful ways. Outcrop studies have been an important source of information on fracture patterns providing better knowledge of the distribution, connectivity and geometry of fracture patterns. By establishing an analogy to outcrop observations, limited core data on can be used to better understand subsurface fracture patterns, leading to more accurate fracture permeability and flow pattern prediction. Using geomechanical models to simulate fracture pattern development is one way to systematically generalize the detailed observations of outcrop fractures in a specific locality to the general problem of prediction of fractures in the subsurface. Here, I use a combined methodology for fracture pattern description, which includes macro and micro scale observations of fractures and cements in Cambrian Eriboll Formation outcrops and Eocene Mirador Formation core. I use a geomechanical model that simulates fracture growth under the influence of concurrent diagenesis (cement precipitation). I focused on the attributes of fracture size (aperture and length).

The Eriboll Formation outcrops are unusually well-preserved examples of opening-mode fractures (veins and joints) with a great exposure of fracture size distributions. Using photographic and conventional mapping techniques, I generated fracture trace maps at the outcrop level at a scale of 1:10. Combining macro fracture observations with measurements along scanlines, petrography, fluid-inclusion analysis and high-resolution automated scanning electron microscopy (SEM), I found three preferred orientations for the fracture patterns at the outcrop: NS, NE and EW. From microstructural observations, I found that the current fracture pattern is the result of superimposed deformations that produced NS fractures of different ages that share a common strike but that differ in dip and in cross section show consistent crosscutting relations. Mirador sandstone cores have microfractures that exhibit size scaling that follows a power-law similar to those in the Eriboll. Mirador fracture openness predictions based on diagenesis resemble those found in the outcrop analog. Rock mechanical properties, subcritical crack index, diagenesis, mechanical layer thickness and strains measured from outcrop and subsurface rocks were used as an input for a geomechanical fracture pattern simulator (the geomechanical model Joints , Olson, 2007). I generated plots of fracture patterns that I compared to outcrop patterns. I used the same procedure to predict patterns for Mirador reservoir rocks.

My results show how geomechanical models that incorporate fracture and diagenesis can help make outcrop more germane to subsurface fracture prediction.

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NATURE AND SOURCE OF MINERALIZING FLUIDS AT THE PRESIDIO MINE, SHAFTER DISTRICT, PRESIDIO COUNTY, TEXAS

Fabienne Michèle Rambaud, M.S. Geo. Sci.

The University of Texas at Austin, 2005

Supervisor: J. Richard Kyle

The object of this research is to determine the nature and source of the mineralizing fluids that formed the Presidio Zn-Pb-Ag deposit, and to determine the relationship of the Presidio deposit to the rest of the Shafter district, including the Red Hills porphyry Cu-Mo deposit, exposed about 7 km to the west. The Presidio deposit is located in the Trans-Pecos mid-Tertiary volcanic field, near the Chinati Mountain caldera margin. Deformation of the Permian and Cretaceous strata has been attributed to the late Cretaceous to early Eocene Laramide Orogeny, with additional effects related to local caldera development. The ore-hosting Permian carbonates are highly fractured below the pre-Cretaceous unconformity, which allowed mineralizing fluids to form manto deposits. Recent studies have established that the Red Hills intrusion is of Laramide age (64 Ma). Thus, mineralization in the Shafter district is unlikely to be related to the 32 Ma Chinati Mountain caldera. A plutonic body extending from the Red Hills to the east could have been the source of mineralizing fluids that flowed eastward (and upward) creating a metal zonation from Cu-Mo to Zn-Pb-Ag. Extensive cores drilled between Shafter and Red Hills provide a valuable data base to attempt to link the two parts of the system.

A fluid inclusion study was performed on calcite and quartz samples collected in the Presidio mine and on calcite, quartz, and sphalerite collected from deep core intercepts west of the mine. Based on eutectic behavior of fluid inclusions two possible mineralizing fluids are suggested. H 2O-NaCl-KCl and H 2O-NaCl-CaCl 2. Both could represent a magmatic hydrothermal system.

Isotopic studies of calcite revealed that oxygen isotopes of formation waters are between 17 and 6‰ VSMOW. The spread of δ 18O values overall is interpreted to result from a mixing of high δ 18O values fluids, likely caused by high temperature exchange in the sedimentary rocks, with small amounts of meteoric water or other low δ 18O fluid.

Carbon isotope results suggest input of CO 2 and/or CH 4 likely from organic compounds in underlying sedimentary strata.

Sulfur isotope analyses show a narrow δ 34S range near 0 ‰ CDT and suggest a magmatic source for the sulfur involved in sulfide mineralization. Fractionation indicated by sulfide pairs suggests a mineralization temperature of 170° to 294° C.

The metal zonation, fluid inclusion, and stable isotope data suggest a magmatic source, probably from a largely buried Laramide-age magmatic system that produced a hydrothermal system that cooled laterally (Red Hills to Shafter), vertically, and over time, perhaps in response to fluid mixing.

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FACIES ANALYSIS OF THE PLIOCENE GROS MORNE FORMATION, SOUTHERN BASIN TRINIDAD

Meera Ramoutar, M.A.

The University of Texas at Austin, 2008

Supervisor: Ron Steel

The Gros Morne Formation was deposited in Trinidad's Southern Basin during a major Early Pliocene progradational phase of a northerly lobe complex of the paleo-Orinoco Delta. This study of the Gros Morne Formation provides details of the paleo-Orinoco shelf edge and upper slope, i.e., of the growth of the paleo-Orinoco shelf margin during a fourth-order progradational cycle.

Evaluation of the Gros Morne Formation at the Guayaguyare study location identified twelve lithofacies within the succession that developed as three environmental facies associations. These are the delta-front, outer-shelf/prodelta and upper-slope associations. The vertical juxtaposition of these strongly suggest that the Gros Morne is a regressive, upwards-shallowing deltaic succession that gradually built out across the shelf edge to supply the deepwater slope with turbidite sand lobes, mass transport complexes and slumped/collapsed sand units.

Within the depositional cycle of the Gros Morne observed in nearby well data individual, smaller-scale coarsening-upward packages can be clearly identified and can be tied into the measured outcrop profile. These higher frequency cycles, possibly fifth or even sixth-order cycles within the Gros Morne, represent shorter timescale autogenic lobe shifts, such as are seen on Modern and Holcene deltas.

Although the Gros Morne Formation displays similar characteristics to offshore reservoirs in the Columbus Basin, it lacks the vertical thickness that these reservoirs display due to a possible lack of growth faulting that greatly enhances the reservoir thicknesses and leads to economic reserves.

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FORECASTING U.S. CRUDE OIL PRICES FROM 1945 TO 1972

Terry L. Ramsey, Ph.D.

University of Texas at Austin, 2003

Supervisor: William Fisher

The most critical component of resource evaluation is the future price of the resource. This study takes the view that resource economics could do a better job of estimating resource prices by better representation of the resource "production functions" and how they relate to other economic activities.

A methodology has been developed for the pricing of resources that generalizes the concept of production function to a dynamic market where production functions become transactions. Transactions are not limited by the Cobb-Douglas production formulation. All transactions have the same fundamental structure which facilitates analyzing and interpreting data; provides a common tool for representing multiple transactions in complicated market processes for pricing products; simplifies the development of resource economic models; and, does it all in a dynamic environment. The methodology is illustrated by estimating US oil prices for the period 1945 - 1972 and by predicting market performance in two other models.

Interpretations of the empirical studies of Cobb-Douglas suggest the exact differential as the basis for how resources combine to form products which would generalize the concept of production functions. Empirical analysis encourages adoption of this viewpoint. By combining the exact differential with properties of a homogeneous system, the resulting model defines a new economic property the economic potential which relates the microscopic properties of economic activity to the performance of the total economy. The economic potential, μ, is a truncated exponential distribution that relates the price of a resource to the probability of that resource being purchased to form a product depending upon the minimum price, μο, and the mean return β. The probabilities of different conditions of price, cost, and average returns for any resource or product are given by Exp[ -((μ - μο)/β)] which is easy to remember and a rather beautiful proposition.

The economic potential is shown to be a driving force, moving the infinitely complex economy toward equilibrium which provides the means of relating different types of production functions and other economic activities. In so doing, the economic potential provides a powerful tool for correlation of a wide variety of pricing data. The diversity of applications and their duration suggests by induction that the exact differential, and the economic potential applies to all resources and products. The economic potential also relates widely different viewpoints of consumer choice including Daniel Kahneman's laboratory study of economic decision making, which earned him the 2002 Nobel Laureate in economics, and Daniel Bernouill's expected utility for maximization of wealth.

The exact differential and the economic potential generalize the concept of a production function to a time dependent process for combining resources to produce products that is designated as a transaction. Seven different types of transactions for resources are defined. Growth versus production is clarified, and transaction sets are used to represent complex real transactions.

The time dependent process of combining transactions can be defined in terms of transaction rates by calculus, but a component of the transaction rate, the contact rate, can only be determined empirically. The rate of transactions for four different industries and twelve different innovations are established empirically leading to an estimate of the contact rate given by 0.5*Exp[ -((μ - μο)/β)] . Transaction rates define differential equations for sets of transactions involving both multiple resources and products, and complex market pricing processes. The differential equation sets are solved numerically to make projections that are summarized numerically and graphically.

Simply defining the transactions is not enough. How the transactions are linked is important. Branch Point Analysis was developed for this purpose based upon the idea that although the market is constantly changing the relative rates of change in competing resources would be constant. Branch Point Analysis is illustrated for the energy market where the extent of competition of oil, gas, and coal is evaluated, as well as, the impact of government regulations.

Having laid out what constitutes a transaction and how to solve multiple transactions describing a process defining resources, an oil pricing model is constructed. Empirical analysis of the resources defines the transactions and transaction parameters. Branch Point Analysis relates how the transactions are linked. The empirical transaction analysis simplifies the problem of estimating the oil price by reducing it to two autocatalytic transactions coupled by their common dependence upon the target oil price set by State Regulatory bodies. Based upon the previous empirical analysis everything else can be safely neglected.

The computed real oil price model results are compared to actual real prices over the period 1945 to 1972. This period was selected because oil imports were negligibly small, in the sense that excess producing capacity in the U.S. set prices. Even with Federal and State governments policies influencing domestic oil prices, the subsequent oil pricing model is straight forward in development and solution. The oil pricing model results clearly forecast the shape of the price changes, but the curve is shifted in time by about five years or in real price by about $ 0.50. The methodology works in the sense of capturing pricing trends, but more work does need to be done to refine the estimates.

Two additional models were developed. The three example models show that incremental improvement in results were realized as more transactions were included. The technology demands a knowledge of the market: if you leave out important intermediate transactions you pay for it with reduced quality of results.

The objective of this dissertation was to contribute toward the development of a resource economic methodology that is general enough in form to be useful to industry professionals for estimating resource prices. This objective was realized by defining both the transactions and the transaction parameters which comprise the dynamic market processes governing resource prices.

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INFLUENCE OF RESERVOIR CHARACTER AND ARCHITECTURE ON HYDROCARBON DISTRIBUTION AND PRODUCTION IN THE MIOCENE OF STARFAK AND TIGER SHOAL FIELDS, OFFSHORE LOUISIANA

Claudia Rassi, Ph.D.

The University of Texas at Austin, 2002

Supervisor: William L. Fisher

Reservoir properties and production performance have been assumed to be controlled by their sequence stratigraphic position and the systems tract in which they are found. This hypothesis has been tested in a dataset from two mature gas fields, located ten miles offshore Louisiana. Available data included several decades of production history, various geophysical logs of 155 wells, sidewall core and special core analyses, which provide full information on hydrocarbon distribution and type, reservoir lithology, porosity, permeability, and production characteristics. The systems tracts of the Miocene study interval (60 fourth-order and 10 third-order sequences) were characterized with thickness and net sand maps, facies interpretation, and production evaluation. The three systems tracts of the fourth-order sequences (lowstand, transgressive, and highstand) show different trends in rock properties, such as porosity, permeability, or sand content. Each systems tract can be characterized with a typical range of values for its reservoir properties. These reservoir characteristics are clearly different for each of the three fourth-order systems tracts. In contrast, the data of the third-order sequences show high variability. The values of porosity of the three systems tracts do not differ significantly from each other and prediction is impossible with high confidence.

The sequence stratigraphic framework was linked to production information by (1) analyzing the average monthly production rate per perforated foot of fourth-order systems tracts and by (2) correlating to producing facies of each fourth-order systems tract. The strongest producers were found in facies of lowstand and highstand systems tracts and ranked highest. The incorporation of depositional facies interpretation into the fourth-order framework allows more detailed production estimation. Facies data also confirm the general picture of the systems tracts regarding rock properties, but they reveal differences among the facies types that could not be detected during the analysis of entire fourth-order systems tracts. One end product of this research is a database that stores all the information collected during the research, with customized search options that present a quick overview of systems tracts information. The application of this database is limited to stratigraphic units produced by similar depositional environments.

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SEDIMENTOLOGY AND DEPOSITIONAL HISTORY OF THE LATE CENOZOIC GILA GROUP IN THE CENTRAL DUNCAN BASIN, GREENLEE COUNTY, SOUTHEAST ARIZONA

Bradley Hamilton Reid, MSGeoSci

The University of Texas at Austin, 2002

Supervisor: Richard T. Buffler

This study documents the sedimentation and depositional history of the Upper Pliocene to Lower Pleistocene Upper Gila Group basin fill in the central Duncan basin, Greenlee County, southeast Arizona. The north-northwest trending intermontane Duncan basin is uniquely situated near the junction of the southern Basin and Range, Transition Zone, Colorado Plateau, and Rio Grande rift physiographic provinces, all of which had some influence on the structural evolution of the slightly asymmetric basin.

Forty-one stratigraphic sections, mostly the Upper Gila Group, located between the towns of Duncan and Three Way, Arizona, were measured and described to determine a facies classification of the basin fill deposits. Seven depositional facies were recognized. Their lateral and vertical distribution within measured sections and mapped areas were the basis for defining six significant depositional elements used to reconstruct the Plio-Pleistocene depositional history and paleogeography of the central Duncan basin. The six depositional elements include: streamflood-dominated alluvial fans, distal sheetflood alluvial fan, axial braided fluvial, floodbasin, lacustrine, and high basin stand deposits.

The streamflood-dominated alluvial fans are prominent along the southwest margin of the central Duncan basin, and are characterized by four distinct fan associations that were all locally sourced from the Peloncillo Mountains to the west. These fans generally prograded east and onlapped and interfingered with an areally extensive floodbasin that occupied much of the central Duncan basin. This floodbasin acted as a catchment area for the fine-grained sediments sourced from the alluvial fans systems along the basin margins. Parts of the floodbasin near Duncan were occupied intermittently by extensive freshwater lakes with benthic conditions that supported diatom growth. A prominent distal sheetflood alluvial fan occupied the northern part of the field area. It represents the distal portion of a prominent southeast prograding axial alluvial fan system sourced from the elevated Morenci block at the head of the basin. An axial braided fluvial system also was sourced from the Morenci block and flowed southeast along the southwest margin of the basin and dispersed into the floodbasin.

Deposition of the Gila Group basin fill terminated with the deposition of dominantly alluvial fan deposits locally sourced from the northeastern basin margin. These gravel deposits cap high mountain-front mesas in the Duncan basin and are similar to terminal basin fill deposits in other basins that are known regionally as the high basin stand (HBS). They were deposited just prior to and/or during entrenchment by the modern Gila River between 2.0 - 1.0 Ma, and are a coarse-grained response to a climatic and/or a tectonic shift during the latest Pliocene and early Pleistocene.

A Blancan-aged horse molar, Equus simplicidens, found in the Upper Gila Group, permits stratigraphic correlation to other nearby studies, and suggests that the Gila Group deposits in the central Duncan basin are primarily late Pliocene to early Pleistocene (3.7 - 1.0 Ma).


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PRELIMINARY CHARACTERIZATION OF THE VALLEY-FILL AQUIFER IN FORTYMILE WASH, SOUTHWESTERN NEVADA

Theodore Roosevelt Ressler, MSGeoSci

The University of Texas at Austin, 2001



Data on the stratigraphy, sedimentary characteristics, and hydraulic properties of the alluvium to the east and southeast of Yucca Mountain are limited. Such limitations regarding the alluvium present uncertainties in current groundwater models used in performance assessments of the proposed nuclear waste repository at Yucca Mountain.

The modern entrenched channel of Fortymile Wash, a large desert wash located east-southeast of Yucca Mountain in southwestern Nevada, provides several laterally continuous, well-exposed outcrops of the alluvium. The features observed in the nearsurface alluvium are presently the best available analogs of the alluvium in the saturated zone. Eight diagnostic sedimentary facies were identified based on grain size, sedimentary features, and geometry. The alluvium of Fortymile Wash consists of predominantly conglomerate and sandstone interpreted as braided stream deposits. The majority of the alluvium is clast-supported, well organized, and contains relatively small amounts of matrix fill. Only minor deposits of sediment gravity flows were observed in the alluvium of Fortymile Wash, but such deposits are more abundant on the transverse fans rimming Fortymile Wash.

Gamma ray and density measurements were collected from outcrop to develop simulated wireline logs for future comparison of the nearsurface observations to the subsurface alluvium. Outcrop density profiles were found to be a function of the clast content of the valley-fill. The density profiles clearly identify the cobble and boulder layers within the alluvium. Outcrop gamma profiles were dominantly influenced by the feldspar contained in the volcanic clasts of the alluvium. Most of the facies did not have a characteristic gamma ray response. In one exposure, a paleosol horizon had a notable gamma ray low that was attributed to the low clast and clay contents of the paleosol.

Hydraulic estimates for the different facies were developed from laboratory permeameter tests completed on samples of the alluvium, and from empirical relations based on the results of grain size analyses completed on samples of the alluvium. Porosity estimates ranged from 0.21 to 0.42, with the coarser grained samples having lower porosities than the finer grained samples. Permeability within the valley-fill varies over at least three orders of magnitude. The least permeable facies are the paleosol horizons, which are commonly laterally extensive for hundreds of meters. The low permeability and lateral continuity of the paleosol horizons suggest these facies may impart a strong stratification that could have implications for vertical and horizontal groundwater movement. The most permeable facies is horizontally stratified gravel and sand, which is also the volumetrically dominant facies observed in outcrop.

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LARAMIDE EXHUMATION AND HEATING IN SOUTHEASTERN ARIZONA: LOW-TEMPERATURE THERMAL HISTORY AND IMPLICATIONS FOR ZIRCON FISSION-TRACK SYSTEMATICS

Brook Colleen Daun Riley, Ph.D.

The University of Texas at Austin, 2004

Supervisor: Mark Cloos

222 pages, 113 references

Fission-track (FT) ages of zircon from Mesozoic sandstones were analyzed to address provenance and post-depositional thermal history of Laramide synorogenic strata. Upper Cretaceous samples show a complex provenance, with significant recycling from underlying rocks. FT peak ages from 14 Jura-Cretaceous sandstones include populations of 570-165, 140-82, and 68-42 Ma. Older single-grain ages (1000-600 Ma) indicate long-term sub-annealing temperatures (<180°C, up to 260°C, depending on single-grain response to heating) for portions of the source area. Older FT ages present in all sampled units indicate little burial of the Jura-Cretaceous rocks prior to recycling into the Upper Cretaceous; record little variation in the thermal signature of recycled crustal detritus; and show that the older Jurassic and Cretaceous rocks likely provided an important source for the Fort Crittenden Formation. The uniformity of FT ages necessitates that source rocks all record essentially the same thermal signatures. Accordingly, the relative abundance of rock units in the source terrane was rather uniform, and there was no preferential exhumation of one source area over another.

Some zircons show evidence for significant post-depositional thermal annealing; these strata reached temperatures sufficient to anneal fission tracks in some grains (c. 180°C-260°C). Thicknesses of overlying units was likely less than 2 km; as such, the FT age structure is not purely the result of burial. Regionally, samples with Paleocene-Eocene reset peak ages coincide with proximity to magmatic bodies (75-40 Ma). Besides conductive heating, a hydrothermal system may have locally modified these rocks, causing preferential resetting of certain zircons. This setting provides an opportunity to investigate controls on single-grain thermal response. Geochemical and crystallinity data indicate a correlation between old crystallization ages, high U+Th concentrations, elevated alpha-damage, and young reset FT ages. Resetting occurred in grains with higher radiation damage, and less damaged grains have a higher temperature of track retention and therefore retain a primary detrital signature. Zircon color is related in part to increasing radiation damage, and can be used for identifying different thermal events in both the pre- and post-depositional history of individual zircons. In this study, honey and colorless grains essentially behave as one population in all data sets. Based on these data, this study establishes criteria for identifying reset grains in detrital populations, and suggests revisions in the current methodology.


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JURASSIC-RECENT TECTONIC AND STRATIGRAPHIC HISTORY OF THE CHORTIS BLOCK
OF HONDURAS AND NICARAGUA (NORTHERN CENTRAL AMERICA)

Robert Douglas Rogers, Ph.D.

The University of Texas at Austin, 2003

Supervisor: Paul Mann
264 pages, 214 references, 35 plates

I document four post-Jurassic tectonic events recorded in the geology of the Chortis block of northern Central America within the context of the regional evolution of the Caribbean plate and the southernmost North American Cordillera. The earliest event is Aptian-early Cenomanian, intra-arc rifting followed by late Cretaceous inversion of the rift basin in the Frey Pedro range of east-central Honduras. A 3.5-km-thick stratigraphic section of clastic, carbonate, volcaniclastic and volcanic rocks were deposited in the intra-arc rift and on its rift shoulders. The geochemistry of rift-related volcanic rocks shows magmatic arc affinity.
The northwest-directed Colon fold-thrust belt of eastern Honduras and the Nicaragua Rise and adjacent island arc Siuna belt of northern Nicaragua, record the late Cretaceous collision between the south-facing margin of the Chortis block and the northeastward-moving Caribbean arc system. This previously unrecognized arc-continent collision can be traced for a distance of 350 km across Honduras and the Nicaragua Rise. North trending rifting of the western Chortis block and NNW-SSE transtensional extension of northern Honduras and the offshore Honduran borderlands reveal Miocene to Recent divergence between the Caribbean and North America plates. Observed boundary-normal extension occurs where the angle between the plate boundary fault and the Caribbean motion vector is greater than 10 and boundary-parallel transtension where the angle is between 5 and 10.

P-wave tomographic images of the mantle beneath northern Central America reveal a detached slab of the subducted Cocos plate. Landscape features of the region above the detached slab are consistent with epeirogenic uplift produced by mantle upwelling following slab breakoff between 10 and 4 Ma.
Correlation of regional aeromagnetic data with outcrop exposures allows subdivision of the Chortis block into five terranes: 1) Central Chortis with continental Paleozoic basement; 2) Eastern Chortis with Jurassic metasedimentary basement; 3) Southern Chortis of low magnetic intensity and covered by Miocene volcanic strata; 4) Siuna with oceanic island arc basement; and 5) Northern Chortis where early Tertiary magmatism overprints the Central and Eastern Chortis terranes. Common geologic and geophysical characteristics of the Chortis terranes and Mexico terranes allow improved reconstructions of the region prior to its Tertiary fragmentation.

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PETROGENESIS OF THE LLANO GRANITES, CENTRAL TEXAS: FORMATION MECHANISMS AND TECTONIC IMPLICATIONS OF RADIOGENIC ISOTOPES

Elizabeth Ann Roller, M.S. Geo. Sci.

The University of Texas at Austin, 2004

Supervisor: James N. Connelly

116 pages, 130 references

The production of granitic magmas subsequent to deformation and metamorphism is a common feature of many orogens. Many models attempt to explain this magmatism with respect to orogenic processes, whereas others have viewed this magmatism as purely anorogenic, unrelated to any prior tectonic events. Late- to post-tectonic granites of the Llano uplift (at the present crustal level) offer an ideal suite of rocks, in a well-constrained tectonic setting, to contribute to this ongoing debate.

The Llano uplift of central Texas contains 1.12-1.07 Ga granites that intruded soon after 1.15-1.12 Ga Grenvillian metamorphism and deformation. Existing geochemical data from these granites indicate that they are A-type, but do not constrain a formation mechanism or source for these magmas. Radiogenic isotopic compositions of the granites were analyzed to further constrain the petrogenetic model for their formation. Sm/Nd data indicate that these granites contain a ca. 1.5-1.2 Ga crustal component, similar in age to the pre-existing Llano crust. Pb isotopic data indicate that they had a common source whose Pb isotopic composition matches that of the pre-existing Llano crust at ca. 1.1 Ga. Evidence for incorporation of a Llano crustal component supports a model for magma generation in the Llano region in which delamination of the lithosphere, associated with detachment of the subducted slab, causes melting of an already depleted lower crust. Thus, these Llano granites appear to be related to Grenville orogenesis.

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EFFECTS OF CLIMATE CHANGE ON MAMMALIAN FAUNA COMPOSITION AND STRUCTURE DURING THE ADVENT OF NORTH AMERICAN CONTINENTAL GLACIATION IN THE PLIOCENE

Dennis Russell Ruez, Jr., Ph.D.

The University of Texas at Austin, 2007

Supervisor: Christopher J. Bell

857 pages, 832 references, 11 tables, 2 volumes

The cooling preceding the beginning of North American continental glaciation is beautifully represented by the thick fluvial and lacustrine sequences of the Pliocene Glenns Ferry Formation at the Hagerman Fossil Beds National Monument (HAFO), Idaho. This time interval is commonly studied because it contains the elevated global temperatures predicted to result from continued anthropogenic warming. The fossil mammals at HAFO were examined to see the effects of climate change on past mammalian assemblages.

The nature of the fossiliferous localities at HAFO was documented to establish which localities could be considered in situ. Additionally, the structural architecture of the beds was mapped to establish an idealized stratigraphic datum to which localities were tied. This facilitated temporal comparison of the widespread localities at HAFO. Second, a high-resolution record of climate change was created using global climate models to predict which oceanic areas varied in temperature in concert with HAFO during the middle Pliocene. Data from deep-sea cores from those oceanic areas were combined to create a proxy temperature pattern; such a detailed record from terrestrial data in the Glenns Ferry Formation is not currently possible.

Selected mammalian groups, carnivorans, insectivorans, and leporids, were examined in light of the established climatic patterns. The cooling through the lower portion of the Glenns Ferry Formation corresponds to variation in the morphology of individual species, the relative abundance of species, and the species-level diversity of mammalian groups. There is a return to warm temperatures near the top of the section at HAFO, and the mammals returned to the conditions exhibited before the cool-temperature extreme. This faunal resilience, however, occurred over hundreds of thousands of years.

The final paleoecologic approach established correlations between the species diversity of groups of modern mammals and modern climatic values. Many modern groups were found to be highly-significantly correlated to climate, but when the established predictive equations were applied to HAFO, the results were variable. Estimates of annual precipitation varied widely, depending on the taxonomic group, and also deviated from precipitation estimates from sedimentology. Temperature patterns were more consistent with each other and with the pattern of the deep-sea core proxy.

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SEQUENCE ARCHITECTURE OF A LATE GUADALUPIAN CARBONATE RIMMED SHELF, WALNUT CANYON, NEW MEXICO

Jason Windrow Rush, M.S.

The University of Texas at Austin, 2001

Co-Supervisors: William Fisher, Charles Kerans

The Tansill Formation (uppermost Guadalupian), as exposed along canyons in Carlsbad Caverns National Park, provides a unique opportunity to document a near-complete platform-to-basin transition of a carbonate rimmed shelf system. More than 1000-m of measured section and extensive bed tracing using photomosaics enabled construction of a detailed sequence-stratigraphic framework for the 1.2-km, depositionally dip-oriented, exposures along lower Walnut Canyon. Comparatively rapid evolution in Late Permian fusulinacean faunas aided in further refinement and provides independent verification of the hierarchy of stratigraphic cyclicity. This integrated, biostratigraphically constrained, high-resolution stratigraphic framework consists of one composite sequences (CS) (long term), four high-frequency sequences (HFS) (intermediate term), and at least forty high-frequency cycle sets (short term).

Evolutionary stages of the Tansill system began with marine transgression over the karst-modified Hairpin dolomite (Guadalupian-25 HFS). Maximum accommodation was reached during the Guadaluplan-26 HFS as shelf crest grainstones aggraded constructing 25-m of relief. The Guadaluplan-27 BFS was dominated by lowstand sedimentation as indicated by platform karstification, margin failure, basinward thickening of the Reichelina lamarensis zone, and a downward shift of coastal onlap. The base of the Wuchiapingian-1 HFS is marked by an obvious facies tract offset, similar lowstand sedimentation characterized by large clastic-filled fractures lacking marine cements, and a four-fold basinward expansion of the Paraboultonia zone within 0.1-km.

This newly proposed high-resolution sequence framework provides a more-dynamic and inclusive depositional model by incorporating observations at various scales. During lowstand, brittle failure of the platform margin generates subaerially-exposed fracture systems and increases accommodation. Across the shelf, subtle topography develops as differential compaction occurs across near vertical, en echelon, penecontemporaneous faults and joints. Rapid basinward thickening of fusulinacean zones, absence of mud-dominated rock fabrics, lowstand-induced margin failure, karstification, and sequence architecture provides: (1) evidence of significant sea level fall (>60-m) during Tansill time, and (2) supports Dunham's marginal mound interpretation.


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SEISMIC AND STRATIGRAPHIC INTERPRETATION OF THE MORICHITO SUBBASIN, EASTERN VENEZUELAN BASIN

Migdalys Beatriz Salazar, MSGeoSci

The University of Texas at Austin , 2008

Supervisors: William Fisher and Lorena Moscardelli

150 pages, 71 references, 4 tables

The Morichito Subbasin is a southwest-northeast oriented depocenter that is located in the Eastern Venezuelan Foreland Basin (EVFB). The Morichito Subbasin covers an approximate area of 1,000 km2 between the Serranía del Interior fold and thrust belt and the Pirital High. This basin was formed during the Neogene as the result of complex transpressional interactions between the Caribbean and South-American plates. Previous studies have tried to address the tectonostratigraphic significance of the Morichito Subbasin but about 1,800 km2 recently acquired 3D seismic volumes allowed us to expand our understanding of this subbasin. The relevance of the Morichito Subbasin lies in the fact that it provides a valuable stratigraphic record that can be used to unveil the timing of the main deformational events that took place in this portion of the EVFB.

This work presents the tectonostratigraphic evolution of the Morichito Subbasin by defining four sequences (Units I to IV). These units were defined based on the integration of well logs and biostratigraphic information with geomorphological interpretations that were performed using 3D seismic data. Unit I (E. Miocene to M. Miocene) was deposited in shallow marine environments (the Carapita Formation) and its areal coverage extends to the south, beyond the boundaries of the Morichito Subbasin suggesting that Unit I pre-dates the formation of the Pirital High. Unit II (M. Miocene) is composed of alluvial fan deposits (the Morichito Formation) that were derived from the Serranía del Interior fold and thrust belt; pinch-out relationships against the Pirital High indicates that Unit II was contemporaneous with the Pirital thrusting event. Units III (L. Miocene to E. Pliocene) and IV (E. Pliocene to Recent) are composed of shallow marine and fluvial deposits (Las Piedras and Mesa Formations). These two units represent the final phases of basin infilling when tectonic activity and subsidence were at lower rates.

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QUANTITATIVE SEISMIC GEOMORPHOLOGY OF PLIOCENE AND MIOCENE-AGE FLUVIODELTAIC RESERVOIRS IN THE NORTHERN GULF OF MEXICO SHELF PROVINCE

Carla Maria Sanchez, M.S. GeoSci

The University of Texas at Austin , 2006

Supervisor: Lesli J. Wood

Fluvio-deltaic reservoirs contain at least 600 billion BOE worldwide. However, these reservoir types are notorious for low percentage of mobile oil recovery due to their complex architecture. Predictive relationships relating reservoir quality to its depositional system morphology offer the opportunity to reduce uncertainty in reservoir characterization and field development for these complex systems. The study area encompasses 900 sq km of 3D seismic and over 170 well log suites from several producing hydrocarbon fields in the Northern Gulf of Mexico Shelf Province . Fluvio-deltaic reservoirs of Miocene and Pliocene-age, which have been studied before in a sequence stratigraphic context, are the focus of this study.

Results suggest, for both ages of systems, trends indicating an increase in width:depth ratios as sinuosity decreases. Miocene data show width:depth ratios decreasing as Vsh increases, whereas Pliocene data show a similar trend but with significant scattering.

Pliocene-age channel widths range from 80 to 140 meters. On the other hand, Miocene-age channel widths lay between 700 and 1,000 meters. Width:depth ratios for Pliocene and Miocene-age channels are very different. These data show Miocene-age channels to be much wider than their younger Pliocene counterparts. A cyclic pattern of low and high W:D can be recognized in this parameter variability through the Pliocene. Such cyclicity may be due to a variety of influences including base-level changes at the shoreline, or climatic changes in the drainage basin.

Data from oxygen isotope studies suggest that eustatic sea level changes were of higher magnitude and frequency during the Pliocene than during the Miocene. Likewise, climate is believed to have experienced similar large magnitude and higher frequency changes during the Pliocene. Such dramatic changes in base level and climate would have affected the ability of fluvial and deltaic systems to become stable. These high frequency and large magnitude changes could have hampered the ability of Pliocene-age channels to adjust their shape and pattern to the type of sediment load, resulting in a lack of relationships between channel sediment load type, sinuosity, and width to depth ratios.

The Atchafalaya seems to represent a better analog system to Miocene-age channels based on the width, depth and W:D ranges of these modern rivers. Based strictly on the morphometrics of the channels, the Trinity River seems to qualify as the most appropriate modern analog for the Pliocene-age channels in the study area.

It has been suggested that during Miocene times the U.S. Gulf Coast region climate was warm and humid. Assuming these climatic conditions, for Miocene-age fluvial systems in the northern Gulf of Mexico, equations developed for rivers located in sub-humid settings have the strongest application to understanding Miocene discharge in the northern Gulf of Mexico . Paleodischarge estimates in the order of 10 5 cubic meters per second have been obtained for Miocene-age fluvio-deltaic systems in the study area using an empirical relationship for tropical and sub-humid climate.

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SEQUENCE STRATIGRAPHY AND STRUCTURAL FRAMEWORK OF SOUTHEAST CARIBBEAN MARGIN: OFFSHORE ORINOCO DELTA, VENEZUELA

Marel Alexandra Sanchez, M.S.Geo.Sci.

The University of Texas at Austin, 2001

Supervisor: William L. Fisher
Co-Supervisor: Lesli J. Wood

The Orinoco Delta offshore is an exploration frontier along the northeast margin of the South American continent. The area is limited to the north by the transpressional southeast-Caribbean margin and to the south by the South American continent. Hydrocarbon production in this region has been ongoing for over half century, however, most of the studies in the more eastward deep-water areas have been unpublished due to the active exploration. New regional 2D seismic data, collected in 600-km-long sections out to the eastern limit of the southeastern Caribbean margin, reveal the region's major Mesozoic to Recent tectono-stratigraphic features. A chronostratigraphic framework for the Orinoco Delta offshore was defined by interpreting the deep seismic lines with sparse well and seismic information located in the continental margin. This study integrated valuable information in the deep water section with these results from: 1) Deep Sea Drilling Program (DSDP) sites 143-144 (Demerara Plateau-offshore Suriname), 2) Deep Sea Drilling Program (DSDP) Leg 77 (southeast Gulf of Mexico), 3) Ocean Drilling Program (ODP) Legs 156 and 171A (north of the Barbados Accretionary Complex), and 4) Ocean Drilling Program (ODP) Leg 159 (Côte d'Ivoire-Ghana, West Africa). These chronostratigraphic data assisted in establishing the tectonic and depositional history of the basin fill.

Five regional sequences bounded by major unconformities define the margin's tectono-stratigraphic framework. These sequences are as follows: 1) megasequence 1: Late Jurassic syn-rift and post rift sequence associated with the Tethys Ocean opening, 2) megasequence 2: Early Cretaceous sequence related to the South Atlantic Ocean opening, 3) megasequence 3: Late Cretaceous-Paleocene passive margin sequence, 4) megasequence 4: Early Tertiary passive margin sequence, and 5) megasequence 5: foredeep sequence related to the Late Tertiary Caribbean compressional tectonics. The latest sequence represents a 3-5 km-thick Oligocene-to-Recent sediment column, whose architecture is influenced by local and regional tectonics, high rates of sediment supply from the Orinoco River drainage system, and major changes in sea level.
The Orinoco Delta offshore area's tectono-sequence development reflects the region's transition from rift, to passive, to compressional margin history. The Tethys Ocean opening during the Late Jurassic resulted in non-marine to marine carbonate sedimentation in graben and half-graben structures over an extending continental to transitional crust. During the Early Cretaceous there are evidence of a transform margin in the northern Demerara Plateau, and creation of the pull-part basin in the deep Guyana Basin area, related to the South Atlantic Ocean opening. The drift phase of the newly formed Atlantic Ocean during the Late Cretaceous to the Lower Tertiary was controlled by changes in sea level. During the Neogene to Recent, structural deformation associated with of the transpressional Caribbean margin working in concert with the Orinoco Delta to dominate the basin architecture.

The proto-Orinoco and Orinoco drainage systems have been the major sediment sources since the Middle Miocene. Late Miocene-to-Pleistocene-age growth faulting and shale mobilization dominate the recent and present-day basin fill. Marine currents and the area's active tectonics contributed to the complex sediment dispersion and deposition of the Quaternary Orinoco fan.

Tectonics along the Caribbean margin results in two primary types of deformation activities. These activities are: 1) Minor reactivation of basement faults that influence the nature of the Neogene shelf edge architecture, and may even result in activation of deep mobile substrates (salt?) and 2) extensional and compressional deformation of the Neogene section above a common detachment surface, resulting in the development of growth faults, shale mobilization and diapirism, and even seafloor argilokinetic volcanism (observed in the eastern Trinidad and the Barbados Accretionary Prism).

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FORWARD SEISMIC MODELING OF A TIDAL BAR-INCISED VALLEY COMPLEX TO DELINEATE RESERVOIR ARCHITECTURE: SEGO SANDSTONE OUTCROPS OF EASTERN UTAH

Hasan Sarikaya, MSGeoSci

The University of Texas at Austin, 2002

Co-Supervisors: William L. Fisher and Lesli J. Wood

The worldwide importance of resources in fluvial-deltaic (clastic) reservoirs dictate that improved techniques should be developed to quantify and delineate their architecture. Although outcrop analogues provide a significant body of knowledge and data on interwell-scale facies architecture, sand-body geometry, and on the character and continuity of bounding surfaces, they are commonly measured at a scale that is below resolution of conventional exploration seismic data. Forward seismic modeling (FSM) of outcrop and subsurface sections provide a bridge for this resolution gap.

FSM was applied to the outcrops of Sego Sandstone Member (Campanian) of the Mancos Shale, which is comprised of four, fourth-order tidal shelf delta and shoreline successions cut by lowstand distributary channels and incised valleys cropping out extensively in the Book Cliffs of eastern Utah. Information from outcrop, including a detailed stratigraphic framework, rock velocity, facies, sedimentology and petrography, were combined with adjacent subsurface sonic and density logs immediately behind the outcrop to create a series of seismic models. These models provide information on how the stratal relationships and architecture of tidal-bar complexes, channels and valleys are represented in seismic data.

The digital images of outcrop belts form a gridded template for modeling using a vertical incidence technique. Cross-section grids were populated with the density and velocity values measured from the outcrop and subsurface facies. Scripts written in MatLab were run to compute seismic responses, and 1D and 2D seismic models with various frequencies (30, 60, 100 Hz) of Ricker wavelet, trace spacing (10, 25 m) and thicknesses (1X, 3X, 5X) were constructed.

Results show that reflections are formed as a consequence of impedance distribution; and delineation of the architectural elements depends upon element dimensions (width, thickness and length), seismic frequency and trace spacing. Thinning of architectural elements often removed them from the resolution window and caused a simulation of erosion or lapout on the seismic section. Although the seismic response across key bounding surfaces (lowstand unconformities, flooding surfaces, regressive surfaces of marine erosion), varied depending on the cross-surface facies associations the regional extent of this intermittent response formed a continuity of seismic response enabling long distance correlation. Within tidal bar complexes, the relationship between tidal-bar sands and overlying highly, bioturbated bar tops is imaged in seismic and can easily be mistaken for an unconformity.


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REGIONAL GEOCHEMICAL STUDY OF THE WESTERN INTERIOR PLAINS AQUIFER SYSTEM AND THE GREAT PLAINS AQUIFER SYSTEM IN THE MID-CONTINENT, UNITED STATES

Rosario Vasquez Scheerhorn, Ph. D

The University of Texas at Austin , 2005

Supervisor: Jay L. Banner

A wide range of chemical and isotopic variability characterizes the Great Plains Aquifer System (GP) and the Western Interior Plains Aquifer System (WIP), reflecting a range of fluid mixing processes and water:rock interaction. The study area extends 1200 km from eastern Colorado to central Missouri and from Nebraska to the Oklahoma panhandle. The GP comprises Cretaceous sandstones that are both overlain and underlain by shales. The WIP comprises carbonates and sandstones of Cambrian through Mississippian age. This aquifer system underlies Pennsylvanian through Jurassic shales and overlies the Precambrian basement.

The WIP groundwater has been classified into three distinct groups; Group 1 is a fresh water originating in the Ozark Plateau, Group 2 is a saline groundwater possibly originating in the Colorado Front Range, and Group 3, originating in the Anadarko Basin , is the most saline groundwater of the three. Results from fluid mixing models suggest that the groundwater in the WIP can be explained by the mixing between these three groundwater groups. The salinity of the WIP could be the result of two different mechanisms, halite dissolution and evaporation of seawater.

The GP groundwater can be divided into two groups; GP1 is a fresh groundwater present in the unconfined portion of the aquifer while GP2 is a saline groundwater present in the confined portion of the aquifer. GP2 groundwater acquired its salinity from interaction with groundwaters upwelling from the Permian shales and evaporites. The strontium isotopic composition of GP2 also implies that these groundwaters have mixed with groundwater migrating upwards from the Pennsylvanian shales. The light isotopic signature of both GP1 and GP2 suggests that this groundwater recharged at higher elevations and colder climatic conditions in the Colorado Front Range. Fluid-mixing modeling results between the two groundwater types suggest that the groundwater from the confined system and the groundwater from the unconfined system are not mixing.

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PRECISION GEOLOGICAL MAPPING WITH A TABLET PC

Dominique K. Schmid, B.S.

The University of Texas at Austin , May 2005

Supervisor: Mark Helper

44 pages, 10 references, 1 plate

This study explores the possibilities of a tablet PC for geologic mapping, particularly focusing on accuracy of the equipment and ease with which a person can become proficient in a short period of time. Experiments were performed with a tablet PC and a hand-held mapping-grade GPS receiver (Trimble GeoXT) to compare accuracy and efficiency. Geologic contacts were walked in an area of meter-scale folds and digitized into mapping software to produce a detailed (1:3000) map. Digitized lines were constructed by creating "polylines" from vertices captured with a GPS receiver and by manually drawing lines in GIS software; point data (sample and photo location, strike and dip locations, etc.) were also collected. This study demonstrates: 1) a tablet PC can be successfully used for field mapping; 2) the accuracy of tablet internal DGPS receivers is comparable to the accuracy of more expensive, mapping-grade GPS receivers; and 3) scaled-down GIS software can be learned quickly by novices. The tablet PC holds promise as an excellent mapping tool but the technology is still too new and problems make tablet use an inefficient alternative to traditional approaches to field work, or to data collection with a mapping-grade GPS receiver. Multiple hardware and software problems plague tablets, reducing their efficiency and reliability in the field. Becoming proficient with a tablet PC requires more time than is available during normal field work, making it necessary to learn tablet programs and tools before going into the field. When a tablet PC runs smoothly, however, it is a tremendously useful tool in the field and improvements in hardware and software could make the tablet a reliable tool for field mapping.

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COMMUNITY PALEOECOLOGY OF THE PENNSYLVANIAN WINCHELL FORMATION, NORTH-CENTRAL TEXAS

Christie Lynn Schneider, Ph.D.

The University of Texas at Austin, 2003

Supervisor: James Sprinkle

306 pages, 192 references

Many previous fossil community studies have focussed on biodiversity issues without examining community structure and dynamics. The research herein investigates how much community information beyond biodiversity can be recovered.

An echinoid Lagerstätten in the Lake Brownwood Spillway locality of the Pennsylvanian (Missourian) Winchell Formation contains four new species of echinoids. Archaeocidarids also host Crurithyris and bryozoan epibionts on their spines. The relationship between the echinoids and epibionts was commensal, benefitting the epibionts. Epibionts received associational defense, transport, water currents, settlement sites, and decreased competition.

Four recurring community types occurred in Winchell outcrops from the Lake Brownwood Spillway, Perrin, and RP1, and in Kansas outcrops from the Kansas City, Lansing, and Shawnee Groups. Large productids, Neospirifer, echinoids, and Aviculopinna are characteristic fauna of communities in argillaceous limestones. In shales, highly abundant bryozoans, small attaching brachiopods, and crinoids characterize one community type, whereas small attaching brachiopods and tubuliporate bryozoans plus Neospirifer, productids, and Myalina typify a different community type. In fine grain limestones, abundant Composita and echinoids, along with Antiquatonia and bryozoans characterize another community type. Other distinct, non-recurring communities included those containing abundant echinoids in the Brownwood black shale Lagerstätte; Composita and Acanthopecten in packstone layers in the Brownwood black shale, and diverse bivalves plus Parajuresania and Minilya in concretions at Brownwood.

Insights into community structure, not just changes in community diversity through time, are possible with detailed sampling and analysis. Ordination analyses revealed limestone/shale patterns in scatterplots and a ternary gradient arrangement of unbaffled, fenestellid-baffled, and phylloid algae-baffled communities. Competition is inferred to occur between large productid brachiopods. Spatial competition is directly seen in fenestellid-baffled shale communities as interspecific overgrowths and non-interference by conspecifics. Epibiosis is very common in all shale communities and provides evidence for unpreserved substrates, but the biotic or abiotic nature of these host surfaces is unknown.

Cluster analyses were performed on Brownwood samples using Bambach's (1983) guild classification, guilds based on the potential for strong competitive interactions, and individual taxa. Guild and taxon analyses agree on large-scale community types, but differ in sample arrangement within units and lithologies. Researcher bias in sampling appears to be minimal.

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APPLICATION OF GROUND-BASED LIDAR TO CONSTRAIN TOPOGRAPHIC STRIKE-VARIABILITY AND FACIES PROPORTIONS OF PROGRADATIONAL SAN ANDRES FORMATION CLINOFORMS, LAST CHANCE CANYON, NM

Samuel Zephyr Scott, M.S. Geo. Sci.

The University of Texas at Austin, 2003

Supervisor: Charles Kerans

110 pages, 97 references, 1 table

Progradational mixed-carbonate/siliciclastic San Andres Formation clinoforms at Last Chance Canyon, New Mexico were quantitatively mapped and modeled using techniques developed for use with LIDAR (Light Dectection and Ranging). Fundamental questions addressed by this thesis are: (1) What is the nature of topographic strike-variability within a progradational mixed-siliciclastic setting, (2) How is topgraphic strike variability related to a sequence stratigraphic framework?, and (3) Can construction of a LIDAR-based digital outcrop model provide insight into the three dimensional relationship between clinoform morphology and resultant clinothem facies distributions within high-frequency cycles (HFCs)?

Chapter one relates facies distributions within HFCs to depositional processes predominantly utilizing measured section and mapping data. Results indicate highstand Guadalupian 9 (G9) high-frequency sequence (HFS) clinoforms built basinward as a sinuous front composed of promontories and reentrants. Low relief lenticular bioherms composed of sub-wave base open-marine fauna colonized upper-slope settings in response to reduced sediment supply subsequent to HFC maximum flood. Resumed production of the carbonate factory near the previous slope break filled topographic lows between intervening autochthonous open marine bioherms during progradation of regressive hemicycles. Differential along-strike topography on the upper-slope was largely filled at HFC termini during the early highstand of the G9 HFS, while during the late-highstand strike exposures exhibit nested topographic depressions that persist through multiple HFCs. It is suggested that persistent topographic lows were generated and accentuated by siliciclastic bypass of the slope in response to increasing slope declivity, and a narrowing of the area of the carbonate factory. Focus of bypassing siliciclastic sands through persistent topographic lows reduced siliciclastic influx on adjacent topographic highs and provided a stable substrate for nucleation of a late highstand build-up.

Chapter 2 documents construction of a LIDAR based Digital Outcrop Model (DOM), and demonstrates topographic strike-variability existed throughout the G9 HFS. Quantitative mapping of clinoform surfaces demonstrates the nature of siliciclastic bypass is sensitive to an equilibrium threshold in slope angle of approximately 15 degrees. When clinoform declivity exceeds this threshold, the slope is entrenched through bypass of shelf-derived siliciclastics. A reduction in HFC boundary slope angle below 15 degrees in youngest clinoforms is suggested to reflect a period of forced regression. Finally results of facies modeling for HFC 2 developed using experimental variograms derived from catergorical facies values along measured sections and a deterministic indicator kriging algorithm are presented. Results honor measured section date and further indicate clinoforms during the G9 highstand prograded as a sinuous clinoform margin characterized by promontories and reentrants.

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MODELING AND IMAGING OF GROUND PENETRATING RADAR DATA

Armando Ruggiero Sena D’Anna, Ph.D.

The University of Texas at Austin, 2004

Supervisors: Paul L. Stoffa and Mrinal K. Sen

Ground Penetrating Radar (GPR) is an active and non-invasive exploration technique based on the propagation of electromagnetic waves in the subsurface. Modeling of GPR data is important because it helps us with data interpretation and forms the basis (solution to the forward problem) for most iterative inversion techniques. Conversely, migration (or imaging) is a type of inversion technique (backward propagation) that creates an image related to the subsurface reflectivity and can be used to estimate the model parameters of the media that affect the propagation of the waves. However, for practical applications, modeling and migration techniques must be fast, accurate and efficient.

I have developed a fast, efficient and accurate GPR modeling technique for stratified media (isotropic and laterally homogeneous layers) based on the invariant imbedding or reflectivity technique. To test the results obtained with this technique, and have a general tool for modeling of GPR data in heterogeneous, dispersive and isotropic media, I have implemented a 3D explicit Finite Difference Time Domain (FDTD) technique. The FDTD formalism is presented in conjunction with a discussion of the electromagnetic dispersion mechanisms that affect the GPR signal in most geologic media. I show that the results obtained with the reflectivity and FDTD techniques are nearly identical for laterally homogeneous media. Real GPR data is used to study the capabilities and practical aspects that affect the accuracy of the reflectivity technique.

I have developed a new technique for migration of GPR data in heterogeneous and lossy media. I have implemented the technique in 2D media and presented the formalism for its extension to 3D media. The new technique, based on the Split Step Fourier migration technique, allows us to efficiently include the dispersion and attenuation effects in the media. An approximation of homogeneous plane waves, which do not add new restrictions to the Split Step Fourier technique, gives greater stability to the imaging technique allowing us to migrate the data through thicknesses up to three times the characteristic skin depths of the media computed at the dominant frequency of the GPR signal.


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HYDROLOGICAL APPLICATIONS OF GRAVITY RECOVERY AND CLIMATE EXPERIMENT (GRACE)

Ki-Weon Seo, Ph.D.

The University of Texas at Austin, 2005

Supervisor: Clark R. Wilson

131 pages, 32 references, 5 tables

The Gravity Recovery and Climate Experiment (GRACE) satellite mis­sion jointly supported by the National Aeronautics and Space Administration (NASA) and Deutsche Forschungsanstalt fur Luft und Raumfart (DLR) was launched March, 2002. GRACE provides monthly Stokes coefficients of spheri­cal harmonics (SH) representing the global gravity field and changes over time with unprecedented accuracy. Gravity changes estimated from GRACE in­clude effects from planets, tides, solid Earth deformation, and motion within the fluid envelopes of the atmosphere and hydrosphere. After corrections for known or predictable effects, it is possible to isolate changes due to redistribu­tion of water mass, especially related to storage changes in river basins. This study addresses four issues related to hydrological applications of GRACE: The first is to examine optimum filter designs to obtain the maximum spatial resolution of water mass load changes from GRACE Stokes coefficients. The second is to understand and estimate GRACE aliasing errors related to the space-time sampling of the satellite ground track. The third is to recover water storage changes and associated errors over large river basins, and the fourth is to examine the feasibility of sampling of the gravity potential anomalies along the ground track for dealiasing.

The optimum filter for recovering average storage in a river basin should minimize the influence of GRACE errors and maximize the signal to noise ra­tio. One strategy is to adjust the filter on a monthly basis according to signal changes. To define water mass signal changes in this filter design strategy, nu­merical predictions from the Global Land Data Assimilation Scheme (GLDAS) and Estimating the Circulation and Climate of Ocean (ECCO) ocean model are used. A time variable filter can perform better than a fixed coefficient filter if good model predictions are available.

ECCO, GLDAS, and atmospheric model mass fields can also be used to study the nature and causes of aliasing. Simulated GRACE Stokes coefficients are obtained from gravity potential differences along the GRACE ground track during a month. The difference between the estimated Stokes coefficients from the ground-track sampling and true average Stokes coefficients computed from the global fields is aliasing error. Aliasing errors from land and oceans sharply increase up to SH degree 15 and slowly increase thereafter. Atmospheric alias­ing error is significant below SH degree 15. Single SH mass load with single frequency sinusoidal temporal variations have aliasing errors approximately predicted by Kaula's resonance formula. Aliasing errors from isolated Gaus-sian mass loads are dependent on the latitude of the load since GRACE spatial sampling is denser at high latitudes than at low latitudes.

Global water mass loads are recovered from GRACE using various schemes, including the time-variable optimum filter. Degree amplitude spectra of GRACE Stokes coefficients show peaks at SH degree 15, 30, 45 and so on, in agreement with the aliasing study with synthetic data. The largest water mass load changes are observed in low latitude basins such as the Amazon, Congo and Ganges, and show clear seasonal signals. GRACE signals are comparable to GLDAS prediction, providing some validation GRACE result.

Gravity potential difference along GRACE ground track are computed from climate model fields, and 2-day gridded maps are estimated. Using the different time scales between changes in terrestrial water storage and atmo­spheric surface pressure, high frequency atmospheric surface pressure fields can be removed. This suggests the possibility of improved dealiasing, using preprocessing of the ground track samples prior to estimation of SH fields.


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INTEGRATION OF GEOLOGICAL AND PETROPHYSICAL DATA IN RESERVOIR CHARACTERIZATION OF PENNSYLVANIAN UPPER MORROW “C-SAND” IN WILBURTON FIELD, MORTON COUNTY, KANSAS

Martha Patricia Serrano Perez, M. S. Geo. Sci.

The University of Texas at Austin, 2005

 

Supervisor: William Fisher

The Morrow C-sand reservoir at Wilburton Field is an incised-valley-fill fluvial sandstone of Pennsylvanian age. It is compartmentalized into five flow units, each of which possesses particular geological and petrophysical characteristics. Understanding the scale, geometry, and internal complexity of this depositional system is important because these sandstones represent the main hydrocarbon reservoirs in Wilburton Field. Described core, wire-line logs, petrophysical measurements and production data were integrated for Morrow C-sand depositional model and reservoir characterization.

Morrow C-sand valley was incised into the underlying marine section during a relative drop in sea level. As relative sea level rose in a series of pulses, the valley was filled with fluvial sediments consisting of thick channel sandstone facies that comprise the Wilburton Field reservoir and floodplain facies. The vertical succession is composed of coarse-grained sandstones which represent amalgamated stacked channels, and point bar sediments separated by thin overbank deposits. Following fluvial sediment deposition, a marine transgression commenced during which some of the channel sands were reworked by marine processes. The relative sea level continued to rise and an overlying section of black marine shales was deposited sealing the Morrow C-sand valley.

Five flow units were defined within the Morrow C-sand reservoir based on stratigraphy and petrophysical characteristics. These flow units are genetically related to the original stratigraphy of the valley-fill. Reservoir quality is controlled by the internal heterogeneities of the depositional facies.

The performance of wells in the field is determined by the number and quality of the flow units from which they produce. The presence of non-reservoir rocks within the valley-fill, such as floodplain deposits, provides permeability barriers and obstacle to fluid flow.


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CHARACTERIZING HETEROGENEITY IN LOW-PERMEABILITY STRATA AND ITS CONTROL ON FLUID FLOW AND SOLUTE TRANSPORT BY THERMALHALINE FREE CONVECTION

Mingjuan Shi, Ph.D.

The University of Texas at Austin, 2005

Supervisor: John M. Sharp, Jr.

Studies of salinity-driven free convection across low-permeability strata indicate that permeability heterogeneity is an important factor in controlling solute transport in the system.Heterogeneity exists at different scales in natural geological materials and presents a significant challenge to many aspects of geological science and petroleum studies. The traditional Rayleigh number criterion is overly conservative in predicting thermohaline convection in a heterogeneous system. Heterogeneity effects are investigated with numerical models to study salinity-driven groundwater flow and solute transport through heterogeneous low-permeability units. Monte Carlo stochastic simulations of the permeability fields are applied to model saturated variable-density flow and to examine how the internal structure of the permeability field controls fluid flow and contaminant transport in low-permeability strata. Simulations show that dense plumes take preferential pathways to sink through low-permeability strata; patch analysis using percolation theory shows the threshold permeability for the onset of free convection can be as low as 10 -16 m 2 when the mean permeability of the distribution is 10 -18 m 2. The threshold permeability for a percolation cluster decreases with increasing concentration gradient, vertical correlation length, mean permeability, and standard deviation. The connectedness of the relative high permeability zones is important in initiating and controlling plume fingers of free convection. Numerical modeling results also show that free convection occurs more easily and often when there is a sand or sandstone layer on top of the low-permeability shale layer or below with different boundary conditions.

For a fractured low-permeability shale layer, free convection can easily occur along the fracture plane which suggests the inadequacy of two-dimensional fracture model for simulating free convection in parallel-plate discrete fractures. Free convection through hydraulically active tiny fractures can be an important mechanism for flow and solute transport even though these tiny fractures in the shale unit can not be detected by vertical boreholes and flow in most part of the unit is diffusion-dominated.


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MANTLE HETEROGENEITY AND FLOW FROM SEISMIC AND GEODYNAMIC CONSTRAINTS

Nathan Alan Simmons, Ph.D.

The University of Texas at Austin , 2007

Supervisor: Stephen Grand

255 pages, 108 references, 7 tables

I have developed 3-D models of mantle heterogeneity that satisfy seismic and geodynamic observations. The seismic constraints include body wave travel times of multi-bounce mantle and core shear waves. The geodynamic constraints include the Earth's gravity field, dynamic surface topography, tectonic plate motions and the excess ellipticity of the core-mantle boundary. These geodynamic observations are directly dependent upon density perturbations in the mantle which are the driving force of mantle flow. Furthermore, the effect of density anomalies on these geodynamic observables is dependent upon the viscosity of the mantle and whether or not there are boundaries to vertical flow within the mantle. Assuming a linear relation between seismic velocity and density, I tested several hypotheses for how the mantle convects by jointly inverting the seismic and geodynamic data. The data were best fit by a model assuming whole mantle convection with no internal layers that strongly inhibit vertical flow.

The simultaneous inversion of seismic and geodynamic observations requires knowledge of the link between seismic velocity and density perturbations in the mantle. Therefore, I have tested several radially-symmetric profiles of density-velocity scaling from mineral physics studies which assume that all lateral heterogeneity is generated by lateral temperature variations. Integration of the optimum density-velocity conversion profile into the joint modeling framework has yielded mantle-scale models of seismic velocity and thermally-induced density perturbations. These models satisfy the combined dataset to a reasonably high degree implying that variations of temperature are the primary cause of mantle seismic heterogeneity outside of the roots of continental cratons. Using inversion techniques, I have also found a 3D density-velocity relationship in the mantle thereby revealing density perturbations associated with compositional variability. Compositional buoyancy of the cratons is clearly detected and i ntrinsically-dense material is found within the mid-mantle extension of the rising African superplume structure. This high-density component within the superplume hinders the buoyancy of the structure and possibly redirects the flow within. Collectively, these models yield a better understanding of the dynamics of the mantle.

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TOMOGRAPHIC INVESTIGATION OF THE UPPER MANTLE VELOCITY STRUCTURE BENEATH THE TRANSITION FROM THE WESTERN COLORADO PLATEAU TO THE GREAT BASIN

Christopher Robert Sine, B.S.

The University of Texas at Austin , 2007

Supervisor: Stephen Grand

112 pages, 52 references, 5 tables

The La RISTRA 1.5 project consisted of 18 broadband seismic stations deployed along a northwest trending line extending from the center of the Col¬orado Plateau into the Great Basin. Seismic P-wave and S-wave traveltime data from this project are inverted to determine mantle velocity perturba¬tions relative to the IASPE91 velocity model of Kennett and Engdahl (1991). The resulting two-dimensional tomographic image beneath this line extends the work of Gao et al. (2004), who, using the La RISTRA 1 dataset, inves¬tigated mantle structure from the Great Plains of west Texas, across the Rio Grande Rift, and into the center of the Colorado Plateau along a seismic line of the same orientation as La RISTRA 1.5. Combining the data from the two experiments we present continuous high resolution P-wave and S-wave veloc¬ity models from the Great Plains, across the Rio Grande Rift and the entire Colorado Plateau, and into the Basin and Range (Great Basin).

P-wave and S-wave inversions show a sharp contrast in mantle velocity beneath the transition zone from the Plateau to the highly extended Great Basin. The magnitude of this velocity anomaly appears to be too great to be due to temperature alone. Hydration and partial melting of the shallow mantle beneath the Great Basin is consistent with the hypothesis of hydration and subsequent heat input due to Cenozoic to Tertiary ?at-slab subduction and foundering of the Farallon plate beneath this area. The presence of partial melt or increased hydrogen in mantle olivine can account for large perturbations in seismic velocities. However, this does not explain the sharpness of the velocity gradient (12% S-wave velocity change over 100 km) beneath the Great Basin-Colorado Plateau transition. The sharpness of this transition may correspond to a boundary separating mantle lithospheres with ages di?ering by up to one Ga. A sharp contrast in the a?nity for melting, related to lithospheric age, from the mantle lithosphere of the Great Basin to that of the Colorado Plateau would control lithospheric alterations resulting from Farallon plate subduction and foundering. We believe that an age dependent contrast in melting a?nity across a mantle lithospheric boundary separating Great Basin and Colorado Plateau mantle lithosphere has resulted in the large and sharp velocity contrast observed in the tomographic models.

A seismically fast anomaly is imaged from depths of 300 to 600 km be¬neath the eastern Great Basin and western Colorado Plateau. The position of this anomaly corresponds roughly with the inferred location of foundering of the Farallon plate. We believe this anomaly represents a remnant of the Farallon plate or delaminated continental lithosphere present beneath southwestern North America. The volume of the anomaly is too large to represent a simple downgoing slab. Thus, this anomaly may represent a locus of downwelling Farallon plate or continental lithosphere.

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MARINE OIL POLLUTION: THE COST OF OIL SPILLS

Assel Ibragimovna Smagulova, M.A.

The University of Texas at Austin, 2002

Supervisor: Willem C.J. van Rensburg

In order to satisfy the growing demand, the petroleum industry produces and supplies the world with billions of tons of oil every year. As a vast amount of oil is moved around the world, this inevitably involves the risk of oil spillage into the marine environment.

The occurrence of major oil spill incidents has attracted the attention of the public and the media; this in turn has resulted in an escalated global awareness of the risk of oil spills and the damage they do to the environment.

Protecting the marine environment, while producing and transporting the oil, is a challenge that the petroleum industry meets every day. Despite the industry's best efforts to prevent oil spills, they do occur. In the event of an oil spill incident, the oil companies and shipowners face the great array of costs associated with the oil spills. The ultimate cost of oil spill is extremely complex, consisting of many other costs categories. Even a small oil spill can lead to extremely high costs.

This thesis is based on the statistical data obtained from statistical databases, relevant researches and studies, consent decrees, settlements, and oil spill histories.

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REGULARIZATION AND REDATUMING USING LEAST SQUARES AND CONJUGATE GRADIENTS

Daniel Ryan Smith, M.S.Geo.Sci.

The University of Texas at Austin, 2008

Supervisor: Mrinal K. Sen

86 pages, 55 references, 1 table

Irregularity in source and receiver spacing along with dead traces and noise can result in incomplete data causing spatial aliasing problems. In addition, phase distortions from sampling near-surface velocity variations can cause lateral reflector discontinuity which statics cannot handle. A method is developed to handle both these problems together as an inversion problem. Weighted, damped least squares are used to downward continue data by estimating the new wavefield at depth by minimizing the residual between the estimated wavefield and the observed wavefield and conjugate gradients are employed for optimization. The extrapolation operators are spatially varying phase-shifts applied within a Fourier integral operator. The Hessian in the least squares inversion is costly to compute, so conjugate gradients are employed to avoid computation of the Hessian as a matrix-matrix multiplication and instead reduce it to two matrix-vector multiplications. This reduces the total number of multiplication operations from Оn3 for the direct solution to Оn2 for the conjugate gradient method, where n is the number of trace locations.

I use a synthetic example as well as a real data example to demonstrate the method's effectiveness. The synthetic data are from an exploding reflector model where the traces have been generated by finite differences. It is designed to simulate an irregular, horizontal recording array above a horizontal line source with five point sources and a laterally variable background velocity. The resulting data are a sub-horizontal discontinuous reflector above steeply dipping diffractions. The method successfully removes the effects of the lateral velocity variations flattening the events and reconstructing the missing traces.

The real data comes from the Alberta Foothills of the Canadian Rocky Mountains acquired by Husky Oil Ltd. where the shot spacing is very irregular and therefore common receiver gathers are quite irregular. Moreover, the near-surface is highly heterogeneous due to varying topography and laterally varying velocity so the data suffers from lateral reflector incoherency. The method successfully reconstructs the data, still with some artifacts due to actual spatial aliasing, and improves lateral continuity of the reflectors also while suppressing ground roll.

Overall, the computational efficiency of the method is improved by an order of magnitude when compared to the direct inversion methods.

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MULTITAPER SPECTRAL ANALYSIS OF WIDE-ANGLE REFRACTION DATA FROM COSTA RICA FOR T* ESTIMATION

Sanjay Sood, M.S. Geo. Sci.

The University of Texas at Austin , 2007

Supervisor: Mrinal K. Sen & Harm Van Avendonk

The inputs and outputs of the Central American subduction zone have received attention from geoscientists of many disciplines in recent years. In order to have full understanding of subduction, it is important to have constraints on the nature of deep-seated magmatic processes and the composition of newly formed crust. In January to March and July 2005, I was associated with a group of scientists from the United States and Costa Rica that acquired two long seismic refraction lines parallel to and across the arc in Costa Rica to image the physical properties of the entire crust. Line1 runs almost SW-NE, across the arc in central Costa Rica from Pacific coast in the west to Atlantic coast in the east. We deployed 742 seismometers at nominal spacing of 200 m. Reftek “Texans” data loggers were used to record the data with a sampling interval of 4 msec. Twenty explosive shots ranging in size from 200 kg to 1025 kg were used. These sources were detonated at ~ 7.5 km interval along the profile to acquire seismic refraction data on this cross-section of the arc. The ultimate goal of the project is to infer subsurface temperature distribution that can be related to magmatic processes.

One approach to estimating temperature distribution is to map seismic attenuation distribution. Towards this goal, I have used the data from this line to map the variation of t* (path integrated attenuation) values across the volcanic arc using a method based on spectral ratios. I have compared several spectrum estimating techniques and demonstrated that a multitaper method is able to obtain robust estimates of spectra. I estimated the source by summing the spectra from near offset stations, a weighted running average of spectra with one km radius was taken to enhance the signal to noise ratio and a Random sampling was used to obtain more realistic estimates of the errors in the spectra. Finally I used a Spectral Ratio's method to calculate the slopes. Different frequency windows were used to calculate the least squares linear fit. My results show a large variation in the t* values. These fluctuations in the t* values are attributed to the large variations in the near site effects and scattering attenuation associated with them along the profile. Some anomalous t* values may be a result of focusing of seismic energy due to underlying velocity structure. The background noise plays an important role in the t* values as well. At larger source-receiver offsets the signal/noise ratio is lower. Consequently, we overestimate the amplitude of the higher frequency at large offsets. Contrary to the assumption of Spectral Ratio's method, attenuation seems to be frequency dependent for this data set.

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STRUCTURAL AND BASINAL ARCHITECTURE AND ACTIVE STRIKE-SLIP FAULTING OF THE EASTERN OFFSHORE AREA OF TRINIDAD

Manuel David Soto, M.S. Geo. Sci.

The University of Texas at Austin, 2007

Co-Supervisors: Paul Mann and William Fisher

Previous GPS-based geodetic studies and fault trenching in Trinidad have shown that the 50-km-long, linear, onland segment of the Central Range fault zone (CRFZ) accommodates at least 60% of the total rate of right-lateral displacement (~20 mm/yr) between the Caribbean and South American plates. 2D and 3D seismic reflection data from a 60-km-long and 30-km-wide swath of the eastern shelf of Trinidad (block 2AB) were used to map the eastern offshore extension of this potentially seismogenic and hazardous fault system and to document its deformation and control on Middle Miocene and younger clastic stratigraphy. Two unconformity surfaces and seafloor were mapped using the seismic data to generate isochron maps and to illustrate the close control of the CRFZ and associated secondary faults on small, clastic basins formed within and adjacent to anastomosing strands of the CRFZ right-lateral shear zone. The mapped surfaces include: 1) the middle Miocene angular unconformity, a prominent surface separating underlying thrust-deformed rocks from a much less deformed overlying section; 2) a Late Neogene angular unconformity that is developed locally within block 2AB; and 3) the seafloor of the eastern Trinidad shelf. Clastic sedimentary fill patterns identified on this isochron maps indicate a combined effect of strike-slip and reverse faulting (i.e., tectonic transpression) on the structure of the CRFZ, which is highly oblique to the interplate slip vector known from GPS studies. A family of east-west-striking faults with normal and possibly transtensional motions appears to have contributed to the creation of accommodation space within localized clastic depocenters south of the CRFZ.

3D seismic data reveals that the 60 km-long, offshore continuation of the CRFZ forms a prominent seafloor lineament and dextrally offsets a shallowly buried (83 m below sea level), late Quaternary fluvial channel by 322-506 m. Based on eustatic sea-level curve, I infer that the channel began to be incised at the beginning of the Last Glacial Maximum (LGM) ~30 ka and was subsequently offset in a right-lateral sense by the CRFZ. Using the offset amounts and our inferred age for the filled channel, I estimate a long-term slip along the fault of 17-19 mm/yr for the CRFZ. Because no documented earthquake has occurred on the Central Range since 1800, as much as 3.7 m of elastic strain may have accumulated on the CRFZ that could be released by a future magnitude >M7.5 earthquake.

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MICROBIAL INFLUENCE ON THE KINETICS OF KARSTIFICATION

Elspeth Susan Steinhauer, MSGeoSci

The University of Texas at Austin, 200

Supervisor: Philip Bennett

The traditional model of karst and cave formation is that of carbonic acid limestone dissolution, where biologically-produced CO2 in meteoric water reacts with and dissolves limestone. However, an alternative model has been proposed for several karst sysems where sulfide is abundant, known as sulfuric acid speleogenesis (SAS). Here, acid produced by chemoautotrophic sulfur-oxidizing bacteria (SOB) corrodes limestone while producing dissolved calcium and sulfate. Little is known about the rate of limestone dissolution due to SOB activity, or the nature of the microbe-limestone attachment and interaction.

The field site for this study is Lower Kane Cave, WY, an active SAS-formed cave where rapid steam H2S oxidation is associated with sulfur-oxidizing microbial mats. In this study, the rate of limestone dissolution due to microbial oxidation of reduced sulfur compounds was investigated using laboratory and field microcosms. Laboratory chemostat chamber experiments were designed to mimic the cave environment with and without SOB (native Kane Cave bacteria and Paracoccus versutus), and using different energy sources (thiosulfate, sulfide, and elemental sulfur stored in bacterial filaments).

Limestone dissolution rates of abiotic chemostat experiments from this study are comparable to those in previous literature. However, dissolution rates from the experiments with bacteria are 3-4 times faster than the abiotic control rates, a result which is consistent across duplicate experiments and between experiments using different types of SOB. This rate increase represents a complex chemical system influenced by the bacteria on the mineral surface. SEM images confirm that the limestone chips both in the cave and in the biotic chemostat chambers are uniformly covered in biofilm, and that the mineral surface beneath the biofilm is much more etched and corroded than the surface of limestone chips dissolving without bacteria. The results from the lab experiments and the cave microcosms suggest that a biofilm on limestone chips will physically and chemically separate the mineral surface from the bulk solution. Because the bacteria are generating acid directly on the mineral surface, a microenvironment develops beneath the biofilm with low-pH and low saturation state with respect to calcite. The neutrophilic sulfur oxidizing bacteria found in the cave and used in the experiments benefit from attachment to limestone (high buffering capacity), and create a microenvironment that triggers limestone corrosion at a rate several times faster than the abiotic rate.

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VARIABLE-DENSITY GROUNDWATER FLOW BENEATH THE WIND-TIDAL FLATS OF PADRE ISLAND

Joel Daniel Stevens, M.S.GeoSci

The University of Texas at Austin, 2007

Supervisor: John M. Sharp, Jr.

Field evidence for density-driven free convection, a potentially important groundwater transport process, has been examined at Padre Island National Seashore to determine if this phenomenon can develop under natural environmental conditions. Hitherto, this process had not been conclusively detected or measured in field scale hydrogeology. Field methods, including nested monitoring wells and time-lapse 3-D resistivity surveys, reveal evidence of variable-density groundwater flow in the wind-tidal flats. Evaporative concentration of groundwater near the water table resulted in unstable inverted density gradients, reduced groundwater levels, and reduced hydraulic gradients. These factors allowed plumes of dense fluid to migrate downward into less dense fluid which were observed in monitoring wells and 3-D resistivity surveys. This shows that the development and flow of variable-density fluids in groundwater can be detected and monitored through field techniques. It demonstrates that the development of density inversions may overcome the dissipating forces of dispersion and diffusion to create a sufficiently large unstable gradient to induce free convection.

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SENSITIVITY OF AVO REFLECTIVITY TO FLUID PROPERTIES IN POROUS MEDIA

Jason Andrew Stine, M.S. Geo. Sci.

The University of Texas at Austin, 2004

Supervisor: Robert Tatham

177 pages, 32 references

The Zoeppritz equations used in a typical reflection amplitude versus source-receiver offset (AVO) study to calculate the reflection and transmission coefficients do not directly consider the fluids filling the pore space in a porous solid medium. Although they account for the effects on the density and P-wave and S-wave velocities in porous solids, these equations neglect the movements of fluids with respect to the porous framework. In doing so, the effects of the permeability and viscosity of the fluids during flow are ignored. These properties may affect the energy reflected and transmitted at a boundary; therefore, they must be accounted for to give an accurate wave propagation model.

Biot theory considers the propagation of elastic waves in a porous elastic solid saturated by a viscous fluid. This theory accounts for the motion of fluids in the interconnected voids of a porous solid, assuming Darcian fluid flow. Biot theory accounts for the propagation of three waves, one rotational (shear) wave and two dilational waves (P-wave and slow wave). Reflection and transmission coefficients are calculated including Biot theory, showing potentially observable differences from the coefficients calculated using the Zoeppritz equations, for different physical situations.

The sensitivity of the reflection coefficients to different physical parameters is examined. The goal is to evaluate how the reflection coefficients change as individual parameters, such as viscosity or permeability, are varied, and which parameters affect the reflection coefficients the most. If the reflection coefficient does not change as a parameter is varied, there is no sensitivity to that parameter and information about that parameter cannot be extracted from the data. The sensitivity analysis is complimented by calculating partial derivatives of the expressions for the reflection coefficients with respect to individual parameters, particularly fluid parameters. With this approach, large values of the partial derivative imply large changes in reflection coefficients with respect to a physical parameter indicate the most sensitivity to that parameter in the reflection coefficient.

In Biot theory, the solid properties dominate over those of the fluids alone. The fluid properties only impact the reflection coefficients in a significant manner when there is a small contrast in the solid properties across a boundary. If the contrast in solid properties is too large, any effects caused by the fluid properties are insignificant compared to the solid effects. The three shale over sandstone models have too large of a contrast in solid properties to see fluid effects. Conversely, the six models of fluid boundaries within a reservoir sand all have little to no contrast in solid properties, so the fluid effects are evident. For gas-water interfaces, the observable changes in the P-P reflectivity are estimated to be as large as 5% for a 1% change in permeability and 15% for a 1% change in viscosity.

When the above criteria for observing the fluid effects are met, the P-wave has sensitivity to viscosity, sensitivity, and porosity, with the reflection coefficients giving the most sensitivity to changes in the fluid viscosity. The apparent sensitivity to porosity is mostly a response to the density change caused by the change in porosity, rather than direct effects of the porosity.

Theoretical AVO reflection coefficient curves based on Biot theory are inverted using two and three term AVO inversions based on approximations of Zoeppritz reflectivity. There is significant error in the parameters extracted by the inversion for both the two- and three-term AVO inversions. The three-term Aki and Richards (2002) inversion produces inaccurate values of the physical parameters across the boundary. Standard AVO inversion algorithms based on Zoeppritz reflectivity have problems accurately calculating parameters for a porous medium where fluids can move. An intercept and gradient interpretation algorithm based on Biot theory is desirable to accurately extract physical properties in porous media.

A second formulation for reflectivity in a porous elastic solid is examined. In this study the theory developed by de la Cruz and Spanos (1985) is modified from their high viscosity limits, to fit more common lighter-oil viscosity regimes. The equations of motion and boundary conditions developed as part of the Spanos theory are adapted for this application. The reflectivity problem is simplified to an eigenvalue problem, based on a number of assumptions. De la Cruz, Hube, and Spanos (1992) published their computed values of reflection coefficients for high viscosity fluids. However, the complexity of this theory makes it impractical, in this study, to follow through to calculation of reflection coefficients in a porous elastic solid.

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GEOCHEMISTRY, SEDIMENTOLOGY, AND MORPHOLOGY OF MUD VOLCANOES, EASTERN OFFSHORE TRINIDAD

Sean Michael Sullivan, M.S. Geo. Sci.

The University of Texas at Austin, 2005

Supervisor: Lesli J. Wood

The seafloor expulsion of hydrocarbon-rich fluids and fine-grained sediments originating from the deep subsurface influences the deep-marine topography, sediment pathways, and biota distribution in eastern offshore Trinidad. This study uses approximately 8,000 km 2 of 3D seismic data (imaging the subsurface in water depths of 100 to 1450 m) and both sedimentologic and geochemical data from 203 dropcores to understand: 1) the controls on the distribution and morphology of mud volcanoes, 2) how hydrocarbon seepage/mud volcanism impacts deep-marine life and sedimentation, and 3) the origin of hydrocarbon gases emitted from mud volcanoes.

Based on structural and bathymetric criteria using 3D seismic data, the mud volcanoes in the study area can be grouped into provinces: I) a mud ridge province, 2) a basin-fill province or 3) a fault-focused province. Methane-rich fluids seeping out of mud volcanoes provide a favorable environment for chemosynthetic life in the deep sea and cores taken near mud volcanoes contain bivalve, gastropod, and tubeworm fossils typical of hydrocarbon seep communities. Authigenic carbonates (formed from the oxidation of methane), pure white gas hydrate, and lithic clasts are other sedimentologic features present in the dropcores. Interstitial gas analysis of hydrocarbons (C i-C5 alkanes and alkenes ) and carbon isotope geochemistry of methane ( δ 13 C CH 4 = -119 to -58‰) confirms that the majority of gases at or near mud volcanoes are bacterial in origin with a few exceptions taken at mud volcano peaks (characterized by δ 13 C CH 4 values of -58 to -66 ‰ and low methane:ethane ratios), which result from a mixing between bacterial and thermogenic gases.

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STRUCTURAL EVOLUTION OF THE EAST CENTRAL BIG MARIA MOUNTAINS, MARIA FOLD AND THRUST BELT, SOUTHEASTERN CALIFORNIA

Vanessa Svihla, MS GeoSci

The University of Texas at Austin, 2003

Supervisor: Sharon Mosher

134 pages, 94 referemces, 5 color plates

The Maria Fold and Thrust Belt in southeastern California and western Arizona provides an excellent location to study Mesozoic contractional deformation in an intracratonal setting. Previous mapping and research have added greatly to our understanding, yet many questions about the tectonic evolution of this area remain. The influence of fluids, structural depth, plutonism, and other factors controlling the style and kinematics of Mesozoic deformation are not well constrained, yet these may be the keys to understanding differences between ranges and the processes resulting from intracratonal shortening. One of the largest ranges within this belt, the Big Maria Mountains of southeastern California, has fold vergence which is apparently anomalous, though this may be a result of poorly understood polyphase deformation and lack of geochronological control.

In this study, I investigated Mesozoic deformation in a portion of the overturned limb of a regional-scale recumbent syncline that is in contact with a Jurassic pluton. I have distinguished distinct phases of folding based on relative timing: F2a isoclinal folds, F2b sheath folds, F3 tight folds that have axial planes oblique to previous axial surfaces and foliation, and F4 open folds, which have fold axes that are close to horizontal. The most abundant (thousands) folds are F2a and F3 folds, although F2b folds are common (hundreds observed). F2a, F2b, and F3 folds occur at scales from mm to hundreds of meters F4 folds are less common (tens observed) on the outcrop (meters) scale but the entire area is affected by F4 folding on the thousands of meters scale. Based on style and orientation, F2a and F2b formed during one progressive noncoaxial deformation as a result of localized and distributed shear. F3 folds, which verge both to the north and the south, may be part of this progressive deformation but represent a transition to coaxial deformation. F4 folds and associated top-to-the-north thrusts formed later, most likely as a result of Late Cretaceous to early Tertiary Laramide deformation. The F2 deformation is associated with upper greenschist- to lower amphibolite-facies metamorphism.

I have refined previous models for the Big Maria Mountains by discovering that refolding is present and that the orientation of the contact between the pluton and the country rocks requires that the country rocks were intruded by the pluton prior to deformation. The kinematics of shearing that formed the F2 folds appear to be top-to-the-northeast, which is opposite of most folds in the Maria Fold and Thrust Belt. The Plomosa Mountains have similar vergence, as do late ductile structures in other ranges, so the fold kinematics within the Big Maria Mountains is not completely anomalous.


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RESPONSE OF THE BRAZOS RIVER DISPERSAL SYSTEM TO LATEST PLEISTOCENE CLIMATIC VARIATION AND EUSTATIC CHANGE

Dennis Ashton Sylvia, PhD

The University of Texas at Austin, 2002

Supervisor: William E. Galloway

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INVESTIGATION OF SURFACE ROUGHNESS OF NATURAL ROCK FRACTURES USING HIGH-RESOLUTION X-RAY COMPUTED TOMOGRAPHY AND LABORATORY FLOW TEST MEASUREMENTS

Clark Thompson, M.S. Geo. Sci.

The University of Texas at Austin, 2005

Supervisor: John M. Sharp, Jr.

Fluid flow through natural rock fractures is an important – and often dominant – factor in many aquifer and reservoir systems. Rock fractures are rough-walled, and this surface roughness introduces complexities. The analytically-derivable ‘cubic law’ describes laminar flow behavior through smooth, parallel plates. Adjustment to the cubic law for surface roughness has been sought since the 1950s but remains elusive.

This study evaluates the feasibility of using X-ray computed tomography (CT) to measure surface roughness of natural rock fractures. Classical roughness parameters are summarized. CT and its application to imaging fracture apertures are reviewed. The CT imaging of two natural fractures is described. The resulting 3-D surface data are analyzed using conventional statistics. Power spectral density analysis using the power law method of Brown [1995] is described and performed. The issue of spatial stationarity of the surfaces is examined. The relevant concepts from fluid mechanics are summarized. The pioneering work of Lomize [1951] and Louis [1969] is reviewed. A flow test apparatus is designed and used to test a natural rock fracture. The results of 301 flow tests are summarized and analyzed. These results are compared to the roughness correction factors of Lomize [1951] and Louis [1969].

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CARBON ISOTOPE STRATIGRAPHY OF THE EAGLE FORD SHALE RELATED TO OAE II

Jeffrey Alan Thompson, B.S.

The University of Texas at Austin, 2005

Supervisor: Charles Kerans

Near the Cenomanian-Turonian boundary, a major change in oceanic circulation occurred resulting in widespread anoxic conditions in the world's oceans. This anoxic period, known as OAE 2, can be detected by a sudden increase in global δ13C values. This study found the upper limit of OAE 2 in an approximate 2‰ decrease in the δ13C values between 4.8 and 5.5m from the base of the Blue Cut Section of the Eagle Ford Shale near Moody, Texas. This value is consistent with previous studies of this kind conducted in many different areas. Previous work has described the Cenomanian-Turonian boundary as unconformable in Central Texas; however, the carbon isotope stratigraphy in this study casts doubt on that interpretation. A sedimentary analysis of this outcrop reveals that the area was frequently influenced by storm deposits and may have had a provenance in the Llano Uplift.

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BED AND FACIES SCALE SELECTIVITY DURING LATE-STAGE DOLOMITIZATION: LOWER ORDOVICIAN EL PASO GROUP, FRANKLIN MOUNTAINS, WEST TEXAS

Barbara A. Tillotson, M.S.

The University of Texas at Austin, 2003

Supervisor: Robert K. Goldhammer

Deciphering origin of dolomite and the process of dolomitization has long been an inconclusive struggle for geologists. Many different aspects of dolomitization have been applied to unraveling this puzzle, including geochemistry, sequence stratigraphy, petrography, fluid dynamics, etc. This thesis uses petrography to systematically determine a textural and allochem-specific order of dolomitization in shallow subtidal carbonate rocks from the Lower Ordovician of west Texas.

In west Texas, Lower Ordovician carbonates outcrop within the southern Franklin Mountains. These rocks display very localized dolomitization of limestone surrounding collapse breccia that formed during a large-scale (33 my) unconformity during the Middle Ordovician. The major sub-facies present in the outcrop are: (A) peloidal packstone-grainstone, (B) crinoid-intraclast grainstone, (C) sponge-spicule wackestone with wispy seams, (D) sponge wackestone-packstone with wispy seams, (E) flat-pebble conglomerate, and (F) breccia. Halos of brown fabric-destructive dolomite finger out into gray limestone, surrounding subaerial karst features within the Lower Ordovician rocks, juxtaposed below Upper Ordovician outer shelf carbonates.

Samples were collected and examined from the limestone, the dolomitization front, and the collapse breccia. Each traverse of sampling occurs over no more than ten meters. Samples were analyzed petrographically under polarized transmitted light and in cathodoluminescence. A distinct order of dolomitization was discovered from least altered to most altered rock.

The first allochems to be altered within each facies were micritized grains, intraclasts and peloids. This is due to the high amount of microporosity present within the micrite. Next, mollusks and crinoids were dolomitized. They are originally composed of aragonite and high-magnesium calcite, respectively, and have porous skeletons. These two features make them easy targets for dolomitizing fluids to attack. The last allochems to be dolomitized are the brachiopods, and trilobites and ostracods. They are composed of low-magnesium calcite and usually non-porous skeletons, providing the most stable mineral and least amount of surface area for the fluids to attack. The last to be dolomitized is the sparry/poikilotopic calcite cement, for the same reasons as the trilobites and ostracods.

The degree of alteration/dolomitization of each sample was plotted on a photomosaic of the outcrop. Based on the similar patterns of alteration, a map was made that displays gross patterns in the alteration of the rocks of the outcrop. Within the muddier beds (wackestones), there is an abrupt boundary between the dolomite and the limestone. Within the grainier beds (packstone to grainstone) there is a transitional boundary (from 5 meters to 30 meters) between dolomite and limestone.

Besides the petrographic work, a brief analysis of the fractures along the outcrop was performed to determine their influence on the dolomitization of this region. Based on the measurements taken in the field, there is no systematic pattern of fracture control as one moves away from the collapse breccia, through the dolomitized rock, into the limestone.

All of these results conclude that: 1) individual facies react differently to dolomitization depending on the allochems present and the porosity and permeability of the rock. 2) The main pathway of the dolomitization fluid into the rocks is the brecciation induced during karstification. 3) Permeability pathways for the dolomitizing fluid outside of the collapse breccia reflect facies-controlled micro-porosity. 4) The analysis of the tectonic fractures measured are not deterministic, therefore, there is no noticeable pattern of fracturing as one moves laterally away from the collapse breccia.


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KINEMATIC ANALYSIS OF OUTCROP-SCALE STRUCTURES OF THE SOUTHERN BIG SUR SEGMENT OF HIGHWAY 1, MONTEREY AND SAN LUIS OBISPO COUNTIES, CALIFORNIA

Keith Patrick Trasko, M.S. Geo. Sci.

The University of Texas at Austin , 2007

Supervisor: Mark Cloos

The Nacimiento Block is located in the Southern Coast Ranges of California , and consists mainly of Franciscan Complex accretionary prism rocks. It is cross-cut by the San Gregorio-Hosgri Fault Zone, a major right-lateral strand of the San Andreas Fault System. The Nacimiento Block is bounded on the east by the Nacimiento Fault, of debated timing and kinematics, which separates it from the Salinian Block. The Salinian Block is a piece of the Sierra Nevada Batholith, and both the Salinian and Nacimiento Blocks have been displaced from southern California by right-lateral slip on the San Andreas Fault System.

To address the question of fault kinematics, a 48 kilometer long section of the Nacimiento Block was examined along California Highway 1 between Lopez Point and Ragged Point. Exposure occurs along approximately 20 kilometers of the transect, and landsliding obscures approximately half of the exposure. The remaining 10 kilometers of outcrop were mapped. Kinematic data were taken on 29 outcrops, totaling 542 minor faults, 406 with slickenlines and 258 with sense of slip indicators, along with 314 veins. Of the faults, 202 are dip-slip (60-90° rake), 113 are oblique-slip (31-59° rake), and only 91 are strike-slip (0-30° rake). The dominant mode of minor faulting is normal, with 111 faults observed, compared to 25 reverse, 24 left-lateral, and 28 right-lateral strike-slip. Two sets of vein and one set of dike orientations were measured.

Stereographic analysis reveals the normal and reverse faults dip steeply to the southwest and strike northwest-southeast, subparallel to the coast and San Gregorio-Hosgri and Nacimiento Faults. There is no dominant orientation to the strike-slip faults. Faults of all types cut 17 slab-window related andesitic dikes, which are likely Early Miocene in age according to apatite and zircon fission track ages. The character of all fault planes is similar, indicating they are coeval.

Three stages of deformation are recognized. Subduction generated mélange, the dominant lithology in this area, and “broken formations”. A second stage of deformation is recorded in the emplacement of dikes and one set of veins. A third stage of deformation is recorded in the minor planar faults that were measured in this study. It is proposed that this latest phase of deformation is caused by the gravitational collapse of the western edge of the Santa Lucia Range . The normal faults parallel the coastline and local slope angles are up to 40°. Coeval strike-slip associated with the San Gregorio-Hosgri Fault Zone is superimposed on this deformation.

Apatite fission track ages (n=3) indicate that the dikes mapped along Highway 1 cooled to 110°C at approximately 11 Ma. This indicates an unroofing rate on the order of 300 m/my. This anomalously fast unroofing is accomplished by side-inwards gravitational collapse and erosion.

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CRANIAL OSTEOLOGY OF CAIMAN CROCODILUS AND IMPLICATIONS FOR ITS SYSTEMATIC PLACEMENT

Nina Elise Triche, B.S., B.A.

The University of Texas at Austin, 2003

Supervisor: Timothy Rowe
199 pages, 68 references

Caiman crocodilus, or the spectacled caiman, is the most common of extant caimans and has been studied by a number of renowned anatomists.  Its internal cranial morphology, however, has neither been described in great detail nor examined for phylogenetic purposes.  For example, the complexity of the pneumatic and Eustachian passages in this species may provide systematically informative data.  The ontogeny of Caiman has also not been well examined, especially not in a phylogenetic context, and knowledge of the species is thus lacking in a significant area of information.  I initiated an investigation in an effort to discover new systematic characters for C. crocodilus.

High-resolution Computed Tomography data were used to describe the osteology of Caiman crocodilus; each element of the skull was also studied for internal structures that are only visible through the use of CT.  An ontogenetic series of the species was examined, allowing description of the ontogenetic trajectory of Caiman crocodilus.  Finally, this study provides the baseline data for a re-evaluation of the systematic placement of Caiman by proposing new potential osteological and ontogenetic characters.  These include characters taken from the  morphology of the pneumatic and eustachian passages and from ontogenetic data.

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SYSTEMATICS, BIOGEOGRAPHY, AND EVOLUTIONARY HISTORY OF FOSSIL AND EXTANT PENGUINS (AVES: SPHENISCIFORMES)

Nina Elise Triche, Ph.D.

The University of Texas at Austin , 2007

Supervisor: Timothy B. Rowe

The excellent penguin fossil record is temporally long, among the oldest of modern birds, and contains fossils on every Gondwanan continent except India . However, most of fifty-nine named taxa are isolated skeletal elements, many of which are non-comparable. Fossil diversity is highest in New Zealand , with additional Antarctic and Patagonian faunas and fewer remains from Australia and South Africa . Phylogenetic hypotheses place penguins within Aves and Neornithes, but further relationships remain contentious. Recent work clarified living species' phylogeny, but none examined all fossil taxa.

I describe penguin skeletal anatomy using CT scans and museum specimens, providing the first such description for all living and extinct species in an explicitly phylogenetic framework. All elements are phylogenetically variable, i ntergeneric variation is large, and extinct taxa are more variable than extant. I recommend that future systematic works include all elements for extinct species diagnoses, osteology for living species, and discussions of intraspecific variation. This description grounds my phylogenetic analysis, based on a 503-character matrix of osteological, myological, integumentary, and behavioral characters. This greatly expands previous datasets, and allows recovery of a highly resolved phylogeny, including monophyly of two extinct clades and the crown-group. Data partitions support different levels of relationship, whereas missing data and outgroup choice drastically affect recovered topology. Incorporating the maximum amount of data gives the highest resolution by recovering all relevant character states. I propose the first formal phylogenetic nomenclature for sphenisciforms, and define and diagnose previously used terms such as Panspheniscidae (total group), Sphenisciformes (known penguins), Spheniscidae (crown-group), Palaeeudyptidae and Paraptenodytidae (two extinct clades). I coin Spheniscoidea (Spheniscidae + Paraptenodytidae) and Australodyptinae ( Aptenodytes + Pygoscelis ).

After calibration with geologic time, I calculate the completeness of the pencuin record and determine confidence intervals to estimate a Cretaceous origin and an Eocene crown-clade origin. These dates and the derived phylogenetic placement of penguins suggest that numerous extant bird lineages may also have Cretaceous origins. I recover a New Zealand origin for penguins and a West Antarctic origin for the crown-group and extinct clades. Correlating penguins with tectonic and climatic data indicates an Eocene adaptive radiation, probably related to latest-stage Gondwanan breakup and associated global cooling.

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THE DETRITAL ZIRCON GEOCHRONOLOGY AND STRUCTURAL PETROLOGY OF PACHECO PASS, DIABLO RANGE, CENTRAL CALIFORNIA: IMPLICATIONS FOR SUBDUCTION ZONE TIMING AND TECTONICS

Alka Kumari Tripathy, M.S. Geo. Sci.

The University of Texas at Austin , 2006

Supervisor: Mark Cloos

The timing and tectonic history of blueschist facies rocks, though a widely studied problem, is still a topic of considerable debate because of limited age constraints in terranes with few fossils or marker beds. This study applies U-Pb detrital zircon geochronology by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), to a well-studied blueschist facies terrane, the area around Pacheco Pass , in the Diablo Range of central California . This window through the Great Valley forearc basin deposits consists of the deepest coherent parts of the Franciscan accretionary complex that are exposed. 150 zircon grains were analyzed from each of sixteen samples, to determine their U-Pb ages. Additionally, a mineralogical and microstructural study of 103 thin sections was performed by traditional optical microscopy to supplement the geochronologic information.

The maximum ages of deposition for coherent metagraywackes are as young as ca. 90 Ma, and ca. 70 Ma for blocks in mélange. Using the observed age distribution, the coherent rocks are divided into two units: Unit 2 (unimodal) and Unit 3 (bimodal). Unit 2 is structurally higher than Unit 3; thus, it was underplated first.

Similar patterns are present in the Sacramento Valley of the Great Valley forearc basin (DeGraaff-Surpless et al., 2002), except that the base of the section is unimodal, and the upper parts are bimodal. This evolution is thought to reflect increased dissection of the arc over time due to the eastward stepping of the drainage divide. The source area for the coherent units is inferred to be similar to that of the Great Valley Group: the Sierran magmatic arc and associated terranes in northern California , western Nevada and southern Oregon .

To explain the geochronology, as well as field observations, underplating must occur at the tens-of-meter scale, although larger or smaller packages of rocks are not precluded. Minimum rates of underplating, based on the maximum ages of deposition for the two coherent units, are 10 to 30 m/m.y.

The layer-parallel foliation is defined by sheet silicates and pressure solution selvages, with sodic amphibole, lawsonite and blocky jadeitic pyroxene parallel to it. Shear strain from subduction tectonism before and after underplating was not thoroughly penetrative to the ten-meter scale, but the S 0 /S 1 foliation formed during this part of the history of these rocks. In the phyllites, cm-scale isoclinal folds and layer-parallel veins that have quartz fibers subparallel to the vein margin are also present.

Near-static conditions were reached when continued underplating sequestered earlier accreted rocks from the subduction channel. Radiating sprays of jadeitic pyroxene and unoriented lawsonite tablets formed at this time, concurrent with the opening of anisotropy-controlled layer-parallel veins.

Mélange genesis began after 90 Ma, and was active by at least 70 Ma, which corresponds to the onset of Laramide style orogenesis in western North America . By 60 Ma, however, the rocks were at 110°C, based on apatite fission track data, which corresponds to a depth of ~15 km, with geothermal gradients of 10°C/km. This indicates rates of unroofing of 500 m/m.y. from depths of ~30 km.

Localized folding and simple shear in an extensional regime is characteristic of this latter phase of deformation. Folds with axial planar pressure solution cleavages that are superposed upon one another indicate localized zones of sinistral shear in near-vertical shear zones. Ptygmatically folded veins have been shortened up to 70% in some cases. Pressure solution has removed up to 30% of the rock volume in some cases.

When the rocks moved out of the regime of ductile deformation, layer-perpendicular veins and post-foliation faults formed. Some of the unroofing, therefore, was accommodated by faulting in the latter part of the unroofing history.

The Quien Sabe volcanic rocks (11-9 Ma) overlay Franciscan rocks of the Diablo Range . Hence, these blueschists must have been at the surface by ~10 Ma. Therefore, the minimum rate of unroofing between 60-10 Ma is 300 m/m.y. This indicates slow synsubduction unroofing.

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RESERVOIR CHARACTERIZATION, PALEOGEOMORPHOTOGY, AND GENESIS OF THE MISSISSIPPIAN REDWALL LIMESTONE PALEOKARST, HUALAPAI INDIAN RESERVATION, GRAND CANYON AREA, ARIZONA, U.S.A.

Tony John Troutman, M.S. Geo. Sci.

The University of Texas at Austin, 2004

Supervisor: William Fisher

221 pages, 86 references, 12 plates

The Mississippian Redwall Limestone paleokarst in the western Grand Canyon area provides and excellent outcrop analog for understanding paleokarst in three dimensions. Major controlling factors in the formation of this paleokarst include exposure time, tectonic and eustatic events, paleohydrology, and paleoclimate. The Redwall paleokarst shows examples of polyphase development, with earlier cave systems exerting strong influence on the formation of later phases ofkarstification. A close association of the paleokarst with the Surprise Canyon Formation paleochannels was found, suggesting these channels formed local base level and outlets for the

paleocave drainage. Parts of the paleocave system show evidence of a phreatic phase of speleogenesis, with evidence of relict flowstone and bedded fluvial sediments in the base of the collapse breccia. Parts of the breccia bodies show strong correlation to a fracture set that is found only in Missssippian strata, suggesting that fractures were a control on speleogenesis and paleocave system morphology. No breccia bodies were found that penetrated deeper than the chert beds of the Thunder Springs Member. These chert beds likely formed a paleohydrologic barrier that limited the depth of karstification. Very little evidence ofpaleosols or other clues to paleoclimate could be found, demonstrating that this may be one of the most difficult factors to understand. There is evidence that the paleokarst, combined with the paleochannels of the Surprise Canyon Formation once formed a well-connected but geometrically complex aquifer or potential reservoir. The Redwall paleokarst presently has little porosity and is acting as a flow barrier, but it retains open fracture porosity in outer parts of the collapse beds surrounding the paleokarst breccia bodies. This open fracture porosity appears to be contributing to the formation of later phases of karstification. A hypothetical model of the paleocave distribution is developed using evidence of fracture control, base level control, and paleohydrology to constrain the style of paleocave morphology.

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RETROGRADATION OF THE PLIOCENE GLOBOQUADRINA ALTISPIRA SHELF MARGIN, NORTHERN GULF OF MEXICO

Eric Tuitjer, M.S. Geo. Sci.

The University of Texas at Austin, 2003

Supervisor: William E. Galloway

93 pages, 34 references, 23 plates

The Pliocene depositional episode (depisode) of the northern Gulf of Mexico records a significant landward migration of the shelf margin. Onset of retrogradation is marked by the Buliminella 1 (PB1) flooding event and continues to the Globoquadrina altospira (PGa) flooding event. An intermediary flooding event ( Globorotalia margaritae (PGm)) subdivides the Pliocene into an upper and a lower depisode. Shelf margin retreat is recorded by incremental changes of: i) shelf margin location, ii) sediment accumulation thicknesses, iii) depositional styles, and iv) paleobathymetry. Two major shelf margin depocenters existed throughout both depisodes. These depocenters are growth-faulted and sourced by deltas that migrated across the shelf. Sediment loading and the directly-related salt evacuation created instability that lead to the repeated catastrophic failure of the shelf margin delta complexes and the subsequent routing of sediments onto the slope and basin floor. Salt mobilization during this time emplaced salt sheets at shallow depths within the slope (McBride, 1998). Minor topography generated by salt tectonics preferentially routed and trapped sediment within the slope. The reciprocal response of slope deposition and salt evacuation led to the development of thick intra-slope minibasins. Subsequent fill-and-spill allowed for sediment bypass and the development of an extensive basin floor fan.

While experiencing similar time spans of deposition, the lower Pliocene depisode accumulated greater sediment thicknesses at the shelf margin and within the slope but a less-extensive fan. Shelf margin retreat was more pronounced at this time and broad delta- and slope-fed aprons marked slope deposition. Subsequent avulsion of the Mississippi River and a significant regression starved the upper Pliocene depisode of sediments on the shelf, margin and slope. Depositional aprons on the slope became narrower and display retrogradational accumulation. Infilling of intraslope minibasins during the previous sub-sequence permitted efficient sediment bypass and resulted in the deposition of a much more extensive basin floor fan.

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ANATOMY, ONTOGENY, AND PHYLOGENY OF COELOPHYSOID THEROPODS

Ronald Stephen Tykoski, Ph.D.

The University of Texas at Austin, 2005

Supervisor: Timothy Rowe

Coelophysoid theropods (Dinosauria: Saurischia) were viewed as members of Ceratosauria in early cladistic phylogenetic hypotheses, but more recent analyses placed Coelophysoidea and Dilophosaurus as successively closer outgroups to Neotheropoda (Ceratosauria + Tetanurae). Most cladistic studies did not appreciate the importance of relative maturity to the expression of some characters in coelophysoids. Often the role played by ontogenetic variation was not considered, or maturity-dependent characters were deleted from analyses. I used cladistic techniques to derive a hierarchy of relative maturity and map the sequence of ontogenetic transformations among coelophysoid specimens. I then conducted an extensive phylogenetic analysis of basal theropod relationships. Taxa and characters used in the phylogenetic analysis were examined in detail. Separate phylogenetic tests were run to evaluate different approaches to dealing with the relative maturity of specimens in cladistic analyses. The first test coded characters as if all taxa were represented by adults, and resulted in a taxon known only from immature specimens being placed in a basal position. The second test removed maturity-dependent characters from consideration, and resulted in Coelophysoidea being placed outside Ceratosauria, basal to Neotheropoda. The third test incorporated the results of the ontogenetic analysis. Maturity-dependent characters were coded as 'missing data' instead of 'absent' in taxa represented by immature specimens if the ontogenetic analysis showed the derived states of characters were expressed only at stages of maturity more advanced than the representative specimens. The third test resulted in Coelophysoidea being placed as the sister lineage to Ceratosauroidea within Ceratosauria. My study shows that the approach used to deal with ontogenetic variation in fossil taxa can alter the outcome of phylogenetic analyses. The use of a quantitative ontogenetic analysis to determine the relative maturity of fossil specimens, the subsequent approach to coding maturity-dependent characters for taxa represented by immature specimens, and the addition of new anatomical data all contributed to more robust hypotheses of relationships among basal Theropoda.

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PROCESSES AND ARCHITECTURES OF DELTAS IN SHELF-BREAK AND RAMP PLATFORMS: EXAMPLES FROM THE EOCENE OF WEST SPITSBERGEN (NORWAY), THE PLIOCENE PALEO-ORINOCO DELTA (SE TRINIDAD), AND THE CRETACEOUS WESTERN INTERIOR SEAWAY (S WYOMING & NE UTAH)

Carlos Alberto Uroza, PhD

The University of Texas at Austin, 2008

Supervisor: Ronald J. Steel

This research investigates different scenarios of deltaic deposition, both in shelf-break and ramp settings. I address four ancient cases with particular characteristics: 1) A shelf-margin case from the Eocene Battfjellet Formation, West Spitsbergen, Norway, in which deltas were able to migrate to the shelf-edge during rising and sea-level highstand conditions despite the low-supply character of the system (low progradation/aggradation rates compared to analogous margins), with consequent sand starvation on the slope and deeper areas of the basin. The delta system was overall wave-dominated, with restricted tide-influence at the mouth of the distributaries and more accentuated tide-influence during the transgressive transit of the deltas; 2) A shelf-margin case from the Pliocene paleo-Orinoco Delta System, Mayaro Formation, SE-Trinidad, in which high rates of sediment supply from the paleo-Orinoco River and exceptionally high subsidence rates due to growth-faulting, produced a spectacular stacking of sandstones on the outer shelf and shelf-edge areas, but with apparently limited sand delivery into deeper waters. The delta system was overall storm-wave dominated, with fluvial-influence in the lower segment of the system and some tide-influence in association with the fluvial-influence; 3) A case from a shallow-water ramp, Campanian Rock Springs Formation (Western Interior Seaway), in which deltas accumulated along relatively straight, north-south oriented shorelines highly impacted by wave-storm processes. Tide-influence was limited to the mouth of the distributaries, and fluvial deposits mostly developed within the coastal-plain areas; and 4) A case from the same ramp setting as (3) but in an outer-ramp site, Campanian Haystack Mountains Formation, in which a lowering in sea-level translated the delta system tens of kilometers eastwards into the basin. As a consequence of a shallower and narrower seaway, southerly-oriented tidal currents were enhanced and subsequently skewed or re-aligned the delta system to the south.

The key contributions of this research concern (1) the feasibility of shelf-margin accretion during rising and highstand of sea level, (2) the critical importance of shelf width and sediment supply (and not only sea-level behavior) to bring deltas to the shelf-edge, and (3) the possible tendency for tides enhancement in the distal reaches of shallow seaway ramps, caused by narrowing of the seaway and fault-topography enhancement during falling sea level.

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FORMATION AND ORGANIZATION OF AEOLIAN BEDFORMS

Daniel Shane Valentine, M.S. Geo. Sci.

The University of Texas at Austin, 2004

Supervisor: Gary Kocurek

92 pages, 60 references

Aeolian bedforms represent some of the most intricate land forms on the planet encompassing a variety of scales from wind ripples on the order of centimeters to desert sand seas comprising thousands of square kilometers. Hypotheses focusing on the formation and organization of these bedforms have been nearly as complex and varied as the dunes themselves. Three distinct topics were chosen for the focus of this study: (1) the formation and organization of wind ripples; (2) morphology and sampling effects from measurement of dune lee side airflow; and (3) the formation of star dunes based on wind tunnel studies of small scale star ripples. Each of these topics comprises a chapter of this thesis, which will be published individually at a later date.

Wind ripple formation has been a topic of discussion for nearly a century. For this study ripples were formed in a wind tunnel and recorded using time-lapse photography. Data reveal that ripples form in a pattern that closely matches the formation of computer simulated bedforms using only basic rules of sand transport, but neglecting any sort of aerodynamic control of bedform morphology. These findings support the hypothesis that aeolian bedforms are self-organizing and that no predisposed template of formation exists within the fluid flow.

Aeolian dune lee side airflow comprises a complex subject of study. The airflow is the result of a complex interaction between the wind and the sand surface. Using a new technique of wind velocity data collection, a more accurate picture of the lee side airflow morphology is now available. This data set provides the most comprehensive look at this environment to date. Of particular interest are the data outlining the Internal Boundary Layer, which is closest to the sediment surface and controls sediment transport. The data collected imply that no point of dune nucleation, caused by a drop in shear velocity, exists in the interdune corridor, rather, the shear increases downwind until another dune is reached. Conclusions based on the data support the theory of self-organization when applied to desert dunes.

Star dunes are the largest and most complex single bedforms found on Earth. Due to their size and long development time, observations of star dune formation are scant. Using a rotating table mounted in a wind tunnel, a series of complex wind patterns were simulated. Small scale star ripples were formed and the process recorded using time-lapse photography. Based on these findings at least two distinct types of star dunes are possible in nature. Because of the relationship between the wind regime and the bedforms produced, a causal link between aerodynamic control and bedform formation is dubious. More likely, however, is the self-organization theory, which has proven useful in all scales of bedforms examined in this study.


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STRATIGRAPHIC RELATIONSHIPS BETWEEN THE WEBER SANDSTONE AND THE MAROON FORMATION IN THE RANGELY FIELD, NORTHWESTERN COLORADO, U.S.A.

Diego J. van Berkel, Geol. Engineer

The University of Texas at Austin , 2006

Supervisor: William Fisher & Kitty Milliken

The study of interbedded eolian and fluvial deposits, their inherent heterogeneities, and the impact on reservoir quality are the main subject of this research. The analysis of more than 2000 feet of core from four wells along with petrophysical data from 50 wells in the Rangely oil field, northwestern Colorado , allowed the characterization of textural and diagenetic parameters which ultimately control the reservoir quality.

Compositional and compactional parameters were determined for the reservoir lithologies of both facies. Dune deposits lithology include subarkosic sandstones, arkose and lithic arkose sandstones. They have an architectural assemblage of F 70 M 1 C 17 P 12 and major grain ratios of Q 77 F 16 R 7 . Fluvial channel deposits show an assemblage of F 79 M 3 C 1 4P 4 with a major grain ratio of Q 64 F 23 R 13.

Textural and compositional parameters clearly show that eolian dune sandstones are more mature texturally than their fluvial counterparts. These textural differences influenced the path of porosity loss processes and controlled the performance and quality of the reservoir. Quantification of compactional parameters as Intergranular Volume (IGV), Compactional Porosity Loss (COPL), Cementational Porosity Loss (CEPL) and Index of Compaction (Icomp) enable the determination of the best reservoir facies. IGV values for eolian dune deposits average 26.7%, with COPL and CEPL averaging 24.8%, 11.1% and 0.69, respectively. Sand sheet sandstones show average values of 25.4%, 26% and 14% with an Index of Compaction (Icomp) in the order of 0.6

Average values for fluvial deposits regarding the same porosity loss and compactional parameters result in an IGV=16.8%, COPL=33.3%, CEPL=9.4 and Icomp=0.8

The vertical pattern and relative proportions of eolian and fluvial facies allowed the subdivision in two intervals designated informally as Upper and Lower Weber.

At a reservoir scale the thickness and spatial distribution of contrasting eolian and fluvial textures as well as their locally relative proportions ultimately determined the zones of better quality in the area of Rangely Field. A steady thickening trend of eolian deposits is observed in the informal Upper Weber. Conversely, a thinning and regular thinning trend is apparent in fluvial facies. Lack of data in the north and northwestern zones prevented a determination of spatial trends for the Lower Weber.

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RECHARGE IN A SEMI-ARID BASIN AQUIFER: RYAN FLAT AND LOBO FLAT, TRANS-PECOS, TEXAS

Norman G. Van Broekhoven, M.S. Geo. Sci.

The University of Texas at Austin, 2001

Supervisor: John M. Sharp

In arid and semi-arid settings a key hydrological question is: does significant recharge occur and, if so, where, how much, and by what mechanisms? Ryan Flat and Lobo Flat are underlain by a bolson aquifer in Trans-Pecos Texas where the groundwater recharge is generally accepted to be slight. Previous studies suggest that recharge by direct infiltration into the basin fill and typical ephemeral streams in the basins is, at most, a few mm/yr. Evapotranspiration and the soil texture restricts infiltration and recharge. Nor were alluvial fans near the study aquifer usually found to be the sites of recent recharge. Infiltration into these fans appears to be impeded by low permeability layers deposited by sheet flow. Yet recharge occurs in portions of the aquifer underlying Ryan Flat and Lobo Flat. Recent recharge is suggested by groundwater potentiometric mounds centered about VH Canyon to the west and along the front of the Davis Mountains to the east. Groundwater from the mountains and these mounds have a different chemical facies than groundwater down gradient and are hypothesized to be younger members of a continuous chemical evolutionary trend. This infers that the central basin water originated in the mountains and basin margins.

Groundwater isotopic data indicate that recharge is not subject to extensive evapotranspiration as occurs in the thick unsaturated zone of the basin fill. This supports the hypothesis that recharge occurs by rapid infiltration at select locations such as mountain fractures, basin margins, or ephemeral streams. Geophysical methods were used to investigate infiltration in the ephemeral stream channel near VH Canyon. Direct observations of rain events, stream flow, and infiltration provide supporting evidence that this is a site of preferential infiltration and recharge.

Field mapping of fractures in mountain canyons, analysis of digital elevation models and aerial photographs indicate that the position of the mountain canyons and streams are controlled by fractures. The mechanisms of recharge seem to be a combination of fracture infiltration and flow in the mountains, infiltration into the bottoms of ephemeral streams in mountain canyons that are located along fracture zones, and infiltration of ephemeral streams near the basin margin. Digital elevation models (DEMs) were proven to be useful for identifying topographic linears caused by fractures in the mountains and under the basin fill. DEMs were able to enhance topographic trends that were less evident in aerial photographs having a much higher resolution.

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ANALYZING PRIVATE PARTICIPATION AND THE ECONOMIC IMPACT ON THE GAS TRANSMISSION INDUSTRY: A GLOBAL OVERVIEW

Gina Luz Vega Riveros, M.A.

The University of Texas at Austin, 2003

Supervisor: Willem C.J. van Rensburg

Countries in Asia, Europe, and North and South America are introducing reforms to boost efficiency and attract new private investment in their natural gas industries. The trend has been to unbundle along vertical and horizontal lines and to open wholesale gas markets to new entrants. These new entrants stimulate competition and the development of new markets in gas supply, in financial gas contracts, and in pipeline capacity. Different kinds of alliances and joint ventures are observed in the gas markets during the past few years. Russia is very aggressively privatizing the gas market. Therefore, private gas transmission is expanding in the market and this trend will continue accelerating in the next few years.

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SUBSURFACE STRUCTURE, STRATIGRAPHY, AND REGIONAL TECTONIC CONTROLS OF THE GUAJIRA MARGIN OF NORTHERN COLOMBIA

Eleine Melisa Vence, M.S. Geo. Sci.

The University of Texas at Austin, 2008

Supervisor: Paul Mann

128 pages, 94 references, 2 tables

I combine previous data from Mesozoic outcrops in the Guajira Peninsula of northern Colombia with new regional gravity, bathymetric, and seismic interpretations to demonstrate the existence of a 280-km-long, western extension of the Great Arc of the Caribbean (GAC) along the continental margin of Colombia. Seismic data reveal a 80 to 100 km-wide domal-shape basement high lacking seismic reflectivity and mappable for 1800 km from the Aves Ridge to the study area in offshore Colombia. The western extension of the GAC in Colombia and western Venezuela is buried by 700 to 3000 m of continental margin sediments because it collided earlier (Cretaceous-early Paleogene collision) than its subaerially exposed eastern part on the Leeward Antilles Ridge (late Paleogene-Neogene collision). Compilation of radiometric age dates and geologic information from the entire GAC shows that arc magmatism ocurred from 128 to 74 Ma with a general pattern of younging from west to east.

I mapped six Upper Eocene to Recent marine seismic sequences that overlie the domal basement high of the GAC using 2400 km of seismic reflection data and 12 wells. Three deformation events affecting the sequences include: 1) late Eocene rifting, in an east-west direction produced half-grabens in the northern part of the area; 2) Oligocene transtension, in the southern part of the area expressed by right-lateral Oligocene strike-slip faulting and extensional basin formation; 2) early – middle Miocene transtension; and 3) late Miocene – early Pliocene Andean uplift and clastic infilling of offshore basins.

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3-D SEISMIC GEOMORPHOLOGY: INTEGRATING WELL LOG AND STRATAL SLICE DATA, WEST NATUNA BASIN, INDONESIA

Judson Bryan Walker, MS GeoSci

The University of Texas at Austin, 2003

Supervisor: William Galloway

104 pages, 37 references

Three-dimensional (3-D) seismic geomorphology provides an indication of a reservoir's internal and external architecture. This furthers an understanding of depositional processes and allows a prediction of fluid flow during hydrocarbon production. The West Natuna Basin, located in the Gulf of Thailand, is a productive, gas prone Cenozoic basin. Exploitation of gas reserves has been greatly aided by 3-D seismic surveys. In particular, the Belanak field, discovered in 1975, provides a large reserve base for the Singapore gas market.

High resolution seismic provided by ConocoPhillips reveals detailed fluvial, deltaic, and shallow marine architecture associated with the dominantly Miocene aged sediment. An analysis of stratal slice data over a 2000 millisecond interval formed the basis for a comprehensive sequence stratigraphic framework and system evolution. Gamma ray well log data from seven wells inside the Belanak field were integrated with the stratal slice data to provide a more robust and accurate geologic model. This integration tied morphological features seen in the stratal slices with distinct log facies. The sequence stratigraphic model presented is thus a marriage between more traditional log analysis techniques and the more novel study of geomorphic elements observed in the stratal slice volume.

The resultant 39 high-frequency systems tracts record a consistent pattern of highstand tide-dominated deltas followed by unicised lowstand bypass channels capped by marine transgressive muds. Dominant channel orientation trends northwest to southeast and is controlled by the active compression and rotation of Indochina into the Asian landmass. A secondary channel orientation, from southwest to northeast, manifests itself during TimesNewRoman of tectonic quiescence.

Though the ultimate effectiveness of integrating well log data and high resolution 3-D stratal slices is dependant on several factors such as resolution of the seismic and the probability of well log/morphological feature intersection its utility is undeniable for hydrocarbon exploration and production. In particular:

  1. More accurate sequence stratigraphic models can be generated by supplementing well log data and conventional seismic interpretation with stratal slice analysis.

  2. A better understanding of sediment source, transport, and deposition can be obtained.

  3. Reservoir distribution, laterally and temporally, can be described and quantified with increasing confidence and accuracy.

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THE GEOCHEMICAL BEHAVIOR AND TRANSPORT CHARACTERISTICS OF ESTROGENS

Tania Clare Wallace, M.S. Geo. Sci.

The University of Texas at Austin, 2004

Supervisor: Philip C. Bennett

111 pages, 77 references

Hidden text: The abstract may be included at the discretion of the Supervisor.

Estrogens are prevalent anthropogenic inputs to our environment because of their specific medical usage (i.e., sources from birth control pills, estrogen replacement therapy, livestock farming, etc.), inactive nature upon excretion, unique physicochemical properties (site specific receptor binding, moderately hydrophobic), and reactivation during sewage treatment processes. This study characterizes the behavior of natural estrogens discharging from local waste water treatment plants (WWTP) in Austin, where karst features play a critical role in the local hydrogeology.

Laboratory analyses using a high pressure liquid chromatography (HPLC), was used to measure the estrogen concentrations in soils and water. Batch sorption experiments were used to calculate sorption coefficients (K d) of estrogen to Walnut Creek sediment. The K d values measured are 2.14 x10 4 Lkg -1 for 17β-Estradiol, 1.88 x10 3 Lkg -1 for Estriol, and 2.53 x10 4 Lkg -1 for Estrone; this indicates that this clay-rich sediment would sorb estrogen discharged from the Walnut Creek WWTP. Experiments also show that natural estrogens re-equilibrate from the sediment to the liquid phase.

Because predicted concentrations of estrogen in the environment are at much lower concentrations, water samples from WWTP’s were analyzed using an enzyme-linked immunosorbent assay kit (ELISA). The natural estrogen, 17β-Estradiol, was detected at Walnut Creek and Govalle WWTPs. Overall, the autumn concentrations were greater than spring concentrations, and varied from 30 to 700 ppt in the treatment processes.

Once discharged into the aquatic environment, estrogens are subjected to other processes, including photodegradation, microbial degradation, and transport. Estrogens will absorb ultraviolet light strongly and moderately in the visible light range, resulting in photodegradation almost 4 times as fast at UV wavelengths. These endocrine disrupting compounds may become bioavailable downstream of WWTP by sorption onto colloid particles, especially with high organic carbon content. Estriol and 17B-Estradiol are mobile in porous media with low organic carbon content. The retardation coefficients are 1.1, whereas Estrone has greater retardation at 1.36. These geochemical parameters and others were summarized for use in a fate and transport modeling of estrogen in the natural environment.


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VELOCITY ESTIMATION FROM SEISMIC DATA BY NONLINEAR INVERSION AND CHARACTERIZATION OF GAS HYDRATE DEPOSITS OFFSHORE OREGON

Chengshu Wang, Ph.D.

The University of Texas at Austin, 2003

Supervisors: Mrinal K. Sen and Robert H. Tatham

145 pages, 121 references

Seismic attributes such as travel and reflection amplitude variation with offset contain information on the elastic parameters of subsurface rocks. The aim of generalized inversion of seismic data is to estimate values of the elastic parameters such as P-wave velocity, S-wave velocity and density for lithology discrimination and direct detection of hydrocarbons. My dissertation research comprises two parts: development of a method to improve the least-squares and the preconditioned conjugate gradient algorithm, and estimation of detailed velocity structure of gas hydrate-bearing sediments offshore Oregon from Ocean-bottom seismometers (OBS) and multi-channel streamer (MCS) data.

I developed a new nonlinear inversion algorithm for estimating velocities from fully stacked reflection data with application to a field data set consisting of well logs from Ocean Drilling Program (ODP) Leg 170 and multi-channel seismic reflection (MCS) data offshore Costa Rica. Inversion of post-stack seismic data generally yields reflection coefficients or impedance as a function of two-way reflection time. In this experiment, fully stacked seismic data and density logs at selected locations along a 2-D seismic line are inverted to estimate seismic velocities. Mathematically, generalized inversion provides the best estimate of earth model parameters by minimizing the so-called cost (or misfit between observed and computed seismic data) function, which is a function of the data covariance matrix CD and the a priori model covariance matrix CM. Matrices CD and CM (generally approximated by scalars ód and óm) introduce stability to the process and robustness and thus have strong influence on the quality of the final inversion solution. Based on the least-squares and the preconditioned conjugate gradient algorithm, I have developed a 2-step procedure to solve this nonlinear inverse problem by first determining the two matrices CD and CM using the two-step procedure that involves mapping the sensitivity of model smoothness and data error to the parameters ód and óm .I found that there always exits an area in the dm plane in which the low values of the cost function lie, and hence a large 2-dimensioanl search space can be reduced to a significantly smaller search region. This led to the easy application of this method.

The results from this experiment show that almost every identified reflector of seismic data is very well matched by final synthetic seismograms and the density from borehole log data, which confirms that my estimates of velocities are reliable. Combination of the inverted velocity and density profiles allows identification of major stratigraphic boundaries.

The improved inversion method is extended to the inversion of pre-stack seismic data, which is applied to estimate seismic velocities of gas hydrate-bearing sediments, offshore Oregon. Gas hydrates are recognized as a target for major future energy reserves, are believed to be a potential source of an important greenhouse gas, and are considered to be a possible cause of submarine geo-hazard. A simple indicator of gas hydrate is a bottom-simulating reflector (BSR), which marks the transition between hydrate-bearing sediments with high Vp above free gas with low Vp. A 3-D streamer and ocean bottom seismometer (OBS) survey in the Hydrate Ridge, offshore Oregon was conducted to image structures controlling the migration of methane-rich fluid and free gas and to map the gas-hydrate distribution. Preliminary Vp and Vs profiles obtained from OBS data by interactive analysis are used as a starting model to estimate Vp from the streamer data.

The results of my inversion and interpretation study in Hydrate Ridge are summarized below:

Both 3-D streamer and OBS data show a strong BSR indicating the presence of gas hydrate above and free gas below.

Interactive P- and S-wave velocity analysis of OBS data allows us to identify the presence of a "conversion surface" in the gas hydrate-bearing sediments. The conversion surface separates the overlying low P-wave velocity layer and underlying high P-wave velocity layer.

Inverted velocity profiles show a low-velocity layer existing below the sea floor and above the normal gas hydrate, suggesting a new geological model of gas hydrates.

Two types of hydrate fabrics, massive and porous hydrates, observed by deep-towed video survey, were identified in the P-wave velocity profiles. Three main layers of gas hydrate-sediments separated by the conversion surface and BSR are distinguished. Below the free gas is the normal sedimentary section.

The profiles reflecting the physical properties of sediments, such as the P-wave velocity, acoustic impedance and Poisson's ratio profiles, are able to map the distribution of gas hydrates and show very similar trends of lateral variation of the main layers.

A series of faults in the accretionary complex under the ridge not only offer pathways for methane and fluid ascending from deeper layers but also control the distribution of the porous hydrates with low velocity below the seafloor.

Hornbach et al. (2003) suggest their results using velocity analysis of seismic reflection data on the Blake Ridge is the first direct seismic detection of concentrated hydrate confirmed by velocity analysis. My results of direct inversion of seismic data extend these results to greater resolution of the entire seismic data set. Further, my results may be the first seismic indication of a visually observed porous hydrate zone.


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OPENING HISTORY AND POROSITY EVOLUTION OF FRACTURES IN SANDSTONE, TRIASSIC TO JURASSIC LA BOCA FORMATION, NORTHEAST MEXICO

Meghan Elizabeth Ward, M.S. Geo Sci

The University of Texas at Austin , 2006

Supervisor: Stephen E. Laubach

Sandstone outcrops of the Triassic to Lower Jurassic La Boca Formation, NE Mexico , offer an unusually well preserved example of cements within opening-mode fractures (veins and joints). Although all fractures in these outcrops that can be reliably attributed to subsurface deformation contain cements, some retain open pore space whereas others have been sealed. Quartz cement within otherwise open fractures contains crack-seal textures that record fracture opening history. Elsewhere otherwise identical fractures are sealed with calcite. Outcrops contain fractures that range over three orders of magnitude in size quantified by kinematic aperture. Kinematic apertures of sealed microfractures and open and sealed macrofractures have distributions that can be described by power law scaling. Fracture size and cements deposited during and after fracture opening govern fracture porosity evolution. Although similar patterns have been found in many cored fractures from low-porosity sandstones, my study is the first to document these patterns in outcrop.

I used aperture measurements along scanlines, petrography, fluid-inclusion analysis and high-resolution scanning electron microscope-based cathodoluminescence (CL) mosaics to characterize cement and fracture populations. CL imaging of quartz cement reveals crack-seal textures that show cement precipitation while fractures were opening. Using recent cement precipitation models and maps of cement deposit patterns within crack-seal cement bridges, I infer that cement deposition proceeded at rates comparable to overall fracture pattern formation but slower than individual cracking episodes. My observations are consistent with a model of quartz precipitation in fractures proposed by Lander et al. (2002) in which thermal exposure history and rock surface area govern cement accumulation rate and patterns.

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SALT TECTONICS, SEDIMENTATION, AND BASIN DEVELOPMENT IN SAFI HAUTE MER, OFFSHORE MOROCCO

Chad Matthew Weisenburger, M.S. Geo. Sci.

The University of Texas at Austin , 2007

Supervisor: Lesli J. Wood

An extensive 3-D seismic volume covering an area of 1064 km 2 has been used to analyze the morphology of the lower continental slope, determine the emplacement history of allochthonous salt structures, and to examine the temporal changes in the interaction of structure and sedimentation in offshore Morocco . The survey area is located roughly 150 km west of the Moroccan coast, in Safi Haute Mer permit area, in a water depth of approximately 2000 meters. The western half of the survey lies just outside of the salt basin and is marked by relatively flat-lying strata. The eastern half of the survey lies within the salt basin and is characterized by sedimentation around salt structures and deformation of salt and sediment. At the distal edge of the salt basin, a thin salt sheet has been driven by sediment loading to extrude at least 10 km beyond the salt basin's western depositional edge.

A series of structural restorations show changes in salt structure growth through time. Interval isopach maps allow examination of spatial and temporal changes in depocenters and assessment of the influence of salt mobilization on basin fill pattern. In the study area, Late-Triassic to Early-Jurassic age salt is believed to have become mobilized in the Jurassic, resulting in a number of different types of halokinetic structures including diapirs, salt sheets, salt-cored anticlines, and turtle structures. Structure development has been dominated by a combination of several tectonic processes at any given time throughout the evolution of the margin. Up to 6000 meters of sediments have been deposited in basins created by salt evacuation and around paleo-highs cored by mobile salt since Early Jurassic time. DSDP data from the deep offshore shows the Early-Jurassic to Early-Cretaceous strata to be carbonates, while the strata younger than Early Cretaceous are dominantly siliciclastic. The Moroccan continental margin has developed from a complex interaction of sediment and salt, resulting in a variety of structures attractive to hydrocarbon exploration.

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FROM SEAFLOOR SPREADING TO UPLIFT: THE STRUCTURAL AND GEOCHEMICAL EVOLUTION OF MACQUARIE ISLAND ON THE AUSTRALIAN-PACIFIC PLATE BOUNDARY

Karah Lynn Wertz, Ph.D.

The University of Texas at Austin, 2003

Supervisor: Sharon Mosher

169 pages, 146 references, 2 plates

Macquarie Island (54º30'S, 158º54'E) is unique, consisting of a section of uplifted oceanic crust and upper mantle that still lies within the ocean basin where it formed. Earlier geophysical studies indicate that between ~40 and 6 Ma, this plate boundary evolved from a spreading ridge to the modern transpressional boundary. The rocks of Macquarie Island record both regimes. This study combines structural, geochemical and geophysical data to describe the evolution of Macquarie Island and the adjacent Australian-Pacific plate boundary from spreading to transpression.

The Finch-Langdon fault is the most significant spreading-related structure on the island, juxtaposing upper crust and intrusive/mantle rocks. On the basis of structural and petrologic data, I propose that this fault zone formed near the inside corner of a ridge-transform intersection (RTI) and that structures on the island are conformable with those in the surrounding seafloor.

Geochemical data for Macquarie Island basalts and peridotites suggest a complex evolution during the last stages of seafloor spreading. The volcanic section consists of enriched basalts formed by low degrees of partial melting. Basalt geochemistry combined with stratigraphic relationships reveal early intervals of variable enrichment followed by periods of more constant, decreasing enrichment.

Peridotite and basalt geochemistries differ distinctly. Peridotites show characteristics of a high degree of melting (heavy rare earth element, or REE, and Al depletion), whereas low degrees of partial melting are inferred for the basalts. The mantle rocks also have spoon-shaped REE patterns and anomalous Sr enrichment. The depletion and trace element patterns are more typical of mantle rocks in ophiolites than of abyssal mantle.

Ridge propagation proximal to an RTI exposing lower crust/uppermost mantle would satisfy these structural and geochemical parameters.

Subsequently, transpression along the Australian-Pacific plate boundary has resulted in transform motion along the plate boundary and vertical deformation along the ~1500 km long Macquarie Ridge Complex. Uplift faults on the island are dominantly high-angle, en echelon, normal faults. The geometries and kinematics of the faults do not match predicted fault patterns for transpression, but indicate domination by extensional relay zones between step-overs of faults along the plate boundary.

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A CALCIUM ISOTOPE GROWTH SERIES OF THE DOMESTIC CHICKEN (GALLUS GALLUS)

Patrick Vaughan Wheatley, M.S. Geo. Sci.

The University of Texas at Austin, 2004

Supervisors: Christopher Bell and Libby Stern

The traditional roles of stable isotopes in paleontology are as indicators of diet or climate. An emerging field of paleontology and geochemistry is to use isotopes in order to make inferences about extinct and fossil animal physiology and behavior. Using bones from animals that minimally remodel their hard tissues, it may be possible to use isotopes to infer processes that occurred during early skeletal development. To examine potential isotope signatures of early development, I constructed a calcium isotope growth series for extant domestic chicken (Gallus gallus) embryos. I obtained Fertilized domestic chicken eggs and determined Ca isotope composition of the albumen, yolk, eggshell, and embryonic bone. The eggs ranged in ontogenetic age from 10-20 days after oviposition.

Yolk and shell components have d 44Ca values roughly consistent with those generated by other researchers on unfertilized eggs. The d 44Ca values of all egg components showed significant heterogeneity among individuals. Prior studies of the Ca isotope composition of adult vertebrates (including fish, mammals, and some reptiles) showed that the d 44Ca values of food and soft tissue were approximately equal, but mineralized bone lower by about 1.3‰. In contrast, the embryonic bone measured in my study was characterized by a d 44Ca value that was higher than the primary source of Ca (shell) by about 0.4‰ and about the same as the secondary source of Ca (yolk). This result indicates yolk is a much more important source of calcium for the developing bone than was previously thought, or the egg environment is causing a fractionation of calcium isotopes opposite of that which has been seen in prior studies. This unique isotope composition of embryonic bone may, pending further study, provide a chemical marker of oviparity. Additional research is needed in order to reach a definitive conclusion about why calcium isotopes are behaving differently in eggs of Gallus than in previous studies.


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HILLSLOPE SEEPAGE EROSION, SPRING SAPPING, AND KNICKPOINT MIGRATION: EVIDENCE OF GROUNDWATER SAPPING MIDDLE TRINITY AQUIFER, HONEY CREEK BASIN, COMAL COUNTY, TEXAS

Kristin Miller White, M.S. Geo. Sci.

The University of Texas at Austin, 2004

Supervisor: John M. Sharp, Jr.,

Geomorphic features within Honey Creek basin are consistent with formation by spring sapping which is the erosion of soil and rock by groundwater. Geomorphic evidence includes: swallow holes (stream swallets) that pirate spring discharge into the subsurface, groundwater piping and seepage along weathered marly slopes, headward erosion at knickpoints and spring orifices, fracture controls on incised streams, and generation of alluvium from scarp collapse. Erosion pins were used to measure erosion and sediment accumulation on marly slopes. Aerial photograph interpretation, Arcview GIS, 3D Analyst, and Geoorient techniques were used to evaluate the physical hydrogeologic features (potentiometric surface, karst springs, recharge features, knickpoints, and fractures) and their relationship to surface erosion patterns. Honey Creek basin is underlain by interbedded marl and limestone units of the Cretaceous Middle Trinity aquifer. Springs and caves provide a window into subsurface processes, including flow direction along preferential flowpaths and perched water tables. Precipitation affects spring discharge and water table levels in both stratigraphically perched aquifers and deeper aquifers. Upland karst features allow recharge of surface water to focus flow into spring conduits that rapidly discharge into streams following intense precipitation. Spring conduits and upland creeks feed into intermittent tributaries, then into perennial channels of Honey Creek and the Guadalupe River. Perched aquifers focus flow toward intermittent springs, while perennial springs are supported by a deeper regional system. Transmissivity is high within rock units that contain solutionally enlarged fractures and spring conduits. Elsewhere, the transmissivity of limestone and marl is generally low so that preferred flow pathways concentrate spring discharge where hillslope erosion has intersected bedding planes, conduits, and fractures. As springs discharge into local surface water bodies, erosion occurs at the spring orifices causing headward erosion along the pathways. Dominant fracture trends within the basin are generally aligned with the northeast-trending Balcones Fault Zone and a secondary fracture distribution to the northwest. These trends strongly influence spring location and sapping.

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A REVISION OF HELICOPLACOIDS AND OTHER EARLY CAMBRIAN ECHINODERMS OF NORTH AMERICA

Bryan Charles Wilbur, Ph.D.

University of Texas at Austin, 2005

Supervisor: James Sprinkle

The Lower Cambrian rocks of North America contain the remains of several species of echinoderms, including helicoplacoids, the eocrinoids Gogia, Lepidocystis, and Kinzercystis, and the edrioasteroids Camptostroma and Stromatocystites.

Camptostroma roddyi Ruedemann, 1933 is a large echinoderm from the Lower Cambrian Kinzers Formation of southeastern Pennsylvania. The animal has a unique dual-layered oral surface, and a large aboral suction pad used for attachment to skeletal debris. Thought by some authors to be ancestral to the edrioasteroids, it clearly belongs in a clade with the other early edrioasteroids.

Helicoplacoids are from the Lower Cambrian Poleta Formation and equivalent units across the western edge of North America. The group was thought to be represented by nine species; this number is reduced here to three species, with the remainder of helicoplacoid disparity accounted for by ontogenetic variation. These triradiate spindle-shaped echinoderms were capable of expansion and contraction by means of cloacal pumping, and attached to skeletal debris or semi-lithified matgrounds by means of a suction pad. Rather than representing an ancestral triradiate form that served as the template for a “2-1-2” ambulacral arrangement, these disparate echinoderms are derived from the ancestral pentameral edrioasteroid bauplan.

Gogia is well represented in the Lower Cambrian rocks of California and Nevada by five species, four of which are new and are described here. This is now understood to be the most diverse echinoderm genus from the Early Cambrian. Members of this group attached to skeletal debris by using a suction pad, and fed by employing retractable spiraled brachioles.

Stromatocystites walcotti Schuchert, 1919 is from Lower Cambrian rocks from Bonne Bay, Newfoundland. It is a flat edrioasteroid with a retractable suctorial aboral surface devoid of a pad. This morphologic feature delineates the group from other Middle Cambrian Stromatocystites, warranting renaming herein.

A tree generated for these groups shows that helicoplacoids, Gogia, Imbricata, and the eocrinoids (Gogia + Imbricata) all constitute monophyletic groups, while edrioasteroids are polyphyletic. Early Cambrian echinoderms are found with only one or (rarely) two species occupying the same morphospace, a pattern repeated by Middle Cambrian groups.

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THE SECONDARY PERMEABILITY OF “IMPERVIOUS” COVER IN AUSTIN, TEXAS

Thomas Jefferson Wiles, M.S. Geo. Sci.

The University of Texas at Austin , 2007

Supervisor: John M. Sharp Jr.

The term "impervious" is commonly used in urban settings to describe the permeability of buildings, roads, and parking lots. When estimating recharge to an aquifer underlying an urbanized area, impervious cover becomes a prime consideration. It is commonly assumed that an increase in impervious cover leads to a decrease in precipitation recharge. However, even a cursory glance at most roads, sidewalks, or parking lots reveals that, far from being impervious, there are abundant fractures that may provide avenues of infiltration. For this study, method was developed to determine the secondary permeability of pavements using a double ring infiltrometer to measure the infiltration rate of water into fractured pavements. Linear extrapolation is employed to determine the infiltration rate as the water depth approaches zero, which is used as a proxy for hydraulic conductivity by assuming that the gradient is unity.

Data were collected on concrete and asphalt pavements located in Austin , Texas , at each point a fracture or expansion joint intersected along 30-meter scanlines. By dividing the sum of the discharges for each fracture by the area represented by the scanline we are able to determine the equivalent-porous-media hydraulic conductivity. The equivalent hydraulic conductivities for discrete fractures were found to range at least three orders of magnitude, from >10 -2 to 10 -5 cm/sec; scanline hydraulic conductivities range two orders of magnitude from >10 -4 to 10 -6 cm/sec; permeability along the scanlines tends to be dominated by one or two highly conductive fractures; and the hydraulic conductivity of the entire paved surface is 5.9·10 -5 cm/s. Both apertures and point hydraulic conductivities were found to have logarithmic distributions but cross plots demonstrated no correlation, which indicated that a combination of the fill material and sub grade, not the fractures and expansion joints themselves, limit infiltration. By multiplying the paved surface hydraulic conductivity by the time the surface can be expected to be saturated, we find that 170 mm or 21 percent of mean annual rainfall is available as potential recharge. When coupled with an enhanced subsurface permeability structure resulting from the installation of utilities and the reduction of evapotranspiration from the reduction of vegetation, the net effect of roads and parking lots could be an increase in precipitation recharge.

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POLYCYCLIC AROMATIC HYDROCARBONS IN THE BOTTOM SEDIMENTS OF TWO URBAN LAKES, DENVER, COLORADO

Jennifer Thensom Wilson, M.S. Geo. Sci.

The University of Texas at Austin, 2001

Supervisors: Philip Bennett, Peter Van Metre

Gravity cores of bottom sediments were collected from two lakes in the Denver, CO, area in August 1997 and analyzed for polycyclic aromatic hydrocarbons (PAHs), cesium-137 for dating purposes, organic carbon, and other organic and inorganic constituents by the U.S. Geological Survey as part of the National Water-Quality Assessment (NAWQA) Program Reconstructed Trends study. Sediment cores from Sloan Lake, a naturally formed lake west of downtown Denver, chronicle nearly 130 years of sediment accumulation and record the effects of urbanization on the lake's drainage area. PAH concentrations in Sloan Lake's bottom sediments increase dramatically during the 1960s, and concentrations approach the probable effects level (PEL) of recommended sediment quality guidelines for total PAHs and exceed the guidelines for several individual PAH compounds. The bottom sediments in Cherry Creek Reservoir, constructed in 1953 in the southeastern suburbs of Denver, have very low PAH concentrations, although concentrations increase in the most recently deposited sediments. Source identification ratios show that the PAHs at both coring locations are derived mainly from combustion sources. Comparisons of the PAH assemblages in the sediments to combustion source indicator ratios derived from numerous studies of emissions indicate the majority of PAHs in Sloan Lake are derived from a combination of automotive and wood burning emissions while the PAHs in the sediments of Cherry Creek Reservoir are overwhelmingly from automobile emissions with only a slight influence from wood burning emissions.

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RESERVOIR CHARACTERIZATION OF THE CRUSE FORMATION, SOUTHERN TRINIDAD

René Ravi Winter, M.S. Geo. Sci.

The University of Texas at Austin , 2006

Supervisor: Ronald J Steel

Outcrop study, integrated with core, well, and seismic data has allowed a study of the Cruse Formation of Southern Trinidad in a depositional systems and sequence stratigraphic framework. The Formation represents a 3 rd order, Regressive – Transgressive depositional sequence, shallowing from a deep-water, slope dominated setting to a storm-wave influenced outer shelf with deltas, that is overlain by a transgressive shelf that supported retreating fluvially and tidally influenced shorelines. The Formation is capped by a major regional flooding interval, the Lower Forest Clay. Reservoir intervals within the Cruse represent a number of sub-environments that are differentiated by systems tract, ranging from prograding shelf-edge distributary mouth bars, thin-bedded turbidites and basin-floor fans of the Falling Stage and Lowstand Systems Tract (FSST and LST) to storm-influenced delta front and distributary channel fill, bayhead deltas, tidal flats and crevasse splays of the Transgressive and Highstand Systems Tract (TST and HST). Regressive – transgressive units like this repeat and stack 6-7 times in the overall Cruse development.

From a depositional systems perspective, reservoirs in the Cruse are superficially similar to reservoirs in the more prolific offshore settings. However, the Cruse Formation records a more fluvially influenced, strongly progradational evolution across an open, unstructured shelf platform whereas offshore Columbus Basin reservoirs exhibit a much more wave influenced, aggradational architecture, in a growth-fault dominated shelf setting. This results in significant differences in reservoir properties. Cruse reservoirs are much thinner and laterally more extensive than stacked, thicker but laterally confined (to growth compartments) offshore equivalents, resulting in a much higher hydrocarbon yield per unit area in the latter. The growth structures of the latter also provide more abundant traps.

The work has allowed for a better understanding of reservoirs in the Cruse Formation, which serves as an important tool for present, as well as future exploratory and production activity planned for onshore Trinidad .

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TEXAS GROUNDWATER MANAGEMENT: EQUITABLE APPORTIONMENT AND THE ADOPTION OF THE RESTATEMENT (SECOND) OF TORTS REASONABLE USE DOCTRINE

Travis William Witherspoon, M.A.

The University of Texas at Austin, 2008

Supervisor: Charles G. Groat

57 pages, 16 references

The rule of capture has governed Texas groundwater for over 100 years. Increased competition and aquifer drawdown created the necessity for the application of additional regulatory framework: groundwater conservation districts (GCDs) were created to serve this purpose. GCDs are local governmental bodies and by majority reside within single county boundaries. GCDs issue production permits, monitor aquifer levels, and predominantly regulate withdrawals through well spacing. GCDs are increasingly applying the doctrine of prior appropriation to their districts in order to allocate groundwater. Water rights allocation through prior appropriation has historically been applied to surface water, yet, when applied to groundwater, management complexities and water rights inequities readily emerge. Prior appropriation advantages users who have historically produced as well as those with immediate demands and financial means to meet those needs. Absent substantial tract ownership provisions as they correlate to just apportionment of groundwater, landowners who do not produce, or are not included in large-scale contractual production agreements, may experience a curtailing---or altogether extinguishing---of their water rights and the realization of the value of the resource beneath their property.

It is unclear whether GCDs institute prior appropriation permitting due to observance of precedence or familiarity with its surface water application; it is clear that GCDs have the discretion and authority to adopt alternative management doctrines. The Restatement (second) of Torts Reasonable Use doctrine stands out as the most progressive and equitable among the potential alternatives. It allows for the application of a set of test factors to weigh withdrawals and uses tract ownership as a measure of apportionment rather than purely priority. The Restatement treats all uses equally---past, present, or future---and subjects all uses to the burden of depletion. The Restatement could be adopted immediately by GCDs across the state. If adopted at the state level it would protect areas without GCD protection and address potential conflicts among GCDs. The guidelines of the Restatement have the potential to broaden a GCD’s discretion when evaluating withdrawals and protect the rights of all landowners equally.

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HYDROGEOLOGY OF THE CUATROCIÉNEGAS BASIN, COAHUILA, MEXICO: AN INTEGRATIVE APPROACH TO ARID KARST AQUIFER DELINEATION

Brad David Wolaver, Ph.D.

The University of Texas at Austin, 2008

Supervisor: John M. Sharp, Jr.

316 pages, 203 references, 40 tables

The Cuatrociénegas Basin is located in the Chihuahuan Desert, Coahuila, Mexico. Over 500 springs and groundwater-dependent ecosystems with >70 endemic species flank the 2,600-meter Sierra San Marcos that bisects the 1,200 square kilometer valley. The west sub-basin contains fracture-controlled springs with elevated relative discharge (~85 percent of total), temperature (~31.0°–34.0°C), and total dissolved solids (~90 milligrams/liter chloride) compared to the east sub-basin, that has stratigraphically-controlled springs with lower relative discharge (~15 percent), temperature (~28.0°–30.0°C), and total dissolved solids (~30 milligrams/liter chloride). Canals convey spring discharge out of the formerly closed valley. Groundwater development since the 1980s lowered groundwater levels >10 meters in adjacent basins and caused some springs to cease flowing.

The author hypothesizes that (1) both local and regional recharge are significant, (2) an integrative data approach can delineate recharge zones, and (3) the low-elevation of the Cuatrociénegas Basin, fault-associated secondary carbonate aquifer permeability, and stratigraphic influences on permeability control spring locations. To test these hypotheses, the research (1) develops hydrogeologic conceptual models of recharge areas using remotely-sensed topography, hydrogeologic data (e.g., spring geochemistry, temperature, and discharge), and geologic mapping; (2) delineates recharge areas by sequentially including upgradient catchments to match observed spring discharge using geographic information system catchment delineation, chloride-balance recharge estimation, and analytical model interbasin flow evaluation; (3) explains spatial variations in spring chloride, discharge, and temperature using environmental tracers (e.g., δ18O, noble gases, 3H) and an elevation-dependent recharge rate; and (4) uses land gravimetry surveys to generate best-fit hydrogeologic cross sections in areas of high spring density.

The author concludes that local precipitation is insufficient to generate observed spring discharge. Waters with <0.1 tritium units indicate regional flow and aquifer residence times of >50 years. Water-budget based catchment delineation suggests west basin fractures tap a (>10,000-square kilometer) regional carbonate aquifer. Thus, groundwater management should be extended outside the Cuatrociénegas Basin. East basin canyons intersect the potentiometric surface of a stratigraphically controlled (local/regional) aquifer recharged in the 500-square kilometer Sierra San Marcos. Sierra La Madera recharge explains Ocampo Valley predevelopment flow and chloride concentration. This approach can be applied to delineate similar developing arid aquifers.

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UPPER MIOCENE DEPOSITIONAL HISTORY OF THE CENTRAL GULF OF MEXICO BASIN

Xinxia Wu, Ph. D.

The University of Texas at Austin, 2004

Supervisor: William E. Galloway

319 pages, 119 references

The Upper Miocene (late Middle to early late Miocene) depositional episode, defined by two widespread, transgressive deposits associated with biostratigraphic tops Textularia W (12.0 Ma) and Robulus E (6.2 Ma), records a long-lived family of sediment dispersal systems that persisted for nearly 6 m.y. with little modification. It corresponds to a prolonged lowstand after a dramatic sea-level fall at the end of the middle Miocene and is punctuated by three additional flooding events associated with Cibcides carstensi , Discorbis 12 and Cristellaria K biostratigraphic tops, which subdivide the Upper Miocene depositional episode into four secondary depositional episodes.

In the east-central Gulf of Mexico, the Upper Miocene genetic sequence records extensive continental margin offlap, primarily centered on the ancestral Tennessee River and Mississippi River dispersal axes. Thickest sediments were deposited in the Tennessee River delta beneath modern southeast Louisiana. The composite fluvial-dominated, wave-modified Tennessee and Mississippi delta system rapidly built beyond the subjacent Middle Miocene shelf margin to construct a sandy delta-fed apron that ultimately spilled distal sandy turbidites onto the adjacent basin floor. Margin outbuilding was locally and briefly interrupted by hyper-subsidence due to salt withdrawal and consequent slope mass wasting, forming numerous depocenters separated by salt massifs and ridges, and various linked structural systems. A broad, but relatively thin, sandy strandplain and clastic shelf succession, supplied by reworking of the deltaic deposits, extends both eastward and westward from the delta system. Abundant strike-reworked sediment locally prograded the strandplain to the shelf edge, with slope offlap exceeding 30 mi (50 km).

A large volume of sand continuously bypassed the confined minibasin and upper slope at the flank of active deltaic depocenters into the Mississippi Canyon, Atwater Valley and Green Canyon OCS areas throughout the entire Upper Miocene, forming a linked, long-lived McAVLU intraslope and abyssal fan system in the primary minibasin corridor of the lower slope and basin floor. Sand bypass and subsequent deposition was dominantly through the slope canyon and intraslope fan systems developed in the east-central Gulf. Canyons, fan valleys, leveed channels, gravity mass transport complexes and structural conduits that focused sediment flow provide various sediment transport elements.

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A 3-D SEISMIC INVESTIGATION OF THE DISTRIBUTION OF GAS HYDRATE AND FREE GAS AND THEIR RELATIONSHIP TO THE STRUCTURE AND STRATIGRAPHY OF HYDRATE RIDGE

Hao Xun, M.Sc.

The University of Texas at Austin , 2007

Supervisors : Nathan L. B. Bangs and Paul L. Stoffa

A bottom simulating reflection (BSR) that parallels the sea floor occurs on the seismic profiles from Hydrate Ridge, Oregon continental margin. In 2000 a 4x10 km 2 3-D high-resolution seismic survey was conducted on south Hydrate Ridge on the Oregon continental margin . The objective of the survey is to characterize the regional pattern of fluid and gas migration and its relationship to hydrate accumulations on Hydrate Ridge. These data were acquired with a high-resolution seismic source with source-receiver offsets of up to 644 m, which results in incidence angles of up to 20 degrees at BSR. In 2002 new 2D seismic data with source-receiver offsets of up to 1500 m, producing incidence angles of up to 40 degrees at BSR, were collected in Ewing Cruise EW0208 in coordination with Ocean Drilling Program (ODP) Leg 204. My goal in this thesis is to use 3-D high-resolution seismic data offshore Oregon to evaluate the distribution of free gas and gas hydrate by amplitude-versus-offset (AVO) analysis, and to relate the distribution of free gas and gas hydrate to the structure and stratigraphy of Hydrate Ridge.

Prior to AVO analysis, I conducted the true amplitude recovery by using the seismic range equation, and the true amplitude processing through prestack time migration. Although the 3-D high-resolution seismic data is of good S / N ratios, I found by observation and computation that the amplitude in the 3-D data is anomalous or incorrect. So I also calibrated the 3D data by using the new 2D data to remove unfavorable acquisition effects in the 3D survey.

On prestack-migrated gathers, I picked up the seismic amplitude from the three surfaces associated with free gas accumulations: 1) the bottom simulating reflection (BSR), 2) Horizon A, and 3) Horizon B'. Intercept and slope are obtained from AVO fitting, and the Poisson's ratio obtained by using intercept and slope with the constraints of well-log data. Free gas saturation for the three surfaces is estimated by fluid substitution technique. The estimated gas saturation from seismic data is compared with that from the resistivity and t he pressure core sampler (PCS)

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SEQUENCE STRATIGRAPHY AND DEPOSITIONAL SYSTEMS OF LATE CENOZOIC SEDIMENTS, MATAGORDA BAY, GULF OF MEXICO

Songul Yildiz, M.S. GeoSci

The University of Texas at Austin, 2003

Supervisor: William L. Fisher and Robert G. Loucks

157 pages, 60 references, color figures

This study focuses on the Late Cenozoic sediments of Matagorda Bay, Gulf of Mexico. The database consists of 100 mi2 coverage, 1.8 seconds penetrated 3-D seismic and well-log data from 41 wells.

Structural and stratigraphic cross-sections, a composite log, isopach maps, horizon amplitude maps, stratal slices, and a fence diagram have been prepared to define the structural framework, sequence stratigraphy, and depositional systems of Matagorda Bay. Basic sequence stratigraphic concepts from the Exxon model have been applied to define the sequence stratigraphic framework.

The lower Miocene to Pleistocene interval of the Upper Cenozoic clastic sediments in Matagorda Bay is identified as a lowstand system tract (LST), trangressive system tract (TST), and highstand system tract (HST). Main deposition occurred during the Early Miocene stage. This stage is represented by four third-order sequences (SEQ1, SEQ2, SEQ3, and SEQ4). SEQ3 is the approximately 700 ft of amalgamated sand bodies. The middle Miocene is represented by one third-order sequence (SEQ5) that reaches up to 500 ft in thickness. The Upper Miocene is represented by one third-order sequence (SEQ6_1), which is the thinnest sequence of the studied section. There are some barrier-island depositional features identified on the stratal slice amplitude maps for this period. The Pliocene is represented by three third-order sequences (SEQ6_2, SEQ7, and SEQ8). The thickness of Pliocene sediments is approximately 700 ft. The Pleistocene interval is represented by one third-order sequence (SEQ9), which is characterized by transgressive and highstand stratigraphic units.

Sixteen individual lowstand sand units have been identified in the studied section. The correlation of the sand units is displayed on figures. However, net-sand isopach maps for each sequence were more representative for identifying depositional features. Therefore, 11 isopach/net-sand maps were created for lowstand sandy units of SB1_1, SEQ1, SEQ2, SB3_1, SB3_2, SB4_1, SEQ4, SEQ5, SEQ6_2, SEQ7, and SEQ8. Examination of the isopach maps shows that the Matagorda Bay subbasin was fed from the northwest and west, and rarely from the north. Predominant incisions started first in southwest, later in the middle, and finally in the northeast parts of the study area. Incised valley axes are mainly oriented northwest-to-southeast.

Structures identified in the study area are mainly northeast-to-southwest oriented growth faults and some antithetic faults, which produced a small basin in Matagorda Bay. Most sedimentation occurs in this small basin and is controlled by these syndepositional fault systems. These fault zones are divided into three major geographic groups: (1) North Fault Zone, (2) Middle Fault Zone, and (3) South Fault Zone. Structural orientation shows that its major syndepositional structures were the most active during Early Miocene time.

The products of this study do not represent the dominant depositional system because of insufficient data in Lower Miocene strata. The characteristic features of the depositional system were superimposed. On the other hand, regional studies that have more dense data than this study interpreted that Matagorda Bay and its surrounding areas were located in the shore-zone in Early Miocene time. The same result was also verified in this study and discussed in related section.

The studied section of Upper Cenozoic strata in Matagorda Bay from the Early Miocene to Recent indicates that strata in Matagorda Bay show an aggradational and retrogradational pattern that can be followed from logs, seismic amplitude maps, and stratal slices. Fluvial - deltaic dominated systems can be identified from stratal slice and amplitude maps. Examination of stratal slices from bottom to top shows the fluvial-deltaic system with different cycles, but interestingly, the main sandy units (in LST) are deposited as incised valley fills. Distribution of sand bodies, combination of stratal slices, horizon amplitude maps, and isopach maps, suggest that the Matagorda Bay subbasin was fed mainly from the northwest and west, and rarely from the north. As a result, complex fluvial and deltaic systems mixed together in the Matagorda Bay subbasin during Late Cenozoic time. The same sediment pathways were still active during Pleistocene time and were filled by Recent lagoonal sediments in Matagorda Bay.


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EFFECTIVE POROSITY ESTIMATION FROM 3D SEISMIC REFLECTION DATA: MARCO POLO FIELD, GULF OF MEXICO

Gregory Russell Young, M.S. Geo. Sci.

The University of Texas at Austin, 2007

Supervisor : Mrinal K. Sen

163 pages, 123 references

Seismic inversion is a geophysical tool that uses geologically constrained physical models to infer elastic interval properties (e.g., P-velocity, S-velocity, and density) from seismic interface data (e.g., reflection amplitude and moveout). This thesis focuses on one such application to pre-stack seismic data from the Marco Polo Field, deepwater Gulf of Mexico. I compare the usefulness of post-, partial-, and pre-stack seismic inversion methods for estimating effective porosity by 1) inverting the Marco Polo Field seismic data with post-, partial-, and pre-stack seismic inversion methods, 2) transforming the estimated elastic parameters into effective porosity via fluid-dependent transformations derived from borehole data, and 3) interpreting all results in terms of inverse theory, rock physics, and the Marco Polo Field geology.

I derive fluid-dependent transformations that are calibrated to the Marco Polo Field by cross-plotting measured elastic parameters (i.e., well logs) against petrophysical logs for gas-, oil-, and brine-saturated intervals in the wells. Cross-plot analysis indicates that density is best-suited for estimating effective porosity because the steep gradient of the density-to-effective porosity transformation implies minimal error magnification during mapping from the elastic parameter domain to the reservoir characteristic domain. The shallow gradient of the P-impedance-to-effective porosity transformation gradient results in substantial error magnification. Although density is the choice parameter for estimating effective porosity, deterministic linear seismic inversion methods have historically failed to resolve density. Post-stack inversion methods, which parameterize the model space with the single parameter P-impedance, provide no information about density. Partial-stack inversion methods fail to resolve density from angle-dependent amplitude variations because the NMO corrected gathers, upon which partial-stack inversions rely, have a separate null space that contains the necessary information to separate density from velocity within the impedance estimates. Pre-stack seismic inversion methods utilize the full waveform data (i.e., amplitude and moveout) and show great potential for estimating mass density. However, pre-stack seismic inversions are viewed as impractical due to high computation costs, and they are typically only applied to a few CMP’s or over small time windows.

Using the Miocene submarine fan system in the Marco Polo Field as a case study, I invert the 3D pre-stack seismic volume with a computationally efficient pre-stack seismic inversion algorithm, and I demonstrate that only full-waveform nonlinear pre-stack inversion accurately resolves density and estimates effective porosity within the deepwater system. The density and effective porosity estimates accurately tie with a type well with VSP, and they both correctly model the a priori structural and stratigraphic information in the Marco Polo Field. Moreover, the pre-stack inversion algorithm is able to resolve all model parameters from nearly flat initial models.

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FALSE POSITIVE SEISMIC “BRIGHT SPOTS” AND DISCRIMINATION BETWEEN GAS AND BRINE SATURATION USING MULTIPLE AVO ANALYSIS TECHNIQUES IN THE COLUMBUS BASIN, OFFSHORE TRINIDAD

Kathryn Teresa Young, MSGeoSci

The University of Texas at Austin, 2006

Supervisor : Robert H. Tatham

Exploratory drilling in the Tertiary Columbus Basin , offshore Trinidad has targeted high amplitude anomalies or “bright spots” in stacked sections with the expectation that these high amplitude reflectors will be gas-saturated sands. Many of these “bright' reflection events are brine-saturated sands or tight, uncommercial gas-saturated silts. Thus, they are often characterized as “False Bright Spots”.

This study investigates the use of Amplitude Variation with Offset (AVO) techniques to discriminate bona fide gas-saturated “bright spots” from false brine-saturated “bright spots”. Three AVO analysis techniques utilizing well log data and 3-D seismic data were applied to 4 different study areas within the Columbus Basin: Intercept (A) and Gradient (B), Elastic Impedance (EI) inversion and Lambda-Mu-Rho (LMR) inversion. A total of 20 prospective intervals were evaluated.

The three AVO analysis techniques were all successful in determining the type of fluid saturation in the vast majority of the case studies. In most cases simple A-B crossplotting was sufficient to discriminate gas-saturation from brine-saturation and in two exceptions where it was not effective, the other methods, EI and LMR inversion, were successful in all but 1 of the 20 intervals examined. Application of all three techniques is recommended as a means of cross-validating results and increasing the reliability of results and interpretation. In addition, the more complex inversion methods demonstrated potential to be lithology indicators between sandy and shaly lithologies.

The Rock Physics and AVO analyses presented in this study provide a reliable method to discriminate gas-saturated and brine-saturated sediments, including “False Bright Spots”, and contributes to the overall geophysical understanding and characterization of the Columbus Basin; an area where research and investigations of this nature are rare. Further, this is also a new case study of LMR inversion involving younger Tertiary sediments. As part of this study, a new “mudrock” line with coefficients relative to the Columbus Basin has been developed for estimation of seismic shear wave velocities from conventional sonic log data.

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THE AMPLITUDE PRESERVATION CHARACTERISTICS OF CONVENTIONAL PROCESSING AND IMAGING OF SEISMIC DATA

Patricia Yu, MSGeoSci

The University of Texas at Austin , 2007

 

Supervisors: Robert J. Ferguson, Robert Tatham

The usual analysis of variations in reflection amplitude versus angle of incidence (AVA) and subsequent inversion is often implemented to estimate the rock and fluid properties. The objective of this study is to demonstrate the capability of forward modeling and the effect of subsequent processing and migration on conventional amplitude analysis. Potential pitfalls in imaging assumptions limiting effective AVO analysis are examined. This study will contribute to future work in which conventional analysis in the amplitude-angle domain is compare with that of analysis in the amplitude-ray parameter domain.

For this purpose, I perform forward modeling on a simple set of synthetic data and a more complex geologic model based on the Teal South field using a finite difference acoustic modeling algorithm and a visco-elastic ray-tracing modeling method followed with subsequent time and depth migrations applied. The study shows that even minimal processing of this simple model has the potential to drastically impact reflection amplitude. From the simplistic case study, the acoustic modeled data appears to have valid amplitudes at mid angle ranges that can be determined for migrated AVA to correlate to the Zoeppritz model. However, these ranges of validity do not appear to apply to all migration modules when the model is more complex, perhaps to due to aliasing of offsets in the CMP. Finite difference modeling does produce better synthetics in areas of more complex geological structure.

A more advanced processing algorithm does not necessarily mean the output will have a more accurate representation of the model. While the depth migrated images do show better spatial positioning of events and reduce amplitude distortion, as expected, when compared to the time migrated images, it also suffers from artificial AVA effects likely due to irregular trace distribution. Kirchhoff migrations are especially susceptible to insufficient fold and spatial sampling. For this study, more primitive migration algorithms perform better in regards to amplitude preservation than their more complex counterparts. The conclusion is that AVA preservation and imaging algorithms would benefit from integrated development of imaging and amplitude preservation algorithms.

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A NEW THEORETICAL MODEL FOR GROWTH OF THE ECHINOID TEST

Louis George Zachos, Ph.D.

The University of Texas at Austin, 2008

Supervisor: James Sprinkle

A new developmental model for growth of the echinoid test is based on a review of the growth patterns in regular echinoids. Echinoids are structurally composed of a tessellation of hundreds to thousands of individual plates. The two major aspects of echinoid growth are treated separately. (1) New plates are added in accordance with the Ocular Plate Rule and plate addition is hypothesized to be constitutively active but inhibited by a morphogen originating in coronal plates. Morphogen production is modeled as an inverse function of plate size and the concentration of inhibiting morphogen at a plate nucleation point is inversely proportional to the distance from surrounding plate centers. Plate addition is triggered whenever the inhibiting morphogen concentration falls below a threshold value. (2) The growth of individual plates is described using the Bertalanffy growth equation to model change in plate perimeter.

The geometric model is based on a spherical frame of reference, and all calculations of position and growth are modeled over the surface of the sphere (i.e., along geodesics). The data structure defined to maintain the geometric parameters is based on a spherical Delaunay triangulation of plate centers, and the edge geometry approximated by the dual Voronoi polygonalization. Echinoid plates are thus modeled as Voronoi polygons covering the sphere. Growth is modeled by the increasing radius of the sphere and the changing topology of the plates as new plates are added and existing plates grow. Final form of the complete test is generated by an affine deformation of the sphere.

The growth model is implemented as the program EFORECHINOID, coded in the object-oriented programming language C++ with significant usage of the Standard Template Library (STL) for efficient coding and memory management. Most parameters are available to a user via a Graphical User Interface (GUI), and output of 3-dimensional simulations is via standard 3-D AutoCAD® Drawing Exchange Format (DXF) files. Program efficiency is O(nlogn) and reasonably parameterized growth simulations with several hundred time steps can be performed in a matter of minutes per run.

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INTEGRATED SEQUENCE STRATIGRAPHY, DEPOSITIONAL ENVIRONMENTS, DIAGENESIS, AND RESERVOIR CHARACTERIZATION OF THE COTTON VALLEY SANDSTONES (JURASSIC), EAST TEXAS BASIN, USA

Qianru Zeng, MSGeoSci

The University of Texas at Austin, 2004

Supervisor: Zong-Liang Yang

This study examines how snow cover depends on snow depth, latitude, vegetation type, and terrain using a wide variety of data sources. These datasets come from the Moderate Resolution Imaging Spectroradiometer (MODIS), Advanced Very High Resolution Radiometer (AVHRR), National Operational Hydrologic Remote Sensing Center (NOHRSC), and U.S. Air Force Environmental Technical Application Center (USAF/ETAC).

Monthly variations of MODIS snow cover fraction (SCF) and USAF/ETAC snow depth (SD) show that the magnitude and timing of the peak snow cover and snow depth depends on latitude, vegetation cover and terrain. The higher the latitude, the greater the SCF and SD, and the later the snowmelt processes initiate. The same is true for the mean elevation and the standard deviation of elevation.

The temporal variations of snow can be divided into two distinct periods, the accumulation period and the ablation period. In the accumulation period, which is usually from September to February, SCF increases as SD increases. In the ablation season, which is usually from March to August, the SCF decreases as SD decreases.

The effects of latitude bands, vegetation cover, mean elevation, and standard deviation of elevation provide a reasonable explanation for temporal variations of snow cover and snow depth over ten selected regions in the Northern Hemisphere. Of the four factors, latitude has the greatest effects. Variability within the same latitude regions can be attributed to topography differences and vegetation cover differences.

SCF is positively correlated to SD: when snow is shallow, SCF increases rapidly as SD increases, and when snow is deep, SCF changes little as SD continues to increase. This SCF-SD relationship is confirmed for different seasons, different vegetation covers, different mean elevations, and different standard deviations of elevation. The tanh-form of the SCF-SD relationship proposed by Yang et al. (1997) with different Z values is shown to work well for flat and non-forest areas. The sensitivity of the SCF-SD relationship to scaling is low over a range of spatial resolutions from 120 km down to 1 km, and over a range of temporal scales from monthly (MODIS and USAF) to daily (NOHRSC).


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