University of Texas at Austin
Libraries Home | Mobile | My Account | Renew Items | Sitemap | Help |
support us

University of Texas Libraries

University of Texas Libraries
Celebrating the Life

About

Find Articles

Theses
and Dissertations

Virtual Field Trip Guides

Geosciences
Links

Shell logo
orange divider

Geological Sciences Theses and Dissertations Abstracts: 2013 - Present

orange divider

The 2013 - Present abstracts are from Undergraduate Senior Honors Theses, Master's Theses, and PhD Dissertations completed at the University of Texas at Austin in the field of Geological Sciences. See the Geological Sciences Theses and Dissertations Index : 2013- Present for a more concise listing of authors, titles, and supervisors. Dissertation abstracts published prior to 2001 may be found through Dissertations and Theses: Full Text.


FRACTURE CHARACTERIZATION OF A CARBONATE RESERVOIR IN THE ARABIAN PENINSULA

Mohammed Abdullah Alhussain, Ph.D

University of Texas at Austin, May 2013

Supervisor: Mrinal K. Sen

138 pages, 76 references, 1 table

Estimation of reservoir fracture parameters, fracture orientation and density, from seismic data is often difficult because of one important question: Is observed anisotropy caused by the reservoir interval or by the effect of the lithologic unit or multiple units above the reservoir? Often hydrocarbon reservoirs represent a small portion of the seismic section, and reservoir anisotropic parameter inversion can be easily obscured by the presence of an anisotropic overburden. In this study, I show examples where we can clearly observe imprints of overburden anisotropic layers on the seismic response of the target zone. Then I present a simple method to remove the effect of anisotropic overburden to recover reservoir fracture parameters. It involves analyzing amplitude variation with offset and azimuth (AVOA) for the top of reservoir reflector and for a reflector below the reservoir. Seismic CMP gathers are transformed to delay-time vs. slowness (tau-p) domain. We then calculate the ratio of the amplitudes of reflections at the reservoir top and from the reflector beneath the reservoir. The ratios of these amplitudes are then used to isolate the effect of the reservoir interval and remove the transmission effect of the overburden.

The methodology is tested on two sets of models - one containing a fractured reservoir with isotropic overburden and the other containing a fractured reservoir with anisotropic overburden. Conventional analysis in the x-t domain indicates that the anisotropic overburden has completely obscured the anisotropic signature of the reservoir zone. When the new methodology is applied, the overburden effect is significantly reduced. The methodology is also applied to an actual PP surface reflection (Rpp) 3D dataset over a reservoir in the Arabian Peninsula. Ellipse-fitting technique was applied to invert for two Fracture parameters: (1) Fracture density and (2) fracture direction. Fracture density inversion results indicate increased fracturing in the anticline structure hinge zone. Fracture orientation inversion results agree with Formation MicroImaging (FMI) borehole logs showing a WNW-ESE trend.

This newly developed amplitude ratio method is suitable for quantitative estimation of fracture parameters including normal and tangential “weaknesses” (ΔN and ΔT respectively). Initially, inversion of conventional AVOA for ΔN and ΔT parameters indicates that the ΔN parameter is reliably estimated given an accurate background isotropic parameter estimation derived from borehole logging data. While ΔN parameter inversion is successful, inversion for ΔT parameter from Rpp information is not, presumably due to the dependence of ΔT estimation on many medium parameters for accurate prediction. The ΔN parameter is then successfully recovered when applied to the amplitude ratio values derived from synthetic data. It is important to recognize that ΔN parameter is directly proportional to fracture density and high ΔN values can be attributed to high crack density values.

The ΔN parameter inversion is also applied to the amplitude ratios derived from real seismic data. This inversion requires fracture azimuth data input that is obtained from the fracture direction inversion using ellipse-fitting technique. The background Vp/Vs ratio, estimated from well logs, is another required parameter for ΔN estimation. Inversion results are promising when fracture density computed from ΔN parameter is compared to the facture density computed from ellipse-fitting technique. The maps of both attributes show similarities with more fractures located at the anticline structure hinge. Spatial variability in fracture parameters has proven valuable in locating “sweet spots” areas or highly fractured zones within the reservoir interval.

Return to top | Return to Index


DEPTH-REGISTRATION OF 9-COMPONENT 3-DIMENSIONAL SEISMIC DATA IN STEPHENS COUNTY, OKLAHOMA

Mustafa Badieh Al-Waily, M.S. Geo. Sci.

University of Texas at Austin, May 2014

Supervisor: Bob Hardage

108 pages, 43 references, 10 tables

Multicomponent seismic imaging techniques improve geological interpretation by providing crucial information about subsurface characteristics. These techniques deliver different images of the same subsurface using multiple waveforms. Compressional (P) and shear (S) waves respond to lithology and fluid variations differently, providing independent measurements of rock and fluid properties.

Joint interpretation of multicomponent images requires P-wave and S-wave events to be aligned in depth. The process of identifying P and S events from the same reflector is called depth-registration. The purpose of this investigation is to illustrate procedures for depth-registering P and S seismic data when the most fundamental information needed for depth-registration – reliable velocity data – are not available.

This work will focus on the depth-registration of a 9-component 3-dimensional seismic dataset targeting the Sycamore formation in Stephens County, Oklahoma. The survey area – 16 square miles – is located in Sho-Vel-Tum oilfield. Processed P-P, SV-SV, and SH-SH wave data are available for post-stack analysis. However, the SV-data volume will not be interpreted because of its inferior data-quality compared to the SH-data volume. Velocity data are essential in most depth-registration techniques: they can be used to convert the seismic data from the time domain to the depth domain. However, velocity data are not available within the boundaries of the 9C/3D seismic survey.

The data are located in a complex area that is folded and faulted in the northwest part of the Ardmore basin, between the eastern Arbuckle Mountains and the western Wichita Mountains. Large hydrocarbon volumes are produced from stratigraphic traps, fault closures, anticlines, and combination traps. Sho-Vel-Tum was ranked 31st in terms of proved oil reserves among U.S. oil fields by a 2009 survey.

I will interpret different depth-registered horizons on the P-wave and S-wave seismic data volumes. Then, I will present several methods to verify the accuracy of event-registration. Seven depth-registered horizons are mapped through the P-P and SH-SH seismic data. These horizons show the structural complexity that imposes serious challenges on well drilling within the Sho-Vel-Tum oil field. Interval Vp/Vs – a seismic attribute often used as lithological indicator – was mapped to constrain horizon picking and to characterize lateral stratigraphic variations.

Return to top | Return to Index


SURFACE-RELATED MULTIPLE ELIMINATION AND VELOCITY-INDEPENDENT IMAGING OF A 2D SEISMIC LINE FROM THE VIKING GRABEN DATASET

Lubna Barghouty, Bachelor of Science

University of Texas at Austin, December 2013

Supervisor: Sergey Fomel

83 pages, 33 references, 2 tables

Free-surface multiples in marine seismic surveys constitute a significant type of noise in the data and a challenge in the seismic processing flow. Previous processing performed on a 2D line of the Viking Graben dataset from the North Sea showed the ineffectiveness of one demutiple method using moveout discrimination to attenuate surface-related multiples. Conventional seismic processing usually employs the labor-intensive step of velocity analysis in multiple attenuation methods exploiting moveout differences and in seismic imaging. In this project, I attempt to perform multiple attenuation and seismic imaging of the 2D data without the need for velocity analysis. We address the problem of surface multiples using the technique of Surface-Related Multiple Elimination (SRME), which generates a model of the multiples by autocon-volution of the seismic data and then adaptively subtracts the multiples. Multiple prediction and subtraction requires neither primary velocity estimation by velocity analysis nor wavelet estimation. The results of SRME proved satisfactory in adapting the predicted multiples to the actual multiples necessary for multiple elimination.

Since multiples were predicted from the data itself, preprocessing of the data such as missing trace interpolation was crucial for accurate multiple prediction. Imaging the data using a non-conventional method of Velocity-Independent Time-Domain Imaging was a suitable imaging step following SRME because it relies on dip estimation rather than velocity analysis to perform imaging tasks such as migration to zero offset and prestack time migration. A time-domain image was constructed of the 2D line showing diffraction patterns not collapsed by migration. Improvements on the migration results can be made by improving the dip estimation necessary for the imaging step, assuming the diffraction sources are not outside the 2D line.

Return to top | Return to Index


THE SEISMIC RESPONSE TO FRACTURE CLUSTERING: A FINITE ELEMENT WAVE PROPAGATION STUDY

Lauren Elizabeth Becker, M.S. Geo. Sci.

University of Texas at Austin, May 2014

Supervisor: Kyle T. Spikes

96 pages, 55 references

Characterizing natural and man-made fracture networks is fundamental to predicting the storage capacity and pathways for flow of both carbonate and shale reservoirs. The goal of this study is to determine the seismic response specifically to networks of fractures clustered closely together through the analysis of seismic wavefield scatter, directional phase velocities, and amplitude attenuation. To achieve this goal, finite element modeling techniques are implemented to allow for the meshing of discontinuous fracture interfaces and, therefore, provide the most accurate calculation of seismic events from these irregular surfaces.

The work presented here focuses on the center layer of an isotropic model that is populated with two main phases of fracture network alteration: a single large-scale cluster and multiple smaller-scale clusters. Phase 1 first confirms that the seismic response of a single idealized vertically fractured cluster is distinct crosscutting energy within a seismogram. Further investigation shows that, as fracture spacing within the cluster decreases, the depth at which crosscutting energy appears exponentially increases, placing it well below the true location of the cluster. This relationship holds until 28% of the fractures are moved from their uniformly spaced locations to random locations within the cluster. The vertical thickness of the cluster has little effect on the location or strength or the crosscutting signature.

Phase 2 shows that, although clusters of more randomly spaced fractures mask crosscutting energy, a marked decrease in amplitude coinciding with a bend in the wavefront produces a heterogeneous anisotropic seismic response. This amplitude decay and heterogeneous anisotropy is visible until cluster spacing drops below one half of the wavelength or the ratio of fractured material to matrix material within a cluster drops below 37%. Therefore, the location of an individual fracture cluster can be determined from the location of amplitude decay, heterogeneous anisotropy, and crosscutting energy. Furthermore, the density of the cluster can be determined from the degree of amplitude decay, the angle of heterogeneous anisotropy, and the depth of cross-cutting energy. These relationships, constrained by limits on their detectability, can aid fracture network interpretation of real seismic data.

Return to top | Return to Index


REGIONAL VARIABILITY IN MID-LATITUDE GLACIERS ON MARS FROM ORBITAL RADAR: IMPLICATIONS FOR FORMATION

Jesse Berney, Bachelor of Science

University of Texas at Austin, May 2013

Supervisor: Jack Holt

49 pages, 18 references

Debris-covered glaciers on Mars offer evidence that global climate change on Mars is governed by orbital forcings, in particular cyclical changes in obliquity. These glaciers or Lobate Debris Aprons (LDA) represent the movement of water from the poles to lower latitudes and can help constrain the quantities of water being transported during earlier parts of Mars's history. LDA also comprise a primary accessible quantity of water for future missions. By studying the characteristics of LDA in a regional sense, we can gain insight into modes of formation for these "Lobate Debris Aprons" and how they continue to exist in today's hostile climate. When examined with radar, LDA in the Deuteronilus Mensae and Tempe Mareotis regions of the northern hemisphere show a variation in reflective properties which correlates with geologic age of nearby escarpments, suggesting that the variation in radar properties may represent a difference in the properties of the debris cover rather than in the glaciers beneath.

Return to top | Return to Index


STRUCTURE OF THE PATAGONIAN FOLD-THRUST BELT IN THE MAGALLANES REGION OF CHILE, 53° - 55° S LAT.

Paul Michael Betka, Ph.D.

University of Texas at Austin, December 2013

Supervisors: Sharon Mosher and Keith Klepeis

224 pages, 146 references, 1 table

The southern Patagonian Andes record the Late Cretaceous closure and inversion of the Late Jurassic – Early Cretaceous Rocas Verdes marginal basin, subsequent development of the Patagonian retroarc fold-thrust belt and the Neogene to present tectonic superposition of a left-lateral strike-slip plate margin defined by the Magallanes-Fagnano fault zone. In this dissertation, I present new geologic maps, cross sections and detailed macro- and microscopic structural analyses that describe the geometry and kinematic evolution of the fold-thrust belt and superposed strike-slip deformation over ~200 km along-strike between 53° and 55° S latitude. Results are discussed in the context of the regional tectonic development of the southernmost Andes and are relevant to the understanding of important tectonic processes including the development of a retroarc fold-thrust belt, the formation of a basal décollement below and toward the hinterland of a fold-thrust belt and the spatial distribution of deformation along a strike-slip plate margin.

New maps and balanced cross-sections of the Patagonian fold-thrust belt show that it developed during two main phases of Late Cretaceous to Paleogene shortening that were partly controlled by the antecedent geology and mechanical stratigraphy of the Rocas Verdes basin. During the Late Cretaceous, a thin-skinned thrust belt developed above a décollement that formed first in relatively weak shale deposits of the Rocas Verdes basin and later deepened to ‹1 km below the basement-cover contact. Ramps that cut mechanically rigid volcanic rocks of the marginal basin link the two décollements. Basement-involved reverse faults that cut the early décollements and probably reactivate Jurassic normal faults reflect Paleogene shortening. Shortening estimates increase northwest to southeast from 26 to 37% over 100 km along-strike and are consistent with regional models of the fold-thrust belt.

Structural data, kinematic analyses, and microstructural observations from the lower décollement show that it is defined by transposition of several generations of northeast-vergent noncylindrical folds, shear bands, and a quartz stretching lineation that are kinematically compatible with first-generation structures of the fold-thrust belt. Quartz microstructural data from the décollement are consistent with deformation temperatures that decrease from ~500-650° C to ~400-550° C over ~75 km in the transport direction, indicating that the décollement dipped shallowly (~6°) toward the hinterland. The décollement decoupled the underthrust continental margin from the fold-thrust belt and exemplifies the kinematic relationship between shortening that occurs coevally in a retroarc fold thrust-belt and its polydeformed metamorphic 'basement'.

Fault kinematic data and crosscutting relationships show kinematic and temporal relationships between populations of thrust, strike-slip and normal faults that occur in the study area. Thrust faults form an internally compatible population that shows subhorizontal northeast-trending shortening of the fold-thrust belt and is kinematically distinct from populations of normal and strike-slip faults. Both strike-slip and normal faults crosscut the fold-thrust belt, are localized near segments of the Magallanes-Fagnano fault zone, have mutually compatible kinematic axes and are interpreted to be coeval. Strike-slip faults form Riedel and P-shear geometries that are compatible with left-lateral slip on the Magallanes-Fagnano fault-zone. Strike-slip and normal faults occur in a releasing step-over between two overlapping left-lateral, left-stepping segments of the Magallanes fault zone and record a tectonic event defined by sinistral transtension that probably reflects changing plate dynamics associated with the opening of the Drake Passage during the Early Miocene.

Return to top | Return to Index


COMPRESSIBILITY AND PERMEABILITY OF GULF OF MEXICO MUDROCKS, RESEDIMENTED AND IN-SITU

William Salter Betts, MSGeoSci

University of Texas at Austin, Month Year

Supervisor: May 2014

123 pages, 89 references, 6 tables

Uniaxial consolidation tests of resedimented mudrocks from the offshore Gulf of Mexico reveal compression and permeability behavior that is in many ways similar to those of intact core specimens and field measurements. Porosity (n) of the resedimented mudrock also falls between field porosity estimates obtained from sonic and bulk density well logs at comparable effective stresses.

Laboratory-prepared mudrocks are used as testing analogs because accurate in-situ measurements and intact cores are difficult to obtain. However, few direct comparisons between laboratory-prepared mudrocks, field behavior, and intact core behavior have been made. In this thesis, I compare permeability and compressibility of laboratory-prepared specimens from Gulf of Mexico material to intact core and field analysis of this material.

I resediment high plasticity silty claystone obtained from Plio-Pleistocene-aged mudrocks in the Eugene Island Block 330 oilfield, offshore Louisiana, and characterize its compression and permeability behavior through constant rate of strain consolidation tests. The resedimented mudrocks decrease in void ratio (e) from 1.4 (61% porosity) at 100 kPa of effective stress to 0.34 (26% porosity) at 20.4 MPa. I model the compression behavior using a power function between specific volume (v=1+e) and effective stress (σ’v):

v=1.85σ’v-0.108

Vertical permeability (k) decreases from 2.5•10-16 m2 to 4.5•10-20 m2 over this range, and I model the permeability as a log-linear function of porosity (n):

log10k=10.83n-23.21

Field porosity estimates are calculated from well logs using two approaches; an empirical correlation based on sonic velocities, and a calculation using the bulk density. Porosity of the resedimented mudrock falls above the sonic-derived porosity and below the density porosity at all effective stresses. Measurements on intact core specimens display similar compression and permeability behavior to the resedimented specimens. Similar compression behavior is also observed in Ursa Basin mudrocks. Based on these similarities, resedimented Gulf of Mexico mudrock is a reasonable analog for field behavior.

Return to top | Return to Index


FOSSILS, PHYLOGENY, AND ANATOMICAL REGIONS : INSIGHTS EXEMPLIFIED THROUGH TURTLES

Robert Wayne Burroughs, M.S.Geo.Sci.

University of Texas at Austin, August 2013

Supervisor: Christopher J. Bell

301 pages, 117 references

There are more than 300 species of extant turtles, the majority of which belong to the Testudinoidea. Here I describe a new box turtle from the Eocene-Oligocene boundary of west Texas. This specimen impacts the phylogeny of Testudinoid turtles by pulling the divergence of extant Testudinoid turtles back in time approximately 25 million years. This results in a need to refocus on paleontological research of Testudinoid turtles into the late Paleogene and early Neogene to identify fossil localities and specimens that can help further elucidate the evolution of the group. New work on the fossil record of turtles also requires a re-evaluation of methods used for identifying and evaluating the evolutionary history of turtles as a group. An implicit assumption over the last 150 years of turtle paleontology was that both turtle shells and turtle heads reveal congruent and complimentary evolutionary relationships. This assumption was never adequately tested. I utilized a series of methods to evaluate the congruency of phylogenetic hypotheses using disparate anatomical regions. Using a dataset of extant Emydid turtles, I evaluated whether turtle shells and turtle heads provided congruent and complimentary phylogenetic hypotheses. My methods employed parsimony-based reconstruction, maximum-likelihood-based reconstruction, and Bayesian-based reconstruction, including Bayesian-partition analyses. My conclusions are that heads and shells do not provide fully congruent topologies, and that in many cases there is a loss of phylogenetic resolution when only turtle sklls are used to generate phylogenies. The implication is that a focus on a robust and complete dataset of anatomical features will provide the best basis for further investigation of fossils. My work also provides a framework for dataset exploration by providing a method to identify the most robust phylogenetic signal found within a dataset. This framework will allow non-turtle paleontologists and systematists the ability to further investigate their own datasets and develop robust hypotheses of evolutionary relationships across the diversity of the tree of Life.

Return to top | Return to Index


STRUCTURAL AND STRATIGRAPHIC EVOLUTION OF THE WEEPAH HILLS AREA, NV - TRANSITION FROM BASIN-AND-RANGE EXTENSION TO MIOCENE CORE COMPLEX FORMATION

Joshua Bruce Burrus, M.S.Geo.Sci.

University of Texas at Austin, May 2013

Supervisor: Daniel Stockli

104 pages, 90 references, 5 tables

The Weepah Hills Area (Nevada) exposes exhumed metamorphic and plutonic rocks and upper-plate (supradetachment) volcano-sedimentary rocks that have experienced a complex, multi-stage deformational and depositional history. The Weepah Hills metamorphic core complex (WHMCC) is located in a region of the western Cordillera that was affected by both Miocene Basin-and-Range style E-W extension and Mio-Pliocene Walker Lane transcurrent shearing. Mio-Pliocene transcurrent deformation is transferred across a ~175 km releasing bend, known as the Mina Deflection, that kinematically links dextral strike-slip faults of the Death Valley-Fish Lake Valley with the central Walker Lane Belt. Progressive Mio-Pliocene transtension is characterized by core complex detachment faulting and younger high-angle normal faults. Timing of detachment faulting is constrained by both (U-Th)/He thermochronometry of footwall rocks and detailed chronostratigraphy of upper-plate strata to between 9-6 Ma. This age is supported by deformation recorded in the upper-plate strata that is attributed to progressive folding of the detachment associated with corrugation development. Earlier Miocene Basin-and-Range style extension is characterized by N-S trending high-angle normal faults and half-grabens that are strongly overprinted by Mio-Pliocene structures. (U-Th)/He zircon cooling ages from the detachment footwall range from ~12-20 Ma and are attributed to exhumation and unroofing related to E-W Basin-and-Range extension. New detailed sedimentological and geochronologic data show that, in contrast to previous research, the WHMCC upper-plate strata do not form a single supradetachment package, but rather three temporally distinct Miocene stratigraphic packages bounded by angular unconformities. The stratigraphic, structural, and exhumational record preserved in the WHMCC elucidates the timing of deformation and sedimentary basin evolution related to both Basin-and-Range E-W extension and Walker Lane related NW-directed transtension.

Return to top | Return to Index


CONSTRAINTS FROM MANTLE XENOLITHS ON THE GEODYNAMIC EVOLUTION OF EARTH'S UPPER MANTLE

Benjamin Lee Byerly, PhD

University of Texas at Austin, May 2014

Supervisor: John C. Lassiter

194 pages, 189 references, 6 tables

Geophysical studies identify a region of slow seismic velocity mantle beneath the central Rio Grande rift that potentially represents a region of hot asthenospheric mantle that has replaced destabilized lithosphere. We determine that the majority of mantle xenoliths from Elephant Butte on the central Rio Grande rift axis are, based on their geochemical affinity to depleted mantle, derived from asthenospheric mantle that has accreted to the base of the Proterozoic lithosphere. Using mantle heat flow models, we estimate the boundary between residual lithosphere and accreted asthenosphere to be at ~45km depth. The amount of lithosphere thinning that has occurred cannot be accounted for by rift-related extension and we therefore suggest that convective removal of a large portion of Proterozoic lithosphere has occurred.

Convecting upper mantle-derived peridotites display extreme isotopic depletions that are not observed in mid-ocean ridge basalts (MORB). Previous studies suggest that these isotopically ultradepleted domains represent rare refractory mantle domains that do not participate in MORB petrogenesis. We demonstrate the isotopically ultradepleted domains are not only a ubiquitous feature of convecting upper mantle, but are also capable of melting if advected beneath mid-ocean ridges. To explain the lack of MORB with ultradepleted isotopes, we suggest that MORB compositions are biased towards fertile enriched source components. Estimates of upper mantle composition based on MORB therefore overestimate the fertility of the upper mantle.

The Lu-Hf system is commonly used to estimate the timing of melt depletion events in the lithospheric mantle. This is typically done with pseudoisochrons from genetically related mantle xenoliths. Most studies, however, misinterpret Lu/Hf – Hf isotopes correlations by using Cpx Lu/Hf ratios when whole rock Lu/Hf ratios are appropriate due to equilibration above the Lu-Hf closure temperature. Hafnium isotopes do not typically correlate with indicators of melt depletion, which suggests that Hf isotopes do not record ancient melting events. This is likely due to overprinting of Hf isotopes by later metasomatic events.

Return to top | Return to Index


THE INFLUENCE OF THE PERMIAN SYNDEPOSITIONAL FRACTURE NETWORK ON THE MODERN GEOMORPHOLOGY AT SLAUGHTER CANYON, NEW MEXICO

Jason Neal Camacho, ASc.

University of Texas at Austin, December 2013

Supervisor: Charles Kerans

47 pages, 37 references, 3 tables

The Guadalupe Mountains are a widely recognized field laboratory for carbonate geology. They are also analogous to the prolific West Texas Field. Preferential regional-scale trellis style weathering patterns driven by Syndepositional deformation exist throughout the southeastern front of the Guadalupe Mountains. This study examines the relationship between the anomalous outcrop scale high-relief elongate fin structures in the mouth of Slaughter Canyon and preferential erosion related to the differential incidence of Syndepositional fractures. This relationship was investigated by integrating traditional field controlled fracture mapping with a remote survey done via digital outcrop model to quantify the frequency and incidence of the fracture network at the mouth of Slaughter Canyon, NM.

After field and remote surveys were conducted, built-for-purpose fracture diagnostic software using a normalized correlation count was implemented in the analysis. Results show that there is an inverse relationship between high density zones of deformation and the fin structures and an average syndepositional fracture density of ~28 m in the gullies and ~14 m in the fins. This ratio is smaller than that observed elsewhere in the Guadalupe Mountains. This smaller ratio could be the driver behind the high relief erosional fins that are prevalent on the south western wall of Slaughter Canyon.

Return to top | Return to Index


CORRECTION FOR DISTORTION IN POLARIZATION OF REFLECTED SHEAR-WAVES IN ISOTROPIC AND ANISOTROPIC MEDIA

Terence A Campbell, Ph.D.

University of Texas at Austin, December 2013

Supervisor: Robert H. Tatham

177 pages, 75 references, 5 tables

The progressive growth of onshore shale production (both gas and liquids) to replace depleting and aging oil fields may benefit from the use of surface seismic shear wave data analysis for full characterization of shale reservoir properties and lead to optimum development of these resources. This includes descriptions of azimuthal anisotropy (HTI - transverse isotropy with a horizontal symmetry axis) for characterization of fractures and internal fracture systems. The objective of this study is to document a predicted distortion in polarization of propagating seismic shear waves upon reflection at a subsurface interface and to propose a correction to this distortion. The polarization distortion occurs even in wholly isotropic media. This correction is based on an understanding of shear amplitude behavior as a function of the reflection incidence angle, particularly differences in the reflection angle relation for different shear components. This includes demonstration of the efficacy of the proposed correction by applying it to simulated and real direct shear-wave source data. Such corrections should result in a minimized polarization in the reflection process. The apparent consistency of a null value (zero crossing) of the SV-SV reflectivity (near 20-24 degrees) for common density and velocity contrasts as well as the remarkably regular behavior of the SV-SV reflectivity curve following a linear relation in sin2 and tan2 of the incidence angle and offers the opportunity for a simple and stable correction with minimal sensitivity to detailed knowledge of contrasts in velocity and density. The only independent information required for the correction is the angle of incidence where the SV-SV and SH-SH reflections vanish and the range of these angles is typically quite limited. Some key questions must be addressed in gaining an understanding of shear wave polarization distortion upon reflection for varying model data: 1) how do we address reflected polarization distortion for purely isotropic medium for varying incidence angles? 2) How do we apply this correction for an isotropic and anisotropic media for both simulated and actual field data 3) How do we address applications to real data and how distorted amplitudes can be corrected to identify actual subsurface HTI anisotropy.

Significantly, the polarization distortion correction is implemented as a simple extension of the established Alford rotation for normal incidence shear reflections of varying polarization. This extension leads to the improved analysis of direct shear-source 3D data with inherently distorted polarization. Thus, analysis may be applied to estimate HTI anisotropy previously not realizable in finite offset data subject to polarization distortion. Example applications to actual field data are included.

Note that the polarization correction does remove the AVO effects often exploited in analysis of P-P data where polarization is not an issue and to SV-SV and SH-SH oriented direct shear-wave profiles. Further, additional analysis of the polarization correction on field data with documented anisotropy will be required to fully develop the usefulness of this proposed correction.

Return to top | Return to Index


BASIN DEPTH CONTROL ON THE FLUVIAL AUTOGENIC PROCESSES OF DELTAIC SYSTEMS

Brandee Carlson, Bachelor of Science

University of Texas at Austin, December 2013

Supervisor: Wonsuck Kim

26 pages, 12 references, 1 table

Autogenic processes are inherent processes in sediment transport that influence landscape building and leave distinct signatures in the sedimentary record. It is of great interest to understand autogenic processes better in order to clearly decouple the stratigraphic products generated by external controls (e.g., tectonics or climate change) from internal dynamics. Here we present results from a series of delta-building experiments designed to determine the response of the fluviodeltaic autogenic timescales and processes to varying basin water depth. These internal dynamics have a characteristic timescale that is required for the delta topset to be reworked through a full cycle of storage and release of sediment. The topset aggrades by fluvial sedimentation until it reaches a maximum slope, at which point a large amount of sediment is released, typically via a strong channelization. This is followed by a period of channel migration, avulsion, and backfilling, and the cycle is repeated. We used time-lapse images to track shoreline positions and observe changes in progradation rate. The experimental results indicate that the autogenic timescale generally increases with increasing basin water depth. These observations may be explained by the amount of time required to build a lobe with an area large enough to trigger a switch from a lobe-building release event to a backfilling storage event. Each deposit was allowed to prograde to the same length of 1m to ensure that topset area was consistent and that basin depth was an isolated variable between experiments. Individual lobes show a similar average surface area regardless of basin depth in the experiments. Deeper basin depth simply requires a larger volume to be filled within this area, thus more time to complete one autogenic process. However, when channel depth is significantly smaller than basin depth, e.g., in very deep basins, stochastic variability in sediment transport and channel lateral mobility outweighs the autogenic cyclicity. Basin depth also seems to control the width and elongation of individual lobes due to channel geometry and lateral migration. Shallower basin depths are more conducive to lateral migration during lobe building, resulting in wider lobes. Deeper basin depth allows less lateral migration, resulting in more elongate lobe building. This study suggests that internal dynamics controls the shape and size of the lobe stratigraphic building unit in fluviodeltaic systems and can be useful to interpret relative basin depth at the time of deposition.

Return to top | Return to Index


CARBON DIOXIDE STORAGE IN GEOLOGICALLY HETEROGENEOUS FORMATIONS

Kyung Won Chang, Ph.D.

University of Texas at Austin, December 2013

Supervisors: Marc A. Hesse and Jean-Philippe Nicot

180 pages, 156 references, 9 tables

Geological carbon dioxide (CO2) storage in deep geological formations can only lead to significant reductions in anthropogenic CO2 emissions if large amounts of CO2 can be stored safely. Determining the storage capacity, which is the volume of CO2 stored safely, is essential to determine the feasibility of geological CO2 storage. One of the main constraints for the storage capacity is the physical mechanisms of fluid flow in heterogeneous formations, which has not been studied sufficiently. Therefore, I consider two related problems: a) the evolution of injection-induced overpressure that determines the area affected by CO2 storage and b) the rate of buoyant fluid flow along faults that determines the leakage of CO2. I use a layered model of a sandstone reservoir embedded in mudrocks to quantify the increase in storage capacity due to dissipation of overpressure into the mudrocks. I use a model of a fault surface with flow barriers to constrain the reduction in the buoyancy-driven leakage flux across the fault.

Using the layered model with injection at constant rate, I show that the pressure evolution in the reservoir is controlled by the amount of overpressure dissipated into ambient mudrocks. A main result of this study is that the pressure dissipation in a layered reservoir is controlled by a single dissipation parameter, M, that is identified here for the first time. I also show that lateral pressure propagation in the storage formation follows a power-law governed by M. The quick evaluation of the power-law allows a determination of the uncertainty in the estimate of the storage capacity. To reduce this uncertainty it is important to characterize the petrophysical properties of the mudrocks surrounding the storage reservoir. The uncertainty in mudrock properties due to its extreme heterogeneity or limited data available can cause large variability in these estimates, which emphasizes that careful characterization of mudrock is required for a reliable estimate of the storage capacity. The cessation of the injection operation will reduce overpressure near the injector, but regional scale pressure will continue to diffuse throughout the whole formation. I have been able to show that the maximum radius of the pressure plume in the post-injection period is approximately 3.5 times the radius of the pressure plume at the cessation of injection.

Two aquifers can be hydraulically connected by a fault cutting across the intermediate aquitard. If the upper aquifer contains denser fluid, an exchange flow across the fault will develop. The unstable density stratification leads to a fingering pattern with localized zones of upwelling and downwelling along the fault. Due to the small volume of the fault relative to the aquifers, the exchange-flow will quickly approach a quasi steady state. If the permeability of the fault plane is homogeneous, the average number of the quasi-steady plume fingers, ‹ν›, scales with the square root of the Rayleigh number Ra and the exchange flux measured by dimensionless convective flux, the Sherwood number, Sh, is a linear function of Ra. The dispersive flux perpendicular to the flow direction induces the formation of wider fingers and subsequently the less convective flux parallel to the flow direction. In the flow system with larger Ra, even the same increase in transverse dispersivity αΤ causes stronger impact of the mechanical dispersion on the vertical exchange flow so that ‹ν› and Sh reduce more with larger αΤ. Both measured characteristics, however, follow the same scaling for the non-dispersive homogeneous case by using a modified Rayleigh number, Ra*, considering the mechanical dispersion. The presence of flow barriers along the fault triggers unsteady exchange flow and subsequently controls the growth of the plume fingers. If the barriers are sufficiently wide to dominate the flow system, they create preferential pathways for exchange flow that determines the distribution of the quasi-steady fingers, and ‹ν› converges to a constant value. In addition, wider barriers induce substantial lateral spreading and enhance the efficiency of structural trapping, and reduce the exchange rate but still follows a linear relationship function of the effective Rayleigh number, Raeff, defined by the vertical effective permeability.

This study is motivated by geological CO2 storage in brine-saturated aquifer, but the effect of geological heterogeneity is also important in many other geological and engineering applications, in particular the risk assessment of the injection operations or the migration of hydrocarbons in tectonic-driven or hydraulically developed faults in reservoirs. Better understanding of fluid flow in geologically heterogeneous formations will allow more precise estimate of the reservoir capacity as well as more efficient operation of injection or production wells.

Return to top | Return to Index


SEISMIC DIFFRACTION IMAGING METHODS AND APPLICATIONS

Luke Adam Decker, M.S.

University of Texas at Austin, May 2014

Supervisor: Sergey Fomel

108 pages, 86 references

Seismic waves can either be reflected or diffracted by subsurface objects depending on the object's geometry. Diffactions can be used to determine details about the small-scale features that generate them, such as karsts, voids, pinchouts, faults, fractures, and salt flanks. Diffraction imaging can have resolution below the typical seismic wavelength. Scattered waves are recorded as significantly lower-energy signal than reflected waves, requiring that diffractions be separated from reflections. I describe three methods of such separation: data-domain plane-wave destruction, Fresnel zone Elimination, and partial-image plane-wave destruction. Once separated, diffractions can be migrated to create a seismic diffraction image and used in velocity analysis.

Common-reflection angle migrated diffractions appear flat in dip angle gathers when migrated with correct velocity. I illustrate how this property can be used to determine migration velocity through a process of oriented velocity continuation (OVC). In OVC framework diffraction data are decomposed by slope and migrated over a range of velocities. Velocities corresponding to the flattest slope gathers are picked using semblance as a measure of flatness. This provides an estimate of migration velocity. Stacking gathers corresponding to this chosen velocity generates a seismic diffraction image.

Seismic diffraction images provide interpreters with information about small-scale geologic objects that may not be available in conventional images. Scattering features that are interesting for exploration, like voids, caves, fractures, and faults, cause diffractions and can be resolved with better focus in diffraction images than in conventional ones. This is particularly useful with geologically complex carbonate systems. Carbonates are strongly heterogeneous, making them difficult to image with conventional methods. Reservoir porosity is often contained within caves, or small vugs. These features are difficult to characterize with conventional methods because cave reflections have large geometric uncertainties in cave size and location. Velocity analysis of seismic reflection data in carbonates may not highlight vugular porosity particularity well. I illustrate how diffraction images provide improved characterization by highlighting the edges of caves, thus constraining cave geometry, and highlighting more heterogenous zones by measuring the amount of scattering those zones generate.

Return to top | Return to Index


PHYSICAL MODELS OF TSUNAMI DEPOSITION : AN INVESTIGATION OF MORPHODYNAMIC CONTROLS

Katherine Lynn Delbecq MSGeoSci

University of Texas at Austin, May 2013

Supervisors: Wonsuck Kim and David Mohrig

37 pages, 44 references, 2 tables

A key goal of tsunami research is to quantitatively reconstruct flow parameters from paleotsunami deposits in order to better understand the geohazards of coastal areas. These reconstructions rely on grain-size and thickness measurements of tsunami deposits, combined with simple models that allow an inversion from deposit characteristics to wave characteristics. I conducted flume experiments to produce a data set that can be used to evaluate inversion models for tsunami deposition under controlled boundary conditions. Key variables in the flume experiments are sediment grain-size distribution, flow velocity and depth, and depth of water ponded in the flume before the tsunami bore was released. Physical experiments were run in a 32 m-long outdoor flume at The University of Texas at Austin. The flume has a head box with a specialized mechanical lift gate that allows instantaneous release of water to create a bore. Various sediment mixtures (silt to very coarse sand) are introduced to the upstream end of the channel as a low dune positioned just below the lift gate. The bore entrained the sediment mixture, producing an unambiguous suspension-dominated deposit in the downstream half of the channel. Deposits were sampled for grain-size and thickness trends. The experimental results capture characteristics of many recent and paleotsunami deposits, including consistent fining in the transport direction. In addition to overall fining, trends in deposit sorting and coarse (D95) and fine (D10) fractions reveal the importance of sediment-source grain-size distribution on tsunami deposit attributes.

Return to top | Return to Index


TRANSIENCE OF A POTENTIAL GEOTHERMAL FLUX ALY BENEATH A TRIBUTARY ICE STREAM OF THWAITES GLACIER, WEST ANTARCTICA

John Boone DeSanto, B.S.

University of Texas at Austin, May 2013

Supervisor: Donald Blankenship

34 Pages, 21 references, 1 table

The Amundsen Sea Embayment of the West Antarctic ice sheet (WAIS) is currently one of the most rapidly changing sectors of a continental ice sheet. As a marine ice sheet, the WAIS is in a potentially unstable configuration. A model is proposed to evaluate the effect of geothermal flux on flow in ice streams using ice layer drawdown anomalies, features identifiable by a thick layer package resting on top of deformed ice. Drawdown anomalies represent either significant loss or mechanical deformation of basal ice.

Several features with the geometry of drawdown anomalies are identi¬fied in Thwaites Glacier along an ice stream tributary near Mt. Takahe. These anomalies correlate with the surface ice velocity and have thick layer packages age at a constant rate, implying deformation at a single origin corresponding to an upstream edifice. The abnormal amplitude of upstream drawdown anomalies implies a thermal event at the same edifice 1000-2000 years ago. This provides another example of high heterogeneous geothermal flux in the WAIS.

Return to top | Return to Index


TIME-LAPSE SEISMIC MONITORING FOR ENHANCED OIL RECOVERY AND CARBON CAPTURE AND STORAGE FIELD SITE AT THE CRANFIELD FIELD, MISSISSIPPI

Julie Nicole Ditkof, M.S. Geo. Sci.

University of Texas at Austin, December 2013

Supervisors: Nathan Bangs and Timothy A. Meckel

111 pages, 93 references, 13 tables

The Cranfield field, located in southwest Mississippi, is an enhanced oil recovery and carbon sequestration project that has been under a continuous supercritical CO2 injection by Denbury Onshore LLC since 2008. Two 3D seismic surveys were collected in 2007, pre-CO2 injection, and in 2010 after › 2 million tons of CO2 was injected into the subsurface. The goal of this study is to characterize a time-lapse response between two seismic surveys to understand where injected CO2 is migrating and to map the injected CO2 plume edge.

In order to characterize a time-lapse response, the seismic surveys were cross equalized using a trace-by-trace time shift. A normalized root-mean-square (NRMS) difference value was then calculated to determine the repeatability of the data. The data were considered to have "good repeatability," so a difference volume was calculated and showed a coherent seismic amplitude anomaly located through the area of interest. A coherent seismic amplitude anomaly was also present below the area of interest, so a time delay analysis was performed and calculated a significant added velocity change. A Gassmann-Wood fluid substitution workflow was then performed at two well locations to predict a saturation profile and observe post-injection expected changes in compressional velocity values at variable CO2 saturations. Finally, acoustic impedance inversions were performed on the two seismic surveys and an acoustic impedance difference volume was calculated to compare with the fluid substitution results. The Gassmann-Wood fluid substitution results predicted smaller changes in acoustic impedance than those observed from acoustic impedance inversions.

At the Cranfield field, time-lapse seismic analysis was successful in mapping and quantifying the acoustic impedance change for some seismic amplitude anomalies associated with injected CO2. Additional well log data and refinement of the fluid substitution workflow and the model-based inversion performed is necessary to obtain more accurate impedance changes throughout the field instead of at a single well location.

Return to top | Return to Index


SHELF-EDGE DELTAS : STRATIGRAPHIC COMPLEXITY AND RELATIONSHIP TO DEEP-WATER DEPOSITION

Joshua Francis Dixon, PhD

University of Texas at Austin, May 2013

Supervisor: Ronald J. Steel

217 pages, 139 references, 4 tables

This research investigates the character and significance of shelf-edge deltas within the sedimentary source-to-sink system, and how variability at the shelf edge leads to different styles of deep-water deposition. Because the shelf-edge represents one of the key entry points for terrigenous sediment to be delivered into the deep water, understanding of the sedimentary processes in operation at these locations, and the character of sediment transported through these deltas is critical to understanding of deep-water sedimentary systems. The research was carried out using three datasets: an outcrop dataset of 6000 m of measured sections from the Permian-Triassic Karoo Basin, South Africa, a 3D seismic data volume from the Eocene Northern Santos Basin, offshore Brazil and a dataset of 29 previously published descriptions of shelf-edge deltas from a variety of locations and data types.

The data presented highlight the importance of sediment instability in the progradation of basin margins, and deep-water transport of sediment. The strata of the Karoo Basin shelf margin represent river-dominated delta deposits that become more deformed as the shelf-edge position is approached. At the shelf edge, basinward dipping, offlapping packages of soft-sediment-deformed and undeformed strata record repetitive collapse and re-establishment of shelf-edge mouth bar packages. The offlapping strata of the Karoo outcrops record progradation of the shelf margin through accretion of the shelf-edge delta, for over 1 km before subsequent transgression. The Eocene Northern Santos Basin shelf margin, in contrast, exhibits instability features which remove kilometers-wide wedges of the outer shelf that are transported to the basin floor to be deposited as mass-transport packages. In this example, shelf-edge progradation is achieved through ‘stable’ accretion of mixed turbidites and contourites.

The data also emphasize the importance of the role of shelf-edge delta processes in the delivery of sediment to the basin floor. A global dataset of 29 examples of shelf-edge systems strongly indicates that river domination of the shelf-edge system (as read from cores, well logs or isopach maps) serves as a more reliable predictor of deep-water sediment delivery and deposition than relative sea level fall as traditionally read in shelf-edge trajectories or sequence boundaries.

Return to top | Return to Index


RELATIVE VALUATIONS OF MERCHANT AND TOLLING LNG MODELS CONSIDERING ALTERNATE CAPITAL STRUCTURES

Michael Addington Drummond, M.B.A., M.S.E.E.R.

University of Texas at Austin, December 2013

Supervisors: David B. Spence and James S. Dyer

82 pages, 24 references

As recently as 2008 liquefied natural gas (LNG) import facilities were being constructed in the United States in order to help meet domestic demand. Within the past five years, the development of hydraulic fracturing has created a seismic shift in the energy landscape as companies are turning their focus to exporting LNG instead of importing it. Today, there are currently more than twenty liquefaction facilities awaiting regulatory approval to export domestic product to non-Free Trade Agreement nations. As of November 2013, regulators have approved export capacity of approximately 2,300 billion cubic feet per year, a figure which could rise dramatically over the next decade. Clearly the shale revolution, which has suppressed domestic natural gas prices relative to European and Asian markets, has created an intriguing arbitrage opportunity. The risks to LNG asset owners, however, are high. Long-term domestic and regional prices are uncertain, and capital expenditure costs require a heavy debt burden.

We will examine two primary LNG contract structures with altering project financing considerations. The first is the merchant model, in which the LNG asset owner takes title to the supply. The second is the tolling model, in which the LNG asset owner does not take title to the supply. Each of these scenarios will be valued using a high debt, low equity capital structure and a medium debt, medium equity capital structure. Once we have determined the relative valuations of each scenario, sensitivity analysis and Monte Carlo methods will be applied to the outcomes in order to determine the optimal combination of contract structure and capital structure for both debt and equity holders.

Return to top | Return to Index


THE NORTHEASTERN GULF OF MEXICO : VOLCANIC OR PASSIVE MARGIN? SEISMIC IMPLICATIONS OF THE GULF OF MEXICO BASIN OPENING PROJECT

Mark Hamilton Duncan, MS Geosciences

University of Texas at Austin, May 2013

Supervisors: Gail Christeson, Harm Van Avendonk

80 pages, 47 references, 1 table

The Gulf of Mexico Basin Opening project (GUMBO) is a study of the lithological composition and structural evolution of the Gulf of Mexico (GoM) that uses Ocean Bottom Seismometer (OBS) data from four transects in the Northern GoM. I examine 39 OBS shot records in the easternmost transect for shear wave arrivals and pick shear wave travel times from the 11 usable records. I then carry out a tomographic inversion of seismic refraction travel times. I use the resulting shear-wave velocity model in conjunction with a previously constructed P-wave model to examine the relationship between Vp and Vs. I compare velocities in the sediment and basement with empirical velocities from previous studies for the purpose of constraining lithological composition below the transect and make an interpretation of the structural evolution of the eastern GoM.

The seismic velocities for crust landward of the Florida Escarpment are consistent with normal continental crust. Seaward of the Escarpment, velocities in the upper oceanic crust are anomalously high (Vp = 6.5 – 7 km/sec; Vs = 4.0 – 4.6 km/sec). A possible explanation for this observation is that GoM basalt formation consisted of basaltic sheet flows, forming oceanic crust that does not contain the vesicularity and lower seismic velocities found in typical pillow basalts. Increased magnesium and iron content could also account for these high velocities.

Seismic refraction and reflection data provide a means of investigating the nature of the Moho in the northeastern GoM. I use a finite difference method to generate synthetic record sections for data from eight instruments that are part of the two easternmost GUMBO seismic lines (lines 3 & 4). I then vary the thickness of the Moho in these synthetic models and compare the results with the original receiver gather to examine the effects this variability has on amplitudes.

The data from the instruments chosen for these two lines are representative of continental and transitional crust. The finite difference models indicate that the Moho beneath GUMBO 3 is ~1500 m thick based on the onset and amplitudes of PmP arrivals. All five instruments display consistent results. The instruments along GUMBO 4 suggest a Moho almost twice as thick as GUMBO 3 on the landward end of the transect that grades into a Moho of similar thickness (1750 m) in the deep water GoM. The three instruments used to model the Moho in this area show that the Moho ranges from ~1750 to 3500 m in thickness. The sharper boundary beneath continental crust in GUMBO Line 3 supports other evidence that suggests magmatic underplating and volcanism in the northern GoM during the mid-Jurassic. The thicker Moho seen on the landward end of GUMBO Line 4 that is overlain by continental crust was likely unaffected by GoM rifting. Therefore, the Moho beneath the Florida Platform might be as old as the Suwannee Terrane, and complex Moho structure is not uncommon for ancient continental crust.

Return to top | Return to Index


SEISMIC GEOMORPHOLOGY OF THE SAFI HAUTE MER EXPLORATION BLOCK, OFFSHORE MOROCCO’S ATLANTIC MARGIN

Dallas Brogdon Dunlap, M.S. Geo. Sci.

University of Texas at Austin, December 2013

Supervisor: Lesli J. Wood

111 pages, 66 references

The lower continental slope of Morocco’s west coast consists of Triassic-age salt manifested in the form of diapirs, tongues, sheets, and canopies, and both extensional and compressional structures that result from salt movements. Salt diapirism and regional tectonics greatly influenced a broad spectrum of depositional processes along the margin. Mapping of a 1064-km2 (411-mi2) seismic survey acquired in the Safi Haute Mer area reveals that Jurassic to Holocene salt mobilization has induced sedimentation that manifests itself in gravity slumps and slides and debris flows. An east-west–trending structural anticline located downdip of the salt-influenced region, was activated during the Atlas uplift (latest Cretaceous) and shaped much of the lower continental slope morphology from Tertiary time until present. The largest of the mass transport deposits (MTC) is a 500-m (1640-ft)-thick Cretaceous-age unit that spans an area of up to 20,000 km2 (7722 mi2). Seismic facies composing the MTC are (1) chaotic, mounded reflectors; (2) imbricated continuous to discontinuous folded reflector packages interpreted to represent internal syn-depositional thrusts; and (3) isolated, thick packages of continuous reflectors interpreted to represent transported megablocks (3.3 km2 [1.3 mi2]). The latter show well preserved internal stratigraphy. The MTCs originated from an upslope collapse of a narrow shelf during the earliest phases of the Alpine orogeny.

Seismic geomorphologic analysis of the non-salt-deformed sections reveal numerous linear features that are interpreted as migrating Mesozoic-age deepmarine sediment waves. Three styles of sediment waves have been identified. These include: (1) type J1—small (less than 17 m thick) and poorly imaged, Jurassic in age, ridges that have wavelengths of up to 12 km and crest-to-crest separations of less than 1 km; (2) type K1—early Aptian constructional sediment waves (~110 m thick) that appear to show some orientation and size variations which suggest an influence on currents by salt-influenced seafloor topography, and (3) type K2—latest Albian and earliest post-Albian sediment waves exhibiting wave heights of 40 m and crest-to-crest separations of 1 km, that are continuous across the entire study area and show evidence of up-slope migration.

Return to top | Return to Index


WATER USE BY THE OIL AND GAS INDUSTRY : AN ASSESSMENT OF TWO TEXAS REGIONS

Jeanne Lynn Eckhart, M.S. E.E.R.

University of Texas at Austin, December 2013

Supervisor: William L. Fisher and Jean-Philippe Nicot

82 pages, 60 references, 2 tables

The oil and gas industry makes up approximately 1% of Texas’s overall water use (TWDB, 2012), but assessing water use on a regional and county level could show that the impacts from the oil and gas industry can be greater on a local level. Water planners within in Texas are becoming more concerned with how regional and local impacts from upstream development of oil and gas. These areas are under water-stressed conditions due to drought. To better understand potential local use impacts this study conducted qualitative and quantitative analyses. The qualitative analysis gathered input from stakeholders including representatives in the oil and gas industry, regulatory sector, and Texas water planning entities. This study utilized two public databases called FracFocus to assess average water use trends over time for the Eagle Ford region in south Texas and the Spraberry/Wolfcamp formations in west Texas.

According to the qualitative analysis conducted trends toward increasing use of brackish groundwater and some recycling and reuse techniques by some operators are occurring in both regions. Also, there were slightly increasing trends of average water use per a well over time for both regions between January 2011 and April 2013. This analysis can be misrepresentative of the cause of the change in water use by the oil and gas industry, and therefore requires more data. The FracFocus database lacks the direction of the well, the lateral length of the well, and the mass of the proppant. These inputs would allow for a holistic analysis by water planners.

The oil and gas industry can have local impacts on water use in particular regions. An increasing importance for regional water planners to have access to accurate oil and gas water use data is apparent. Collaboration between the oil and gas industry and Texas regional water planners will be a key component in areas with heavier mining water demands. Conclusively, the need for a more robust data set for regulators, industry professionals, and other stakeholders to access will benefit the strategic assessments oil and gas water use on local levels.

Return to top | Return to Index


ROLE OF RAIN GARDENS AND VEGETATED RETENTION PONDS IN REDIRECTING STORMWATER RUNOFF INTO EVAPORATION OR RECHARGE IN DOWNTOWN AUSTIN, TEXAS

Audrey Eljuri, Bachelor of Science

University of Texas at Austin, May 2014

Supervisor: Kevan B. Moffett

56 pages, 38 references, 10 tables

The city of Austin, Texas is investing money into aesthetic stormwater structures such as rain gardens and vegetated retention ponds to reduce stormwater runoff, erosion, and flood risks. Flood events are a growing concern in a growing urbanized city like Austin because an increase in urbanization (i.e., asphalt) equates to more runoff and therefore increased flooding. Residential rain gardens are expected to catch and contain water that falls on the adjacent roof and into the garden, which either leaves as discharge out of the root zone or evapotranspiration from the rain garden. The vegetated retention pond is expected to reduce the length of ponding compared to a standard retention pond with no vegetation.

To analyze the effectiveness of these structures, the water balance equation was quantified for two rain gardens, a control garden, a vegetated retention pond, and a traditional retention pond. Soil moisture sensors were installed at each field site to monitor soil moisture and a rain gage to monitor precipitation. Assuming no runoff out of any of the structures, almost all of the water volume input into the field sites left the root zone as deep drainage. Rain garden 2 had dried out the fastest after a rain event compared to all the other sites. Soil moisture in the retention pond remained within 5% of the maximum volumetric moisture resulting in hours of ponding after a storm event. Vegetation in retention ponds reduced the extent of ponding.

ArcGIS was used to show the extent of stormwater runoff to local creeks in the West Bouldin Creek watershed, where all five field sites were located, to see how flood extent would change if different amounts of rain gardens were installed in the watershed. A previous flood event from October 30th to 31st, 2013, was analyzed to estimate the lateral extent of the flood along the creeks under different rain garden development scenarios. Assumptions made in this model included that all runoff that goes into a rain garden remains in the rain garden, and that the creeks have the same width, depth, and creek bank slope. The volume of water at the mouth of the watershed from the peak flow volume during the October flood event was reduced 4.6% with 100 rain gardens installed in the watershed, 11% with 250 rain gardens installed and 23% with 500 rain gardens installed. The effects of installing a residential rain garden are minimal if evaluated individually, but with installation of several rain gardens, the reduction in flood water damage should become more apparent.

Return to top | Return to Index


PETROGENESIS OF SEVERAL SERPENTINITES WITHIN THE FRANCISCAN COMPLEX AND COAST RANGE OPHIOLITE, WESTERN CALIFORNIA

Rania Eldam, Bachelor of Science

University of Texas at Austin, May 2013

Supervisor: Jaime D. Barnes

61 pages, 98 references, 5 tables

Franciscan Complex serpentinites have been interpreted as eroded pieces of the overriding Coast Range Ophiolite (CRO), off-scraped pieces of the subducting oceanic plate off of the present California coast, and as sedimentary serpentinites (e.g., Wakabayashi, 2004); however, most of these interpretations are based on field relationships and tectonic models. This study presents bulk rock major and trace element geochemistry, pyroxene and spinel geochemistry, and stable isotope data (O, H, Cl) for serpentinite samples with the goal of determining protolith origin and subsequent serpentinizing fluid sources of several metasomatized Franciscan and CRO ultramafic rocks in order to decipher the tectonic setting of serpentinization.

This study focuses on serpentinite bodies found in the Franciscan Complex (west of Cuesta Ridge; south of San Francisco; Tiburon Peninsula; Healdsburg) (n = 12). Three samples from Cuesta Ridge (CRO) were also analyzed for comparison. All samples are >~95% serpentinized and consist of lizardite +/- chrysotile. Relict pyroxene grains are rarely preserved.

Franciscan serpentinite samples (Tiburon Peninsula, west of Cuesta Ridge) show positive-sloped REE patterns. Low LREE concentrations are typical of abyssal peridotites. Relict clinopyroxenes from Tiburon Peninsula have high HREE concentrations, also supporting an abyssal origin. Two of the three samples from the Cuesta Ridge show flat REE patterns; whereas, one is U-shaped. This high LREE concentration is similar to forearc peridotites. Spinels from Cuesta Ridge, Sawyer Camp Trail, and Mill Creek Road have Cr# › 0.60 also implying a forearc setting; whereas Franciscan localities from the Tiburon Peninsula and Highway 1 have lower Cr# (0.21 to 0.51). All samples show remarkable positive Ce and Y anomalies. We speculate that these anomalies may be due to interaction with ferromanganese nodules and crusts (also high in Ce and Y) deposited on the seafloor prior to subduction.

Cuesta Ridge samples have O values between +6.0 to +6.6‰. Franciscan serpentinites (except those south of San Francisco) have δ18O values of +5.4 to +7.9‰. These δ18O values are similar to typical oceanic serpentinites and likely represent low-T seawater hydration on the seafloor. δD values of all samples are extremely low (-107 to -90‰) and likely result from post-serpentinization, post-emplacement interaction with meteoric water at low temperature. Samples south of San Francisco lie within the San Andreas Fault zone and have high δ18O values (+7.2 to +9.5‰) and low δD values (-107 to -104‰) likely due to low-T interaction with meteoric water at high fluid-rock ratios. Most of the serpentinites (12 of the 15) have δ37C1 values between +0.2 and +0.9‰, typical values for serpentinites formed by interaction with seawater.

Based on bulk rock geochemistry and pyroxene and spinel compositions, serpentinites located within the Franciscan Complex have geochemical characteristics of abyssal peridotites; whereas, those from Cuesta Ridge are more chemically heterogeneous with most having affinity to forearc peridotites. All stable isotope geochemistry indicates seafloor serpentinization by seawater.

Return to top | Return to Index


LITHOLOGIC HETEROGENEITY OF THE EAGLE FORD FORMATION, SOUTH TEXAS

Suzan Muge Ergene, MS GeoSci

University of Texas at Austin, May 2014

Supervisor: Kitty L. Milliken

182 pages, 149 references, 28 tables

Grain assemblages in organic-rich mudrocks of the Eagle Ford Formation of South Texas are assessed to determine the relative contributions of intra- and extrabasinal sediment sources, with the ultimate goal of producing data of relevance to prediction of diagenetic pathways. Integrated light microscopy, BSE imaging, and X-ray mapping reveal a mixed grain assemblage of calcareous allochems, biosiliceous grains (radiolaria), quartz, feldspar, lithics, and clay minerals. Dominant fossils are pelagic and benthic foraminifers and thin-walled and prismatic mollusks; echinoderms, calcispheres, and oysters are present. Early-formed authigenic minerals, including calcite, kaolinite, dolomite, albite, pyrite, quartz, and Ca-phosphate, some reworked, add to the overall lithologic heterogeneity.

Point counting of images produced using energy-dispersive X-ray mapping in the SEM provides observations at a scale appropriate to classifying the mudrocks based on the composition of the grain assemblage, although grains and other crystals of clay-size cannot be fully characterized even with the SEM. Each sample is plotted on a triangle, whose vertices correspond to terrigenous and volcanic grains (extrabasinal components), calcareous allochems, and biosiliceous grains. As a subequal mix of grains of intrabasinal and extrabasinal origins the detrital grain assemblage of the Eagle Ford, presents a formidable challenge to the task of lithologic classification of this unit, as neither conventional limestone nor sandstone classifications can be readily applied. The abundant marine skeletal debris in the Eagle Ford is accompanied by abundant calcite cementation and the dissolution and replacement of biosiliceous debris is accompanied by authigenic quartz, suggesting that mudrock grain classification has potential for yielding diagenetic predictions.

Return to top | Return to Index


PORE PRESSURE WITHIN DIPPING RESERVOIRS IN OVERPRESSURE BASINS

Baiyuan Gao, M.S.Geo.Sci.

University of Texas at Austin, August 2013

Supervisor: Peter B. Flemings

87 pages, 48 references, 15 tables

A systematic study of how mudstone permeability impacts reservoir pore pressure is important to understand the regional fluid field within sedimentary basins and the control of sediment properties on subsurface pressure. I develop a 2D static model to predict reservoir overpressure from information estimated from the bounding mudstones and structural relief. This model shows that close to a dipping reservoir, the mudstone permeability is high in the up-dip location and low in the down-dip location. This characteristic mudstone permeability variation causes the depth where reservoir pressure equals mudstone pressure (equal pressure depth) to be shallower than the mid-point of the reservoir structure. Based on the 2D static model, I constructed a nomogram to determine the equal pressure depth by considering both farfield mudstone vertical effective stress and reservoir structural relief. I find the equal pressure depth becomes shallower with decreasing vertical effective stress, increasing reservoir structural relief, and increasing mudstone compressibility. Pressure predicted by the static model agrees with pressure predicted by a more complete model that simulates the evolution of the basin and is supported by field observations in the Bullwinkle Basin (Green Canyon 65, Gulf of Mexico). This study can be applied to reduce drilling risk, analyze trap integrity, and facilitate safe and efficient exploration.

Return to top | Return to Index


IMPLICATIONS FOR MONITORING CO2 LEAKAGE AT CCS SITES

Marlo Rose Gawey, M.S. Geo. Sci.

University of Texas at Austin, May 2013

Supervisors: Daniel Breecker, Katherine Romanak, Toti Larson

104 pages, 123 references, 10 tables

Perfluorocarbon tracers (PFTs) are commonly proposed tracers for use in carbon capture and sequestration (CCS) leak detection and vadose zone monitoring programs. Tracers are co-injected with supercritical CO2 and monitored in the vadose zone to identify leakage and calculate leakage rates. These calculations assume PFTs exhibit “ideal” tracer behavior (i.e. do not sorb onto or react with porous media, partition into liquid phases or undergo decay). This assumption has been brought into question by lab and field evaluations showing PFT partitioning into soil contaminants and sorbing onto clay. The objective of this study is to identify substrates in which PFTs behave conservatively and quantify non-conservative behavior. PFT breakthrough curves are compared to those of a second, conservative tracer, sulfur hexafluoride (SF6). Breakthrough curves are generated in 1D flow-through columns packed with 5 different substrates: silica beads, quartz sand, illite, organic-rich soil, and organic-poor soil. Constant flow rate of carrier gas, N2, is maintained. A known mass of tracer is injected at the head of the columns and the effluent analyzed at regular intervals for tracers at picogram levels by gas chromatography. PFT is expected to behave conservatively with respect to SF6 in silica beads or quartz sand and non-conservatively in columns with clay or organics. However, results demonstrate PFT retardation with respect to SF6 in all media (retardation factor is 1.1 in silica beads and quartz sand, 2.5 in organic-rich soil, ›20 in organic-poor soil, and ›100 in illite). Retardation is most likely due to sorption onto clays and soil organic matter or condensation to the liquid phase. Sorption onto clays appears to be the most significant factor. Experimental data are consistent with an analytical advection/diffusion model. These results show that PFT retardation in the vadose zone has not been adequately considered for interpretation of PFT data for CCS monitoring. These results are preliminary and do not take into account more realistic vadose zone conditions such as the presence of water, in which PFTs are insoluble. Increased moisture content will likely decrease sorption onto porous media and retardation in the vadose zone may be less than determined in these experiments.

Return to top | Return to Index


MULTIPLE SUPPRESSION IN THE T-X-P DOMAIN

Shaunak Ghosh, M.S.Geo.Sci

University of Texas at Austin, December 2013

Supervisor: Sergey Fomel

112 pages, 50 references

Multiples in seismic data pose serious problems to seismic interpreters for both AVO studies and interpretation of stacked sections. Several methods have been practiced with varying degrees of success to suppress multiples in seismic data. One family of velocity filters for demultiple operations using Radon transforms traditionally face challenges when the water column is shallow. Additionally, the hyperbolic Radon Transform can be computationally expensive. In this thesis, I introduce a novel multiple suppression technique in the t-x-p domain, where p is the local slope of seismic events, which aims at tackling some of the aforementioned limitations, and discuss the advantages and scope of this approach. The technique involves essentially two steps: the decomposition part and the suppression part. Common Mid-Point (CMP) gathers are taken and transformed from the original t-x space to the extended t-x-p space and eventually to the t0-x-p space, where t0 is the zero offset travel time. Multiplication of the gather in the extended space with Gaussian tapering filters, formed using the difference of the powers of the picked primary velocities and intrinsically calculated velocities in terms of t0, x and p using analytical relations, and stacking along the p axis produces gathers with multiples suppressed.

Return to top | Return to Index


ENGINEERING AND ECONOMICS OF ENHANCED OIL RECOVERY IN THE CANADIAN OIL SANDS

Stephen Albert Hester III, MSEER

University of Texas at Austin, May 2014

Supervisor: William L. Fisher

80 pages, 85 references

Canada and Venezuela contain massive unconventional oil deposits accounting for over two thirds of newly discovered proven oil reserves since 2002. Canada, primarily in northern Alberta province, has between 1.75 and 1.84 trillion barrels of hydrocarbon resources that as of 2013 are obtained approximately equally through surface extraction or enhanced oil recovery (EOR) (World Energy Council, 2010). Due to their depth and viscosity, thermal based EOR will increasingly be responsible for producing the vast quantities of bitumen residing in Canada’s Athabasca, Cold Lake, and Peace River formations. Although the internationally accepted 174-180 billion barrels recoverable ranks Canada third globally in oil reserves, it represents only a 9-10% average recovery factor of its very high viscosity deposits (World Energy Council, 2010).

As thermal techniques are refined and improved, in conjunction with methods under development and integrating elements of existing but currently separate processes, engineers and geoscientists aim to improve recovery rates and add tens of billions of barrels of oil to Canada’s reserves (Cenovus Energy, 2013). The Government of Canada estimates 315 billion barrels recoverable with the right combination of technological improvements and sustained high oil prices (Government of Canada, 2013). Much uncertainty and skepticism surrounds how this 75% increase is to be accomplished. This document entails a thorough analysis of standard and advanced EOR techniques and their potential incremental impact in Canada’s bitumen deposits. Due to the extraordinary volume of hydrocarbon resources in Canada, a small percentage growth in ultimate recovery satisfies years of increased petroleum demand from the developing world, affects the geopolitics within North America and between it and the rest of the world, and provides material benefits to project economics.

This paper details the enhanced oil recovery methods used in the oil sands deposits while exploring new developments and their potential technical and economic effect. CMG Stars reservoir simulation is leveraged to test both the feasible recoveries of and validate the physics behind select advanced techniques. These technological and operational improvements are aggregated and an assessment produced on Canada’s total recoverable petroleum reserves. Canada has, by far, the largest bitumen recovery operation in the world (World Energy Council, 2010). Due to its resource base and political environment, the nation is likely to continue as the focus point for new developments in thermal EOR. Reservoir characteristics and project analysis are thus framed using Canada and its reserves.

Return to top | Return to Index


EFFECT OF MODELED PRE-INDUSTRIAL GREENLAND ICE SHEET SURFACE MASS BALANCE BIAS ON UNCERTAINTY IN SEA LEVEL RISE PROJECTIONS IN 2100

Gail Ruth Gutowski, M. S. Geo. Sci.

University of Texas at Austin, August 2013

Supervisors: Donald Blankenship and Charles Jackson

48 pages, 27 references, 2 tables

Changes to ice sheet surface mass balance (SMB) are going to play a significant role in future sea level rise (SLR), particularly for the Greenland ice sheet. The Coupled Model Intercomparison Project Phase 5 (CMIP5) found that Greenland ice sheet (GIS) response to changes in SMB is expected to contribute 9 ± 4 cm to sea level by 2100 (Fettweis et al 2013), though other estimates suggest the possibility of an even larger response.

Modern ice sheet geometry and surface velocities are common metrics for determining a model’s predictability of future climate. However, care must be taken to robustly quantify prediction uncertainty because errors in boundary conditions such as SMB can be compensated by (and therefore practically inseparable from) errors in other aspects of the model, complicating calculations of total uncertainty.

We find that SMB calculated using the Community Earth System Model (CESM) differs from established standards due to errors in the CESM SMB boundary condition. During the long ice sheet initialization process, small SMB errors such as these have an opportunity to amplify into larger uncertainties in GIS sensitivity to climate change. These uncertainties manifest themselves in ice sheet surface geometry changes, ice mass loss, and subsequent SLR.

While any bias in SMB is not desirable, it is not yet clear how sensitive SLR projections are to boundary condition forcing errors. We explore several levels of SMB forcing bias in order to analyze their influence on future SLR. We evaluate ensembles of ice sheets forced by 4 different levels of SMB forcing error, covering a range of errors similar to SMB biases between CESM and RACMO SMB.

We find that GIS SMB biases on the order of 1 m/yr result in 7.8 ± 3.4 cm SLR between 1850 and 2100, corresponding to 100% uncertainty at the 2σ level. However, we find unexpected feedbacks between SMB and surface geometry in the northern GIS. We propose that the use of elevation classes may be incorrectly altering the feedback mechanisms in that part of the ice sheet.

Return to top | Return to Index


HIGH-RESOLUTION CORRELATION FRAMEWORK OF THE GRAYBURG FORMATION-SHATTUCK ESCARPMENT AND PLOWMAN RIDGE : TESTING MODELS OF SHELF-TO-BASIN FRAMEWORKS

Samuel Franz Hiebert, M.S.GeoSci

University of Texas at Austin, August 2013

Supervisor: Charles Kerans

111 pages, 58 references, 1 table

The San Andres and Grayburg Formations are important stratigraphic units for constructing correlation frameworks of the Guadalupe Mountains because these strata record the transition between the ramp profiles of the San Andres along the Algerita Escarpment and the reef-rimmed platforms of the Capitan Formation of the southern Guadalupe Mountains (Franseen et al. 1989). Sarg et al. (1999) and Kerans and Tinker (1999) have published significantly different models of shelf-to-basin correlations within this stratigraphic interval. Central to the debate is the correlation of mixed carbonate-siliciclastic strata exposed at Plowman Ridge in the Brokeoff Mountains to the better-constrained strata along the Shattuck Escarpment in the Guadalupe Mountains. This study applies high-resolution cyclostratigraphy, inorganic carbon isotope geochemistry, and sequence stratigraphic concepts to test the hypothesis that the strata exposed at Plowman Ridge are equivalent to Grayburg strata exposed at the Shattuck Escarpment in the southern Guadalupe Mountains (Kerans and Nance 1991, Kerans and Kempter 2002).

The shelf-to-basin cyclostratigraphic framework of the Grayburg Formation used in this study was established at the Shattuck Escarpment with data compiled from nine detailed measured sections, high-resolution photopans, and petrographic analysis. Based on one- and two-dimensional cycle stacking analysis, the Grayburg Formation was divided into three high-frequency sequences (HFSs). The high-frequency sequences contain transgressive systems tracts separated by maximum flooding surfaces from the highstand systems tracts. The Grayburg high-frequency sequences are composed of between 6 and 20 high-frequency cycles (HFCs), which were identified and classified into vertical facies successions.

The Grayburg succession at Shattuck section 7 (32.09°, -104.81°) was selected as the reference section from the Guadalupe Mountains for comparison with Plowman section PR1 (32.03°, -104.89°) in the Brokeoff Mountains. Correlation between sections is documented at the 3rd-order composite sequence, high-frequency sequence, and when feasible, high-frequency cycle scale. Three high-frequency sequences recognized at Plowman Ridge section PR1 are equivalent to the G10, G11, and G12 Grayburg sequences described at Shattuck section 7. Correlation of the Grayburg G10-G12 high-frequency sequences with the three sequences at Plowman Ridge is based on comparison of overall thicknesses, facies proportions, cycle number, vertical facies succession, stratigraphic position of diagnostic units, and excursions within the inorganic carbon isotope profiles taken from both sections. Establishing the links between Grayburg strata on the Shattuck wall with strata on Plowman Ridge corroborates the framework/correlation scheme of Kerans and Tinker (1999) in lieu of other published correlation frameworks.

Return to top | Return to Index


GEOCHEMICAL EFFECTS OF ELEVATED METHANE IN NEAR-SURFACE SEDIMENTS ABOVE AN EOR/CCUS SITE

Mary Catherine Hingst, M.S.Geo.Sci.

University of Texas at Austin, May 2013

Supervisors: Michael Young and Katherine Romanak

112 pages, 82 references, 9 tables

Carbon capture, utilization and storage (CCUS) aims to reduce CO2 emissions by capturing CO2 from sources and injecting it into geologic reservoirs for enhanced hydrocarbon recovery and storage. One concern is that unintentional CO2 and reservoir gas release to the surface may occur through seepage pathways such as fractures and/or improperly plugged wells.

We hypothesize that CO2 and CH4 migration into the vadose zone and subsequent O2 dilution and Eh and pH changes could create an increased potential for metal mobilization, which could potentially contaminate ground and surface waters. This potential has not been addressed elsewhere. Goals of this study are to understand how the potential for metal mobilization through soil pore water may increase due to CO2 and CH4 and to assess potential impact to aquifers and/or the biosphere. The study was conducted at a CCUS site in Cranfield, MS, where localized seepage of CH4 (45%) from depth reaches the surface and oxidizes to CO2 (34%) in the vadose zone near a plugged well. Four sediment cores (4.5-9m long) were collected in a transect extending from a background site through the area of anomalously high soil gas CO2 and CH4 concentrations. Sediment samples were analyzed for Eh and pH using slurries (1:1 vol. with DI water) in the field and for occluded gas concentrations, metal (Ba, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) concentrations, moisture content, organic carbon content, and grain size in the laboratory. Data from the background reference area (no gas anomaly: occluded gas ~21% O2, ‹1% CO2, 0% CH4) showed oxidized conditions (Eh from 464-508mV) and neutral pH (7.0-7.8) whereas samples collected near the gas anomaly (13-21% O2, 0.1-5% CO2, ‹0.1% CH4) were more reducing (Eh 133-566mV) and more acidic (pH = 5.3-8.0). Significant correlations were found between Eh and O2 (r = 0.95), pH and CO2 (r = -0.88), and between these parameters and acid-leachable metals in samples from within the soil gas anomaly. Correlations quickly weaken away from the anomaly. Statistically, total metal concentrations, except for Ba, are similar in all cores. Acid-mobile metal concentrations, above 5m, increase toward the gas anomaly. The percent of water-mobile metals is very low (‹2%) for all metals in all cores, indicating freely-mobile metals are not affected by elevated CO2/CH4. Conclusions are: 1) oxidation of CH4 to CO2 depletes O2 causing reducing conditions; 2) high CO2 and low O2 affect Eh and pH of sediments which in turn alters mineralogy and bond strength between sediments and adsorbed ions; 3) intrusion of strongly acidic fluids (pH of acid used was 0.39) into these sediments could potentially remove weakly bonded metals or dissolve minerals. Implications from this study are that Eh needs to be considered along with pH when analyzing contamination potential, and that exposure of sediments to reducing, followed by acidic conditions, increases the potential for metal mobilization in the vadose zone. More research is needed to determine the concentration of gases (CO2, CH4 and O2) that will create Eh and pH levels that could affect the mineralogy and sorption mechanism potentially leading to metal mobilization. Methods for assessing potential metal mobilization may be useful for site characterization and risk assessment.

Return to top | Return to Index


TRANSPORT PATHWAYS OF FIRE GENERATED TRACERS TO THE UPPER TROPOSPHERE AS DETERMINED BY A-TRAIN SATELLITE MEASUREMENTS

Lei Huang, Ph.D.

University of Texas at Austin, May 2013

Supervisor: Rong Fu

164 pages, 170 references, 8 tables

Convective and long-range transport of air mass controls the global distributions and impacts of the pollutants generated in limited source regions. However, an observational characterization of such transport based on long-term satellite data has been difficult in part because adequate satellite measurements were not available until recent years and lack of an automated method for identifying the transport pathways. My dissertation addresses this problem through three steps: First, I developed a method to automate the identification of two pathways that are responsible for the transport of biomass burning generated tracers from the surface to the upper troposphere (UT). I focused on carbon monoxide (CO) because it has a relatively long lifetime in the atmosphere, and thus it is commonly used as a tracer of convective and long-range mass transport. Next, I applied this method to investigate the relative importance of the two pathways in determining the seasonal pattern of UT CO distribution. Results show that the seasonality of CO concentrations in the tropical UT mainly reflects the seasonality of the “local convection” pathway, because the “local convection” pathway typically transports significantly more CO to the UT than the “advection within the lower troposphere followed by convective transport” pathway. Then, I investigated the impacts of transport pathways on the interannual variation of tropical UT CO concentration. Results show that the interannual variation of CO in the tropical UT is dominated by UT CO anomaly over Southeast Asia related to the El Niño-Southern Oscillation, and the average mass of CO transported per event of “local convection” is the factor that accounts for the UT CO difference between two El Niño periods.

After that, I began to address the transport of more complex pollutants such as aerosols. First, the seasonal and diurnal variations of the vertical distributions of aerosol properties were characterized through a statistical analysis of aerosol profile data. Then, the transport pathways associated with the aerosol layer at the tropopause level over Asian area during boreal summer were investigated through back-trajectory model analyses. Three major pathways were found and the occurrence frequency of each pathway was analyzed and discussed.

Return to top | Return to Index


BARRIER ISLAND ASSOCIATED WASHOVER FAN AND FLOOD TIDAL DELTA SYSTEMS : A GEOMORPHOLOGIC ANALYSIS AND PROPOSED CLASSIFICATION SCHEME FOR MODERN WASHOVER FANS AND EXAMINATION OF A FLOOD TIDAL DELTA COMPLEX IN THE CRETACEOUS UPPER MCMURRAY FORMATION, ALBERTA, CANADA

Jessica Wager Hudock, M.S. Geo. Sci.

University of Texas at Austin, December 2013

Supervisors: Lesli J. Wood and Peter P. Flaig

118 pages, 77 references, 5 tables

A detailed study of modern washover fan (fan) morphologies will clarify common fan geometries, lead to a better model for a “typical” fan, identify the preservation potential and probable geometries of fan facies in subsurface datasets and outcrops, and ultimately improve hydrocarbon recovery in barrier island reservoir systems. This study uses satellite imagery to conduct a spatial analysis of 118 modern fans to quantify geomorphologic attributes of fans. A new classification scheme for fans is proposed that refines the current fan model, dividing fans into channelized and non-channelized fans. Channelized fans are subdivided according to the location of primary deposition: barrier depo-center or lagoonal depo-center. Non-channelized fans are subdivided based on morphology: dissipative, lobate, or apron-sourced. Quantitative cross-plots of morphologic relationships are analyzed to define trends in fan morphologies. The most common type of fan encountered in our study is a non-channelized, line-sourced, lobate washover fan with an area of less than 1 km2 that is fully contained on a barrier and exhibits no subaqueous deposition in back-barrier waters.

The Lower Cretaceous McMurray Formation is the primary reservoir of the Athabasca Oil Sands in Alberta, Canada. The upper McMurray is commonly interpreted as deposits of embayed coastal systems. Our location is in an under-studied area located 80 km northwest of Fort McMurray. Lateral and vertical facies changes, sedimentary structures, key surfaces, trace fossils, and bitumen saturation were documented in eight cores located along a 20 km transect situated paleo-landward of a Devonian paleo-high acting as a bedrock-barrier. Our data indicate that a flood tidal delta complex prograded landward into a back-barrier embayment through the stable, bedrock-controlled inlet. This system overlies middle McMurray fluvial sands and Devonian basement and was transgressed by marine waters prior to deposition of the overlying Wabiskaw Formation. Flood tidal delta sandbodies are bitumen saturated and therefore make good reservoirs; however, heavily bioturbated tidal flats can act as a barrier to flow where they encase flood tidal deltas, as encased sands were devoid of bitumen. This complex coastal paleogeography produced back-barrier deposits that contain a slightly more diverse, marine trace fossil assemblage than might otherwise be expected.

Return to top | Return to Index


TIME DEPENDENT LEAKAGE OF CO2 SATURATED WATER ALONG A CEMENT FRACTURE

Nicolas John Huerta, Ph.D.

University of Texas at Austin, December 2013

Supervisors: Marc A. Hesse and Steven L. Bryant

279 pages, 79 references, 24 tables

Leakage of CO2 saturated fluid along wellbores has critical implications for the feasibility of geologic CO2 storage. Wells, which are ubiquitous in locations ideal for CO2 storage, develop leaks (e.g. fractures) for many reasons and at different points in their age. Small leaks pose the most significant risk to geological CO2 sequestration because they are difficult to detect and provide a direct pathway through which fluid can escape the storage formation. This dissertation shows that due to complex coupling between reaction and flow, leaking wells will tend to self-seal via secondary precipitation of calcium carbonate in the open pathway. Residence time, fluid reactivity, and initial fracture aperture all play a key role in determining the time required to seal the leakage pathway.

To test the self-sealing hypothesis, laboratory experiments were conducted to inject reactive fluids into naturally fractured cement. Restriction of the leakage pathway, i.e., the fracture, was inferred from the relationship between flow rate and pressure differential. Precipitation was observed in both constant flow rate and constant pressure differential experiments. In the former precipitation resulted in an increasing pressure differential, while precipitation caused a decrease in flow rate in the latter. Analysis by electron microprobe and x-ray diffraction, and corroborated with effluent chemical analysis, showed that the reacted channel was depleted in calcium and enriched in silicon relative to the original material. The remaining silicon rich material prevents widening of the reacted channel and development a self-enhancing (e.g. wormhole) behavior. Self-limiting behavior is caused by calcium mixing with carbonate ions in high pH slow flow regions where local residence time is large and calcium carbonate is insoluble. Secondary precipitation initially develops next to the reacted channel and then across the fracture surface and is the source of pathway restriction and the self-sealing behavior.

Results from the experiments are used to develop a simple analytical model to forecast well scale leakage. Future work is needed to test a broader range of experimental conditions (e.g. brine salinity, cement formulations, cement-earth interface, effect of CO2 saturation, pressure, and temperature), to improve our understanding of both the fundamental behavior and the leakage model.

Return to top | Return to Index


SEISMIC RESERVOIR CHARACTERIZATION OF THE HAYNESVILLE SHALE : ROCK-PHYSICS MODELING, PRESTACK SEISMIC INVERSION AND GRID SEARCHING

Meijuan Jiang, Ph.D.

University of Texas at Austin, Month Year

Supervisor: May 2014

172 pages, 96 references, 5 tables

This dissertation focuses on interpreting the spatial variations of seismic amplitude data as a function of rock properties for the Haynesville Shale. To achieve this goal, I investigate the relationships between the rock properties and elastic properties, and calibrate rock-physics models by constraining both P- and S-wave velocities from well log data. I build a workflow to estimate the rock properties along with uncertainties from the P- and S-wave information. I correlate the estimated rock properties with the seismic amplitude data quantitatively.

The rock properties, such as porosity, pore shape and composition, provide very useful information in determining locations with relatively high porosities and large fractions of brittle components favorable for hydraulic fracturing. Here the brittle components will have the fractures remain opened for longer time than the other components. Porosity helps to determine gas capacity and the estimated ultimate recovery (EUR); composition contributes to understand the brittle/ductile strength of shales, and pore shape provides additional information to determine the brittle/ductile strength of the shale. I use effective medium models to constrain P- and S-wave information. The rock-physics model includes an isotropic and an anisotropic effective medium model. The isotropic effective medium model provides a porous rock matrix with multiple mineral phases and pores with different aspect ratios. The anisotropic effective medium model provides frequency- and pore-pressure-dependent anisotropy.

I estimate the rock properties with uncertainties using grid searching, conditioned by the calibrated rock-physics models. At well locations, I use the sonic log as input in the rock-physics models. At areas away from the well locations, I use the prestack seismic inverted P- and S-impedances as input in the rock-physics models. The estimated rock properties are correlated with the seismic amplitude data and help to interpret the spatial variations observed from seismic data. I check the accuracy of the estimated rock properties by comparing the elastic properties from seismic inversion and the ones derived from estimated rock properties. Furthermore, I link the estimated rock properties to the microstructure images and interpret the modeling results using observations from microstructure images.

The characterization contributes to understand what causes the seismic amplitude variations for the Haynesville Shale. The same seismic reservoir characterization procedure could be applied to other unconventional gas shales.

Return to top | Return to Index


AN ENERGY RETURN ON INVESTMENT FOR A GEOTHERMAL POWER PLANT ON THE TEXAS GULF COAST

Kyle Kampa, M.A.

University of Texas at Austin, May 2013

Supervisor: Carey King

56 pages, 72 references, 12 tables

This thesis examines the energy return on investment (EROI) of a model 3 MW hybrid gas-geothermal plant on the Texas Gulf Coast. The model plant uses a design similar to the DOE Pleasant Bayou No. 2 test geothermal plant, and uses a gas engine to harness entrained methane and an Organic Rankine Cycle turbine to harness thermal energy from hot brines. The indirect energy cost was calculated using the Carnegie Mellon University Economic Input-Output Life Environmental Life Cycle Analysis (EIO-LCA) model. The EROI of the plant using the 1997 EIO-LCA energy data is 12.40, and the EROI of the plant using 2002 EIO-LCA energy data is 14.18. Sensitivity analysis was run to determine how the plant parameters affect the EROI. A literature review of the EROI of different power sources shows that the EROI of the hybrid geothermal plant is greater than the EROI of flash steam geothermal and solar, but is lower than the EROI of dry steam geothermal, wind power, nuclear, coal, gas, and hydroelectric plants. An analysis of the EROI to financial return on investment (FROI) shows that the FROI for a hybrid geothermal plant could be competitive with wind and solar as a viable renewable resource in the Texas electricity market.

Return to top | Return to Index


UNDERSTANDING THE EFFECTS OF WILDFIRE ON SOIL MOISTURE DYNAMICS

Michael Richard Kanarek, M.S.Geo.Sci

University of Texas at Austin, August 2013

Supervisor: M. Bayani Cardenas

57 pages, 43 references, 4 tables

Moisture dynamics in the critical zone have significant implications for a variety of hydrologic processes, from water availability to plants, to infiltration and groundwater recharge rates. These processes are perturbed by events such as wildfires, which may have long-lasting impacts. In September 2011, the most destructive wildfire in Texas history occurred in and around Bastrop State Park, which was significantly affected; thus this is a rare opportunity to study soil moisture under such burned conditions. A 165 m long transect, bridging burned and unburned areas, was established within the “Lost Pines” of the park. Soil moisture was monitored using a variety of methods, including 2D electrical resistivity imaging (using dipole-dipole and Schlumberger configurations), handheld measurements using a ThetaProbe, and readings at depth using PR2 profile probes. Field measurements were collected at approximately one-month intervals to study temporal and seasonal effects on soil moisture. Greater soil moisture was found near the ground surface at the heavily burned end of the transect, where the majority of trees were killed by the fire and grasses now dominate, and lower near-surface soil moisture and higher resistivity at the opposite end of the transect, which is still populated by pine trees. These variations can likely be attributed to the vegetative variations between the two ends of the transect, with trees consuming more water at one end and the ground cover of grasses and mosses consuming less water and helping reduce evaporation at the burned end. Soil texture differences could also be a factor in greater soil moisture retention at the burned end of the transect. Given the higher moisture throughout the soil profile at the burned end of the transect, this could be an indication of greater infiltration, and could increase recharge, at least in the short term.

Return to top | Return to Index


THE 2500 B.P. SAVANNA EXPANSION OF WEST CENTRAL AFRICA: HUMANS OR CLIMATE? : UNDERSTANDING THE RELATIONSHIP BETWEEN THE IRON-AGE BANTU MIGRATION, CLIMATE CHANGE, AND ABRUPT VEGETATION DISTURBANCE IN THE AFRICAN TROPICAL FOREST ZONE DURING THE LATE HOLOCENE FROM LAKE OSSA, CAMEROON

Han Kyul Kim, Bachelor of Science

University of Texas at Austin, May 2013

Supervisor: Timothy Shanahan

30 pages, 38 references

Lake Ossa, in western Cameroon, Africa (3°50' N, 9°36' E) records a sudden rainforest disruption around 2500 cal yr BP, as evident by pollen, sediment, and diatom changes recorded in a sediment core taken in the lake. The observed changes in biological and sedimentary properties have been used to support the notion that an abrupt climate change was responsible for this disruption event. However, the problem becomes more complex as humans are introduced into the picture. It has been found through archeological research that the Bantu, an iron-age people, migrated through the Lake Ossa region around the same period, deforesting large amounts of wood to smelt iron. To correctly discern the role of climate in this event, a climate proxy independent of surface processes must be introduced. In this project, average chain lengths of long n-alkanes from leaf waxes are used to show that the surficial changes far exceeded the impact of climate in the 2500 cal yr BP event.

Return to top | Return to Index


UNDERSTANDING SURFACE WATER - GROUNDWATER INTERACTIONS ON THE BLANCO

Tiffany Noel Kocis, B.S. Hydro geology with Special Departmental Honors

University of Texas at Austin, May 2014

Supervisor: John M. Sharp, Jr.

74 pages, 47 references, 12 tables

The Edwards and Trinity Aquifers supply over 700 million gallons per day (2.6 x 109 I/day) to the public; therefore, it is crucial to understand how water is lost from the Trinity and exchanged into the Edwards. This thesis addresses the following questions in the scope of Hays County, TX: How are gains and losses temporally and spatially distributed along the Blanco River? What controls the distribution of spring discharge contributing to gains along the Blanco River? Finally, what does this spatial and temporal distribution of gains, losses, and joints mean for available water resources? From a time-series analysis of gain-loss on the Blanco River, it is evident that coarse resolution gain-loss studies are not accurate enough to capture the flow dynamics of the river or to understand flow paths along the river, particularly after storm events. The coarse resolution studies miss out on spring discharge zones and on smaller, but significant recharge zones located within net-gain reaches. The detailed gain-loss study from November 2013 was compared to a detailed study conducted in January 1955; the comparison suggests that that gain-loss conditions change depending on flow conditions and that regions that serve as aquifer recharge zones during low flow conditions serve as discharge zones during high flow conditions, which may serve to offset water level declines in the aquifer at the beginning of a drought because recharge into the aquifer is sustained by flow in the Blanco River. Furthermore, when comparing the present method for estimating recharge (estimated as loss between two USGS gauges), using only the loss estimated by the gauges instead of a detailed gain-loss study is a significant underestimate (by 5 times) of the total amount of recharge entering the Edwards-Trinity system along the Blanco River. Finally, the structural analysis of fracture orientations suggests that the spring discharge fracture networks are actually joint networks controlled by both topography and the development of the Balcones Fault Zone. To conclude, both parts of this study have important implications for groundwater resources: understanding gain-loss dynamics provides an important dataset for Groundwater Availability Models and for conservation districts who must allocate water resources, and understanding the joint networks through which springs discharge could allow drillers to target high water yield fractures.

Return to top | Return to Index


CHARACTERIZATION AND PREDICTION OF RESERVOIR QUALITY IN CHLORITE-COATED SANDSTONES: EVIDENCE FROM THE LATE CRETACEOUS LOWER TUSCALOOSA FORMATION AT CRANFIELD FIELD, MISSISSIPPI, U.S.A.

Masoumeh Kordi, Ph.D.

University of Texas at Austin, May 2013

Supervisors: William L. Fisher and Susan D. Hovorka

193 pages, 257 references, 7 tables

The effectiveness of CO2 injection in the subsurface for storage and EOR are controlled by reservoir quality variation. This study determines the depositional processes and diagenetic alterations affecting reservoir quality of the Lower Tuscaloosa Formation at Cranfield Field. It also determines the origin, time and processes of the grain-coating chlorite and its impacts on reservoir quality. Moreover, by integrating depositional and diagenetic characteristics and by linking them to sequence stratigraphy, the distribution of reservoir quality, could be predicted within a sequence stratigraphic framework.

The studied sandstones are composed of medium to coarse-grained, moderately sorted litharenite to sublitharenite with composition of Q76.1F0.4L23.5. Depositional environment of this formation in the Mississippi Interior Salt Basin is interpreted as incised-valley fluvial fill systems. The cross sections and maps at the field show trend of the sandy intervals within channels with a NW-SE paleocurrent direction.

During burial of the sandstones, different digenetic alterations including compaction, dissolution, replacement and cementation by chlorite, quartz, carbonate, kaolinite, titanium oxides, pyrite and iron-oxide modified the porosity and permeability. Among these, formation of chlorite coats plays the most important role in reservoir quality. The well-formed, thick and continuous chlorite coatings in the coarser grain sandstones inhibited formation of quartz overgrowth, resulted in high porosity and permeability after deep burial; whereas the finer grain sandstones with the poorly-formed, thin and discontinuous chlorite coatings have been cemented by quartz. The optimum amount of chlorite to prevent formation of quartz overgrowths is 6% of rock volume.

The chlorite coats are composed of two layers including the inner chlorite layer formed by transformation of the Fe-rich clay precursors (odinite) through mixed-layer clays (serpentine-chlorite) during early eodiagenesis and the outer layer formed by direct precipitation from pore waters through dissolution of ferromagnesian rock fragments during late eodiagenesis to early mesodiagenesis.

In the context of the reservoir quality prediction within sequence stratigraphic framework, the late LST and early TST are suitable for deposition of chlorite precursor clays, which by progressive burial during diagenesis could be transformed to chlorite, and thus results in preserving original porosity and permeability in deep burial.

Return to top | Return to Index


TRACKING THE TRANSITION FROM AERIAL TO AQUATIC FLIGHT IN BIRDS USING QUILL MARKINGS

Nicole Kurka, B.S. in General Geology

University of Texas at Austin, May 2014

Supervisor: Julia Clarke

56 pages, 33 references, 1 table

Quill markings, also known as papillae remigalis, are created by the attachment of the secondary feathers to the ulna. In most birds, quill markings manifest as tubercles formed by ligamentous attachments. However, in wing-propelled diving taxa, depressions are often present, and the functional significance of these has not been well studied. Here quill marking morphology was assessed in Charadriiformes (shorebirds) and a large waterbird clade. Both clades include taxa such as penguins and auks that use their wings in underwater propulsion. The identity of tubercles and depressions as well as their relationship with the position and morphology of secondary and covert feathers is documented for the first time. Assessment of quill marking data for penguins, ale ids, and outgroups in a phylogenetic context also reveals changes in quill markings related to locomotor mode. Dissections, examination of skeletons and fossils, and CT scans were utilized to assess quill marking morphology. The results indicate that the transition from aerial to aquatic flight (i.e., origin of wing propelled diving) involves a transition from widely spaced tubercles, to closely spaced dorsal tubercles, to depressions, accompanied by the movement of ligamentous attachments to the dorsal surface of the ulna and eventual loss or reduction of ligamentous attachments. It also involves a transition from faint depressions produced by secondary feathers to deep depressions created by covert feathers. The numerous similarities between quill markings of distantly related species with the same locomotor ecology are a strong argument for changes in locomotor mode affecting changes in quill markings. Feather taxis and ontogeny are shown to influence the morphology of quill markings as well. The impacts of this study go beyond aquatic birds. Fossilized feathers are rarely preserved, so quill markings are often all that is left to infer information about feather and wing morphology. Quill markings may be used as a key tool not only to study changes in the wing associated with the origin of aquatic flight, but also in the evolution of avian flight.

Return to top | Return to Index


GEOCHEMICAL AND THERMAL INSIGHTS INTO CALDERA-FORMING “SUPER-ERUPTIONS”

Ethan T. Lake, Ph.D.

University of Texas at Austin, May 2013

Supervisor: Mark Cloos

325 pages, 190 references, 8 tables

Explosive, caldera forming “super-eruptions” (an eruption of VEI 8 or larger, resulting in 1000+ km3 of volcanic ejecta in ignimbrite sheets) are the single most destructive natural disaster native to Earth. Super-eruptions require three elements to occur: 1-crustal magmatic fluxes above background solidification rates, 2-growth of a batholith scale magma chamber, and 3-an eruption trigger. This study addresses these requirements with new petrographic and geochemical analyses and numerical simulations of crustal magma bodies.

Crustal magmatic fluxes up to 10x steady-state arc rates are required to form volcanic provinces that host super-eruptions. Super-eruptions can occur in continental hot-spots or rift environments. Why arcs “flare-up” is the subject of active debate. Arcs may follow a regular cycle of lithospheric thickening, delamination, and asthenospheric upwelling (the Andean cycle); alternatively fertilized lithospheric mantle may undergo rapid melting. Targeted sampling (n = 165) of mapped but unsampled mafic and lamprophyric magmas in the San Juan magmatic locus of Colorado, an archetypical ignimbrite province, over three years identified both the lithospheric mantle reservoir and the most primitive San Juan magmas using optical petrography, whole rock geochemistry (n = 50) and Pb, Sr, and Nd isotope geochemistry (n = 32). These mafic magmas more closely resemble the continental lithosphere geochemically. Mixing models based on Energy Constrained Assimilation/Fractional-Crystallization (EC-AFC) indicate that the San Juan magmatism is the product of lithospheric melts and 30-40% crustal assimilation rather than asthenospheric upwelling. The Farallon flat-slab “pre-fluxed” and refrigerated the Colorado lithospheric mantle; removal of that slab at around 40 Ma triggered the SJVF “flare-up.”

Numerical simulations of crustal magma chamber growth indicate giant magma chambers form when high magma fluxes raise upper crustal temperatures to 300-400 °C at 5-10 km depth. These simulations focus on chamber growth, convection, and cooling at the expense of geometry or chamber mechanical failure with realistic sill-like geometry at the expense of thermal modeling. New 3D finite difference simulations emphasize the importance of geometry on chamber lifespan and crustal heating. A spherical chamber (i.e. model construct) requires 10x the cooling time of a 2km caldera footprint sill of same volume. Increasing sill thickness by 1km can double chamber longevity. Focused intrusions (i.e. 1D modeling) locally produce higher thermal gradients and preserve larger primary basalt volumes. Random intrusions in 3D yield basalt to crust ratios of 3-4:1 (required in the EC-AFC models). Random intrusion in 3D into the upper crust at “flare-up” fluxes (=10 km3 per k.y.) elevate average crustal geotherms by 10 °C / km, allowing for growth of batholithic scale magma chambers a wider footprint.

Once situated in the upper crust, sub-caldera magma chambers cool inward forming moving crystallization and fluid saturation fronts. If the saturation front propagates faster than the crystallization front, nucleating fluid bubbles have the opportunity to grow, ascend, and collect at the chamber roof. New 2D finite difference models couple magma chamber cooling to fluid production to explore the conditions of fluid escape and collection. Less silicic magma composition, equant geometry, high ambient thermal gradient, and a stock all aid in fluid pocket growth by slowing the advance of the crystallization front (a fluid trap) and triggering saturation at lower fluid concentrations. Fluid pockets that grow to certain sizes ( > 500 m hemispherical bubble) have the potential to trigger an eruption by propagation of a fluid fracture to the surface. This mechanism possibly triggered the eruption of the 5000+ km3 Fish Canyon Tuff as well as smaller, recent eruptions (Pinatubo, El Chichón).

Caldera forming super-eruptions occur in regions that meet these three requirements: 1-high magmatic flux, 2-rapid growth to batholithic size, and 3-a delayed eruption trigger. For the SJVF of Colorado melting of the “pre-fluxed” lithosphere provided the magmatic pulse which melted and heated the crust, forming a broad batholith. As magmatism peaked and began to wane, upper crustal magma chambers started to crystallize, exsolving fluids. These fluids ascended, collected, and fractured their way to the surface, triggering the Fish Canyon Tuff and other eruptions.

Return to top | Return to Index


OPTICAL REMOTE SENSING OF GLACIERS IN THE NORTHERN HIMACHAL PRADESH

Daniel N. Le, Bachelor of Science

University of Texas at Austin, May 2014

Supervisor: Ginny A. Catania

34 pages, 23 references, 2 tables

Glaciers in the Himalaya are characterized by high regional variability in response to climate. Some of these glaciers can be important water resources for municipal and agricultural use downstream, mainly in the arid areas of the northwestern Himalaya. The harsh terrain, large number of glaciers (more than 40,000 glaciers in high mountain Asia), lack of long-term field observations and poor infrastructure in the surrounding nations make it difficult to conduct detailed glacier mass balance studies in the Himalaya. Remote sensing not only offers an alternative to field-based mass balance studies, but also offers highly efficient methods for characterizing large numbers of glaciers. This study offers an optical remote sensing based algorithm to identify snow cover area using a threshold reflectance value, which can be associated with the accumulation area of a glacier. Using the accumulation area, the area-accumulation ratio (AAR) can be produced and used as a proxy for glacier health. By comparing glacier health to other glacier attributes, we find that though this specific area in the northern Himachal Pradesh is characterized by high variability, but there are still relationships that can be developed between different glacier characteristics (glacier area, mean aspect, minimum elevation, etc.).

Return to top | Return to Index


FROM RIFTING TO COLLISION : THE EVOLUTION OF THE TAIWAN MOUNTAIN BELT

Ryan Lester, PhD

University of Texas at Austin, May 2013

Supervisors: Kirk D. McIntosh and Luc L. Lavier

222 pages, 208 references, 3 tables

Arc-continent collisions are believed to be an important mechanism for the growth of continents. Taiwan is one of the modern day examples of this process, and as such, it is an ideal natural laboratories to investigate the uncertain behavior of continental crust during collision. The obliquity of collision between the northern South China Sea (SCS) rifted margin and Luzon arc in the Manila trench subduction zone allows for glimpses into different temporal stages of collision at different spatial locations, from the mature mountain-belt in central-northern Taiwan to the ‘pre-collision’ rifted margin and subduction zone south of Taiwan. Recently acquired seismic reflection and wide-angle seismic refraction data document the crustal-scale structure of the mountain belt through these different stages.

These data reveal a wide rifted margin near Taiwan with half-graben rift basins along the continental shelf and a broad distal margin consisting of highly-extended continental crust modified by post-rift magmatism. Magmatic features in the distal margin include sills in the post-rift sediments, intruded crust, and a high-velocity lower crustal layer that likely represents mafic magmatism. Post-rift magmatism may have been induced by thermal erosion of lithospheric mantle following break-up and the onset of seafloor spreading.

Geophysical profiles across the early-stage collision offshore southern Taiwan show evidence the thin crust of the distal margin is subducting at the Manila trench and structurally underplating the growing orogenic wedge ahead of the encroaching continental shelf. Subduction of the distal margin may induce a pre-collision flexural response along the continental shelf as suggested by a recently active major rift fault and a geodynamic model of collision. The weak rift faults may be inverted during the subsequent collision with the continental shelf. These findings support a multi-phase collision model where the early growth of the mountain belt is driven in part by underplating of the accretionary prism by crustal blocks from the distal margin. The wedge is subsequently uplift and deformed during a collision with the continental shelf that involves both thin-skinned and thick-skinned structural styles. This model highlights the importance of rifting styles on mountain-building.

Return to top | Return to Index


CENOZOIC SEDIMENTATION AND EXHUMATION OF THE FORELAND BASIN SYSTEM IN THE PRECORDILLERA FOLD-THRUST BELT (31-32°S), SOUTHERN CENTRAL ANDES, ARGENTINA

Mariya Levina, M.S.Geo.Sci.

University of Texas at Austin, May 2013

Supervisor: Brian K. Horton

100 pages, 54 references, 3 tables

Andean retroarc shortening associated with flattening of the Pampean segment of the subducting Nazca plate has resulted in a thin-skinned, east-directed thrust system that partitioned and uplifted Cenozoic foreland basin fill in the Precordillera of west-central Argentina. The temporal and kinematic evolution of the Precordillera fold-thrust belt can be approached through detailed analyses of the clastic sedimentary deposits now preserved in intermontane regions between major thrust faults. In this project, we focus on the uppermost Oligocene–Miocene basin fill exposed in the axial and eastern Precordillera along the San Juan River (Quebrada Albarracín and Pachaco regions) and western flank of the frontal structure (Sierra Talacasto). The nonmarine successions exposed in these regions record hinterland construction of the Frontal Cordillera, regional arc volcanism, and initial exhumation of the Precordillera thrust sheets.

Measured stratigraphic sections and lithofacies analyses of the preserved stratigraphic successions reveal initial development at ~24 Ma of an eolian depositional system influenced by regional volcanism and fluvial interactions, becoming a fully eolian system by 21-19 Ma. This system transitioned to a distributary fluvial system in which regions closer to the deformation front recorded sandy-gravelly braided stream sedimentation and regions farther east recorded more-distal floodplain-dominated deposition of thin-bedded mudstone and sandstone. The youngest sedimentary record is preserved in the Albarracin basin, a zone strongly influenced by explosive volcanism of nearby eruptive centers around 14 Ma, followed by a progradational alluvial-fan succession of pebbly, cross-stratified sandstone and thick, pebble to cobble conglomerate.

Provenance changes recorded by detrital zircon U-Pb age populations suggest that initial deformation in the Frontal Cordillera coincided with the early Miocene transition from eolian to fluvial deposition in the adjacent foreland basin. The overall upward coarsening nature of the fluvial succession and increased presence of Paleozoic clasts reflect the eastward progression of thin-skinned deformation in the Precordillera and resultant structural partitioning of the synorogenic foreland successions. Using apatite (U-Th)/He thermochronometry we are able to further constrain the age of uplift-induced exhumation and cooling of several Precordillera thrust sheets to 12-9 Ma. This apparent pulse of exhumation is evident in all three sections, suggesting rapid, large-scale exhumation by synchronous thrusting above a single décollement linking major structures of the eastern Precordillera.

Return to top | Return to Index


SEISMIC IMAGING AND VELOCITY MODEL BUILDING WITH THE LINEARIZED EIKONAL EQUATION AND UPWIND FINITE-DIFFERENCES

Siwei Li, Ph.D.

University of Texas at Austin, May 2014

Supervisor: Sergey B. Fomel

180 pages, 157 references

Ray theory plays an important role in seismic imaging and velocity model building. Although rays are the high-frequency asymptotic solutions of the wave equa- tion and therefore do not usually capture all details of the wave physics, they provide a convenient and effective tool for a wide range of geophysical applications. Especially, ray theory gives rise to traveltimes. Even though wave-based methods for imaging and model building had attracted significant attentions in recent years, traveltime- based methods are still indispensable and should be further developed for improved accuracy and efficiency. Moreover, there are possibilities for new ray theoretical methods that might address the difficulties faced by conventional traveltime-based approaches. My thesis consists of mainly four parts. In the first part, starting from the linearized eikonal equation, I derive and implement a set of linear operators by upwind finite-differences. These operators are not only consistent with fast-marching eikonal solver that I use for traveltime computation but also computationally efficient. They are fundamental elements in the numerical implementations of my other works. Next, I investigate feasibility of using the double-square-root eikonal equation for near surface first-break traveltime tomography. Compared with traditional eikonal-based approach, where the gradient in its adjoint-state tomography neglects information along the shot dimension, my method handles all shots together. I show that the double-square-root eikonal equation can be solved efficiently by a causal discretization scheme. The associated adjoint-state tomography is then realized by linearization and upwind finite-differences. My implementation does not need adjoint state as an intermediate parameter for the gradient and therefore the overall cost for one linearization update is relatively inexpensive. Numerical examples demonstrate stable and fast convergence of the proposed method. Then, I develop a strategy for compressing traveltime tables in Kirchhoff depth migration. The method is based on differentiating the eikonal equation in the source position, which can be easily implemented along with the fast-marching method. The resulting eikonal-based traveltime source-derivative relies on solving a version of the linearized eikonal equation, which is carried out by the upwind finite-differences operator. The source-derivative enables an accurate Hermite interpolation. I also show how the method can be straightforwardly integrated in anti-aliasing and Kirchhoff redatuming. Finally, I revisit the classical problem of time-to-depth conversion. In the presence of lateral velocity variations, the conversion requires recovering geometrical spreading of the image rays. I recast the governing ill-posed problem in an optimization framework and solve it iteratively. Several upwind finite-differences linear operators are combined to implement the algorithm. The major advantage of my optimization-based time-to-depth conversion is its numerical stability. Synthetic and field data examples demonstrate practical applicability of the new approach.

Return to top | Return to Index


DIRECT SHEAR WAVE POLARIZATION CORRECTIONS AT MULTIPLE OFFSETS FOR ANISOTROPY ANALYSIS IN MULTIPLE LAYERS

Jacqueline Patrice Maleski, M.S. Geo. Sci

University of Texas at Austin, May 2014

Supervisor: Robert Tatham

91 pages, 45 references, 6 tables

Azimuthal anisotropy, assumed to be associated with vertical, aligned cracks, fractures, and subsurface stress regimes, causes vertically propagating shear waves to split into a fast component, with particle motion polarized parallel to fracture strike, and a slow component, with particle motion polarized perpendicular to fracture strike. Determining the polarization of each split shear wave and the time lag between them provides valuable insight regarding fracture azimuth and intensity. However, analysis of shear wave polarizations in seismic data is hampered by reflection-induced polarization distortion. Traditional polarization analysis methods are limited to zero offset and are not valid if implemented over the full range of offsets available in typical 3D seismic data sets. Recent proposals for normalizing amplitudes recorded at non-normal incidence to values recorded at normal incidence may provide an extension to correcting offset-dependent shear wave polarization distortion. Removing polarization distortion from shear wave reflections allows a larger range of offsets to be used when determining shear wave polarizations. Additional complexities arise, however, if fracture orientation changes with depth. Reflections from layers with different fracture orientations retain significant energy on off-diagonal components after initial rotations are applied. To properly analyze depth-variant azimuthal anisotropy, time lags associated with each interval of constant anisotropy are removed and additional iterative rotations applied to subsequent offset-normalized reflections. Synthetic data is used to evaluate the success of these methods, which depends largely on the accuracy of AVA approximations used in the correction. The polarization correction effectively removes SV polarity reversals but may be limited in corrections to SH polarizations at very far offsets. After the polarization correction is applied, energy calculations including incidence angles up to 20° more effectively compensates individual SV and SH reflection components, allowing for more faithful polarization information identification of the isotropy plane and the symmetry axis. The polarization correction also localizes diagonal component energy maxima and off-diagonal component energy minima closer to the true orientation of the principal axes when a range of incidence angles up to 20° is used.

Return to top | Return to Index


GEOSCIENCE AND DECISION MAKING FOR GEOTHERMAL ENERGY : A CASE STUDY

Reed Ahti Malin, M.A., M.PAff.

University of Texas at Austin, May 2013

Supervisor: Suzanne A Pierce

94 pages, 99 references, 1 table

In September 2009 exploratory testing of an old geothermal power well caused a blowout at the El Tatio geothermal field of northern Chile. El Tatio is the largest geyser field in the southern hemisphere. The blowout was a paradigm-shifting event for the management of the El Tatio geothermal field and drew attention to the disparity and critical nature of scientific information sharing.

This study uses the El Tatio incident as a case study for examining problems of common-pool resource management and geothermal energy development. It explores how differing valuations of geothermal resources resulted in a breakdown of coherent regulation and negative outcomes for all stakeholders. Contingent valuation methods were used to create an elicitive interview process in order to assess how differences in valuation drove these conflicts and negative outcomes. The sharing of scientific information through Decision Support Systems (DSS) is identified as an important element in resolving these conflicts and creating new policies for common-pool resource management.

These methods are presented as tools that can be used by stakeholders to find common ground and seek mutually beneficial outcomes. In addition, these tools can help with the critical issue of social perception of scientific data and science driven solutions to these problems. This study posits that the path forward is to ensure not only that scientific data is communicated in modes appropriate to the community and problem at hand, but that the acquisition and interpretation of this data is informed by stakeholder needs.

Return to top | Return to Index


STRUCTURAL FRAMEWORK AND SEISMIC GEOMORPHOLOGY OF THE CRETACEOUS BENEATH THE MAD DOG AREA, DEEP TO ULTRADEEP WATERS GULF OF MEXICO

Damian Markez, M.S. Geo. Sci.

University of Texas at Austin, May 2013

Supervisor: Lesli J. Wood

69 pages, 105 references

Recent drilling of deep stratigraphy in subsalt offshore Gulf of Mexico has revealed the presence of thick, amalgamated, Cretaceous siliciclastic reservoirs with the potential to become valid exploration targets. Similar to the Lower Tertiary deepwater play, the significant down-dip distance (› 400 km) from the source deltaics, the data gap across the modern structurally complex salt-tectonics-dominated slope and the difficulties of imaging subsalt stratigraphy pose challenges for the construction of meaningful deepwater system models to aid in exploration and appraisal efforts.

A 3D seismic dataset in the Mad Dog field at the basinward end of the modern allochthonous salt canopy and outboard of the Sigsbee Escarpment offers the opportunity to study the nature of the deep stratigraphy at central positions in the basin. The nature of the Cretaceous sedimentary system has been investigated through detailed structural and seismic geomorphologic mapping. An early syndepositional contractional event has been identified and temporally associated with Mesozoic emplacement of a deep salt sheet. These events are masked by the major Neogene-age phase of fold amplification that dominates the present-day subsalt structural framework. Ponded-basin deepwater sedimentation processes control early phases of deposition in the Cretaceous Mad Dog area and sediment-gravity flows are deposited as complexes of low sinuosity amalgamated channelized deposits in roughly-confined sediment pathways. Ponded fills show internal lateral accretion architectures that grow sigmoid in nature as the migrating systems interact with the approaching minibasin margins making evident the structural control on sediment architecture. Later phases of deposition are characterized by slightly sinuous feeder channels with multiple lobe development at their terminus. Variable directions of sediment source pathways indicate a linear-sourced slope apron depositional model for these systems. In addition to the more structured morphologic elements, there were also pervasive mass-transport processes active, presumably triggered by Mesozoic halokinesis. Data in sparse deep wells in the GoM that penetrate the Cretaceous suggest that the Late Cretaceous deepwater depositional system was composed of coarse-grained high density gravity flows. The geometries seen in seismic beneath the Mad Dog area support the existence of such a basinwardly extensive deepwater fan systems developed during the Cretaceous, and the low sinuosity channel geometries and small length:width ratio and amalgamated nature of fan lobes suggest that these systems may have indeed been high-density in nature.

Return to top | Return to Index


THE OSTEOLOGY OF SARAHSAURUS AURIFONTANALIS AND GEOCHEMICAL OBSERVATIONS OF THE DINOSAURS FROM THE TYPE QUARRY OF SARAHSAURUS (KAYENTA FORMATION), COCONINO COUNTY, ARIZONA

Adam Douglas Marsh, M.S. Geo. Sci.

University of Texas at Austin, May 2013

Supervisor: Timothy Rowe

333 pages, 308 references, 11 tables

Sarahsaurus aurifontanalis is the most recent sauropodomorph dinosaur to be discovered and named from the Early Jurassic of North America. The dinosaur is represented by a mostly complete and articulated holotype specimen that preserves a unique manual phalangeal count of 2-3-4-2-2 and accessory pubic foramen adjacent to the obturator foramen. The holotype of Sarahsaurus comprises a braincase and isolated cranial elements, but the skull previously referred to this taxon, MCZ 8893, can only be provisionally referred to Sarahsaurus until additional crania are found associated with postcranial material. Sarahsaurus comes from the middle third of the Kayenta Formation, which is considered to be Early Jurassic in age despite the absence of a radiometric date from that unit. A new technique used to obtain a U-Pb radiometric date from the type quarry of Sarahsaurus in the Kayenta Formation was influenced by secondary uranium enrichment in the open system of the fossil bone. That suggests that uranium within the Kayenta Formation may be the result of the movement of groundwater during the Laramide orogeny in the Late Cretaceous and Early Eocene, and lends support to the hypothesis that the uplift of the Colorado Plateau began relatively early in Late Cretaceous to the Eocene.

Return to top | Return to Index


ENERGY INTENSITY RATIOS AS NET ENERGY MEASURES FOR SELECTED COUNTRIES 1978-2010

John Paul Maxwell, MSEER & MPAff

University of Texas at Austin, December 2013

Supervisor: Supervisor: Carey W. King and Jay W. Zarnikau

124 pages, 73 references, 2 tables

Stated simply, this thesis focuses on the relationship between energy and the economy. Using the foundation of King 2010, this analysis expands the scholarship from a U.S. focus to perform Energy Intensity Ratio analysis on forty-four countries for the time period 1978-2010. There are four fuels examined: coal, natural gas, crude oil and electricity. Using both the price and expenditures based Energy Intensity Ratio methods, outputs for each fuel in any applicable sector was determined. In addition, this work compiles an estimate of the total energy expenditures for the majority of the world. By examining the overall expenditures of gross domestic product spent on energy, the data showed two points in time where energy appears to become a constraint on growth. Though this thesis does not answer the question directly as to whether an increase in energy expenditures “causes” an increase in economic growth, or whether an increase in economic growth “causes” an increase in energy expenditures, the research shows that there may be a “threshold” effect whereby as energy expenditures become a greater share of output, the ability of economic growth to take place is affected.

Return to top | Return to Index


CRYSTALLIZATION OF METAMORPHIC GARNET : NUCLEATION MECHANISMS AND YTTRIUM AND RARE-EARTH-ELEMENT UPTAKE

Stephanie Jean Moore, PhD

University of Texas at Austin, May 2014

Supervisor: William D. Carlson

183 pages, 135 references, 8 tables

This dissertation focuses on two areas of garnet porphyroblast crystallization that have until now remained largely uninvestigated: epitaxial nucleation of garnet porphyroblasts and yttrium and rare earth (Y+REE) uptake in metamorphic garnet.

The mechanism of epitaxial nucleation is explored as a step towards determining which aspects of interfaces are significant to interfacial energies and nucleation rates. Garnet from the aureole of the Vedrette di Ries tonalite, Eastern Alps, shows a clear case of epitaxial nucleation in which garnet nucleated on biotite with (110)grt || (001)bt with [100]grt || [100]bt. The occurrence is remarkable for the clear genetic relationships revealed by the microstructures and for its preservation of the mica substrate, which allows unambiguous determination of the coincident lattice planes and directions involved in the epitaxy. Not all epitaxial nucleation is conspicuous; to increase the ability to document epitaxial relationships between garnet and micas, I develop and apply a method for determining whether evidence for epitaxial nucleation of garnet is present in porphyroblasts containing an included fabric. Although the magnitude of uncertainties in orientation measurements for garnets from Passo del Sole (Switzerland), the Nevado Filabride Complex (Spain), and Harpswell Neck (USA) preclude definitive identification of epitaxial relationships, the method has potential to become a viable technique for creating an inventory of instances and orientations of epitaxial nucleation with appropriate sample selection. Using lattice-dynamics simulations, I explore the most commonly documented epitaxial relationship, (110)grt || (001)ms. The range of interfacial energies resulting from variations in the intracrystalline layer within garnet at the interface, the initial atomic arrangement at the interface, and the rotational orientation of the garnet structure relative to the muscovite structure shows that the intracrystalline layer within garnet has the greatest effect on interfacial energy.

A complete understanding of the role of intergranular diffusion for yttrium and rare-earth-element uptake in porphyroblastic garnet is critical because the complexities of Y+REE zoning in garnets and the mechanisms of Y+REE uptake have implications for petrologic interpretations and garnet-based geochronology. Y+REE distributions in garnets from the Picuris Mountains (USA), Passo del Sole (USA), and the Franciscan Complex (USA) imply diverse origins linked to differing degrees of mobility of these elements through the intergranular medium during garnet growth.

Return to top | Return to Index


SKELETAL ONTOGENY OF MONODELPHIS DOMESTICA (MAMMALIA: DIDELPHIDAE): QUANTIFYING VARIATION, VARIABILITY, AND TECHNIQUE BIAS IN OSSIFICATION SEQUENCE RECONSTRUCTION.

Zachary Stephen Morris, M.S. Geo. Sci.

University of Texas at Austin, December 2013

Supervisor: Timothy Rowe

204 pages, 73 references, 5 tables

The field of evolutionary developmental biology (evo-devo) focuses on understanding the evolution of ontogeny and mechanisms of evolutionary change. Recently, taxonomic comparisons of the sequence of skeletal ossification have become prominent in evo-devo. However, most of these studies fail to consider two major issues: how the technique used to assay ossification and ontogenetic variation and variability may affect comparisons among taxa. This study focuses on the onset of ossification in the skeleton of Monodelphis domestica and quantifies the affects of variation, variability, and technique bias on reconstructions of ontogeny.

Previous comparisons among mammalian taxa have used both computed tomography (CT) and clearing-and-staining (CS) to assess the presence or absence of skeletal elements (i.e., skeletal maturity). In this study, CT and CS were used on the same specimen to compare how these methods assess skeletal maturity. The comparisons of the same individual under reveal significant differences in how skeletal maturity is assessed by CT and CS techniques. Further, significant biases were recovered between techniques. CT is more likely to reveal cranial elements that CS does not, whereas CS is more likely to reveal appendicular elements that CT does not.

To assess levels of variation and variability, Ontogenetic Sequence Analysis (OSA) was used to characterize the ontogeny of Monodelphis domestica. This revealed significant levels of variation with over 800 different ontogenetic pathways recovered for the onset of ossification of all skeletal elements studied. Additionally, high levels of variability were also reconstructed because the majority of specimens were found to exhibit non-modal ontogenetic sequences. This variability is more highly concentrated in the sequence of cranial ossification, suggesting potential modularity in ontogenetic variation and variability. Finally, OSA revealed that technique bias could importantly affect reconstructions of skeletal ossification sequences because no identical sequences were recovered by the CT and CS datasets.

The results of this study demonstrate the importance of considering the primary nature of developmental studies, the specimen. Only by recognizing and quantifying the complexities of evo-devo research, especially natural variation and methodological biases, can more complete understandings of the evolution of ontogeny be had.

Return to top | Return to Index


SEISMIC SENSITIVITY TO VARIATIONS OF ROCK PROPERTIES IN THE PRODUCTIVE ZONE OF THE MARCELLUS SHALE, WV

Sharif Munjur Morshed, M.S. Geo.Sci.

University of Texas at Austin, December 2013

Supervisor: Robert H. Tatham

89 pages, 63 references, 7 tables

The Marcellus Shale is an important resource play prevalent in several states in the eastern United States. The productive zone of the Marcellus Shale has variations in rock properties such as clay content, kerogen content and pore aspect ratio, and these variations may strongly effect elastic anisotropy. The objective of this study is to characterize surface seismic sensitivity for variations in anisotropic parameters relating to kerogen content and aspect ratio of kerogen saturated pores. The recognized sensitivity may aid to characterize these reservoir from surface seismic observations for exploration and production of hydrocarbon.

In this study, I performed VTI anisotropic modeling based on geophysical wireline log data from Harrison County, WV. The wireline log data includes spectral gamma, density, resistivity, neutron porosity, monopole and dipole sonic logs. Borehole log data were analyzed to characterize the Marcellus Shale interval, and quantify petrophysical properties such as clay content, kerogen content and porosity. A rock physics model was employed to build link between petrophysical properties and elastic constants. The rock physics model utilized differential effective medium (DEM) theory, bounds and mixing laws and fluid substitution equations in a model scheme to compute elastic constants for known variations in matrix composition, kerogen content and pore shape distribution.

The seismic simulations were conducted applying a vertical impulse source and three component receivers. The anisotropic effect to angular amplitude variations for PP, PS and SS reflections were found to be dominantly controlled by the Thomsen ε parameter, characterizing seismic velocity variations with propagation direction. These anisotropic effect to PP data can be seen at large offset (›15° incidence angle). The most sensitive portion of PS reflections was observed at mid offset (15°-30°). I also analyzed seismic sensitivity for variations in kerogen content and aspect ratio of structural kerogen. Elastic constants were computed for 5%, 10%, 20% and 30% kerogen content from rock physics model and provided to the seismic model. For both kerogen content and aspect ratio model, PP amplitudes varies significantly at zero to near offset while PS amplitude varied at mid offsets (12 to 30 degree angle of incidences).

Return to top | Return to Index


DYNAMIC STRATIGRAPHY AND SEDIMENT PARTITIONING OF HIGH-SUPPLY FLUVIAL SUCCESSION IN MAASTRICHTIAN SOURCE-TO-SINK SYSTEM

Allison Marie Ned, MS Geo Sci

University of Texas at Austin, May 2013

Supervisors: Ronald J. Steel and Cornel Olariu

88 pages, 53 references, 2 tables

The sediment budget and paleogeography was reconstructed for the Maastrichtian fluvial to coastal plain Lance Formation (›200m thick) that developed coevally with the shoreline/shelf Fox Hills Sandstone (›200m thick) and deep-water Lewis Shale (›750m thick) in a complete source-to-sink system in the Washakie and Great Divide Basins of south central Wyoming. The system initiated during the final Western Interior Seaway (WIS) transgression and the onset of the Laramide Orogeny rapid subsidence (›2km in 1.9 My) that largely outpaced sediment flux into the basin so the system became and remained a deep-water (›500m water depth) basin beyond the Lance-Fox Hills shelf prism. The active tectonic setting and rapid subsidence caused the Lance fluvial and coastal plain deposits to aggrade and accumulate behind the generally rising shoreline trajectory of the Fox Hills Sandstone. The depositional succession is subdivided into 15 clinothem units and the Lance Formation is best exposed in outcrops in clinoforms 10, 11, and 12. Subsurface analysis correlates key stratigraphic surfaces across the basin to define the sediment budget and clinoform architecture. Field analysis along clinoform 12 on the east side of the basin details facies and paleohydraulic dimensions.

Return to top | Return to Index


AN EXAMINATION OF FULL TENSOR GRAVITY GRADIOMETRY DATA : LINKING TENSOR COMPONENTS TO STRUCTURAL FEATURES OF THE VINTON SALT DOME, LOUISIANA

Wesley R. Neely, Bachelor of Science

University of Texas at Austin, May 2014

Supervisor: Clark R. Wilson

74 pages, 13 references, 2 tables

Only over the past two decades has Full Tensor Gravity Gradiometry (FTG) been made available as an alternative geophysical tool for subsurface imaging. This study used an integrated convolution based forward model and layer stripping inversion to improve understanding of the non-vertical tensors, tensor invariants, and limitations of FTG data. Forward model gradients are compared to real data for comparisons of non-vertical tensor components. The signal from the synthetic model is linearly removed via layer stripping from the observed gradients, generating residuals. Residuals are minimized using a simplistic salt dome geometry of a cylindrical body and skewed pyramidal caprock. Invariants are useful interpretation tools that utilize non-vertical tensor components. Results indicate that invariants are useful for identification of structure and shape, whereas non-vertical gradients are beneficial for determining the x, y-location of features. Gravity gradiometry has potential as a supplemental subsurface imaging tool of first order features. Future work includes modifying the complexity of models to account for smaller scale variations in the geologic setting.

Return to top | Return to Index


A SPATIAL DECISION SUPPORT FRAMEWORK FOR WEB-BASED, MULTI-STAKEHOLDER ENGAGEMENT : CASE STUDY OF GEOTHERMAL POWER PROJECT SITING IN IDAHO

Daniel John Noll, MA,, M.GPS

University of Texas at Austin, December 2013

Supervisor: Suzanne A Pierce

140 pages, 97 references, 5 tables

Multi-criteria decision analysis (MCDA) represents an emerging decision aid tool in the field of natural resource decision-making. This thesis involves research into the application of a multi-criteria spatial decisions support system (MOSDSS) to support favorability mapping of geothermal resource potential. The main goal is to provide proof of concept of a tool that can facilitate multi-stakeholder engagement during site selection of a potential power generation facility. It presents information on the history and development of spatial decision support systems in the field of environmental and natural resource decision-making, as well as a case study of a MC-SDSS tool—entitled the "Heatseeker" application— developed and applied to geothermal resource potential in the Eastern Snake River Plain, Idaho. This research was first conducted under a grant from the U.S. Department of Energy National Geothermal Student Competition, The Heatseeker application and supporting infrastructure utilizes a client/server system architecture that provides users with access to spatial and tabular data with low bandwidth requirements. Client-side scripting is used to execute a weighted linear combination (WLC) model and provide users with display and report functionality. Additionally, the tool is optimized for use with a gesture-enabled touch device that serves as a boundary object to facilitate participatory stakeholder engagement. The result of this research is a proof of concept in supporting future MC-SDSS design that can be applied both to geothermal favorability mapping and other natural resource management processes.

This work draws upon the research traditions of multiple academic disciplines, including operations research, computer science, cognitive and behavioral psychology, economics, and public policy. The initial development and application of the MC-SDSS tool involved a team of graduate and undergraduate students from geoscience and social science disciplines. Transdisciplinary approaches to problem structuring and decision-making such as this are an increasingly common approach to natural resource issues.

Return to top | Return to Index


INVESTIGATING PEDOGENIC CARBONATE FORMATION BY MEASURING THE STABLE ISOTOPE COMPOSITION OF WATER IN VERTISOLS

Brandon Jerrod Okafor, Master of Science in Geological Sciences

University of Texas at Austin, May 2014

Supervisor: Daniel O. Breecker

47 pages, 59 references, 3 tables

The oxygen isotope compositions of pedogenic carbonates in paleosols are used to reconstruct paleoelevations, paleoatmospheric circulation, paleotemperatures, and paleoprecipitation. The oxygen isotope compositions of pedogenic carbonates are controlled by temperature and the oxygen isotope composition of soil water, which predominately originates from precipitation. In most calcic soils studied, pedogenic carbonates record the oxygen isotope composition of summer precipitation and/or mean annual precipitation subjected to evaporation. However, due to the complex hydrological properties of Vertiols, which are abundant in the rock record, the isotopic composition of soil water could potentially vary and could influence the isotopic composition of pedogenic carbonate. Furthermore, it is well established that soils contain multiple pools of water with different stable isotope compositions but little work has been done to investigate which pools are recorded by pedogenic carbonates. Therefore, the isotopic composition of soil water in modern Vertisols was monitored and compared with the oxygen isotope composition of pedogenic carbonate in the same soils to investigate if the oxygen isotope composition of pedogenic carbonates in Vertiols record mobile or immobile water.

The isotope composition of soil water was determined in four ways: 1) measurement of isotope composition of water collected by vacuum distillation of soil samples collected by auger, 2) calculation from measured oxygen isotope compositions of soil CO2, 3) calculation from measured oxygen isotope compositions of pedogenic carbonate, and 4) measured isotope compositions of water collected under tension in a soil solution sampler. The oxygen isotope compositions of water in equilibrium with CO2 and water from the solution sampler were indistinguishable at 140cm and were interpreted as mobile water in macropores. The vacuum distilled water (which includes water from a mixture of macropores and micropores) always had lower δ18O values than the macropore water and the other sampling methods, implying the presence of water with low δ18O values. These oxygen isotope compositions of soil water pools were compared with δ18O values of local precipitation (GNIP data from nearby Waco, TX). Below ~100cm, total soil water δ18O values converge to -6.3 ± 0.7 ‰ (1σ, n=20), which is isotopically lighter than the δ18O of mean annual precipitation (MAP) of Waco, Texas (-3.8 ± 2.7 ‰, 1σ, n=96). This could result from recharge of isotopically light September precipitation (SEPT); (-5.9 ± 2.4 ‰, 1?, n=8)) replenishing the soil after dry periods and/or the contribution of winter precipitation (WP) (-5.5 ± 2.4 ‰, 1 σ , n=25). The δ18O values of soil water in equilibrium with soil CO2 ((-4.1 ± 0.8‰) are isotopically similar to or heavier than the isotopic composition of MAP. The δ18O values of soil water in equilibrium with pedogenic carbonate (-2.7 ± 0.9‰) are also isotopically similar to the isotopic composition of summer precipitation (SP, including June, July, and August) (-2.0 ± 2.9 ‰, 1σ, n=8). This suggests that, despite the more complex hydrology of Vertisols compared with other soils orders, the δ18O values of pedogenic carbonates formed in central Texas Vertisols record SP and/or mean annual precipitation that has been subjected to evaporation, just as they do in other soils. If this holds true for Vertisols formed in other climates, then this facilitates the comparison among δ18O values of paleosol carbonates from various soil orders, which is common practice in vertical successions of paleosols. Furthermore, the observation that the δ18O values of water in equilibrium with pedogenic carbonate are more similar to the δ18O values of macropore than micropore water suggests that pedogenic carbonates in central Texas Vertisols may form in macropores. Formation in macropores is more consistent with CO2 degassing and/or evaporation, rather than root water uptake, as a proximal driver of calcite precipitation.

Return to top | Return to Index


REE-BE-U-F MINERALIZATION OF THE ROUND TOP LACCOLITH, SIERRA BLANCA PEAKS, TRANS-PECOS TEXAS

Laurie Christine O’Neill, M.S.GeoSci

University of Texas at Austin, May 2014

Supervisor: J. Richard Kyle

209 pages, 52 references, 4 tables, 2 plates in pocket

Abstract

The Round Top laccolith is considered to be one of the youngest laccoliths in a series of five known as the Sierra Blanca peaks, located in Hudspeth county, Texas. The laccolith is anomalous within the region in that it is peraluminous and enriched in HREEs, F, and U, and is comprised of intermingled discrete packages of various rhyolite types. The laccolith rhyolite varies in color from gray, purple, red, and tan, which combine locally to form distinct geometric mottled textures. The general composition of the rhyolite is 48-52% potassium feldspar, 28-30% quartz, 8-14% plagioclase feldspar, 4-5% annite biotite, 2-3% magnetite-hematite, 1% zircon, and 1% trace phases. The morphology of the trace phases suggests quenching of a late-stage volatile-rich vapor phase at the time of the laccolith formation. The rhyolite displays a wide array of unique mineralogical characteristics indicative to rapid emplacement and metastable crystallization conditions, including three-part quartz phenocrysts, hourglass sector-zoned potassium feldspars, and late-stage anhedral zircons. Unique accessory and trace phases include cassiterite, cerianite-(Ce), changbaiite, columbite, cryolite, tantalite, thorite, yttrofluorite, yttrocerite, and two unidentified minerals named (W) and (X).

Initial alteration of the laccolith by high temperature volatile-rich vapor during the late stages of crystallization caused the partial dissolution of the feldspars and quartz. Subsequent quenching of this high temperature vapor phase produced the abundant interstitial, and pore filling REE-fluorides common to the laccolith. The variation in rhyolite color and the presence of the mottled textures are a direct result of partial oxidation of the laccolith by secondary fluids. The oxidizing fluids migrated within the laccolith along an extensive fracture network, altering the adjacent wallrock by oxidizing magnetite phenocrysts to hematite. The gray, purple, and red rhyolite types reflect an increase in turbidity caused by hematitic inclusions primarily within the pore spaces of the potassium feldspar portions of the groundmass. The tan rhyolite is locally restricted to the base of the laccolith and has been subjected to an intense degree of alteration independent of the other rhyolite types, primarily indicated by the conversion of feldspars to clay.

Petrographic, microbeam, and geochemical studies have determined little variation in REE concentration between the three rhyolites of similar alteration intensity, but have indicated a depletion in LREEs within the more altered tan rhyolite. The average REE+Y content for the rhyolites sampled (n=11) ranges between 249 ppm and 518 ppm. The REE+Y concentrations between rhyolite samples of the same type show some variation, possibly indicating a correlation between alteration and REE+Y abundance and/or innate heterogeneity in the vapor phase during the initial laccolith formation.

The magma emplaced at Round Top underwent a prolonged evolutionary process of fractionation/differentiation as evident by the unusual mineral assemblage and geochemical enrichment associated with the laccolith (e.g. extremely negative europium anomaly, and the positive La/Yb correlation). Future exploration for Round Top style REE-deposits should center within long-lived, tectonically active and complex regions where laccoliths are likely to exist. Specifically, exploration should focus on identifying the youngest laccolith in a felsic series, as this is the most likely to contain the greatest abundance of incompatible elements within the laccolithic group. The early alteration of feldspars by the high temperature vapor phase was crucial in the development of the REE+Y enrichment at Round Top. The feldspar dissolution provided abundant open pore space that was subsequently filled by the REE-fluorides. Thus, exploration should additionally seek laccoliths that have undergone a similar early alteration process, and expand to potential laccolith groups not yet exposed by erosional processes.

Return to top | Return to Index


OUTCROP ANALYSIS OF OOID GRAINSTONES IN THE PERMIAN GRAYBURG FORMATION, SHATTUCK ESCARPMENT, NEW MEXICO

John Alexandre Parker, M.S.Geo.Sci.

University of Texas at Austin, May 2013

Supervisor: Charles Kerans

130 pages, 54 references, 2 tables

Ooid grainstone reservoir architecture remains poorly understood, particularly because of sedimentologic and stratigraphic heterogeneities that are innate to grainstone body development. Understanding of Geospatial relationships and recovery of hydrocarbons from these significant reservoir facies can be improved with access to outcrop analog information from well exposed examples.

Object-based models and other modern subsurface reservoir models are considered superior methods for portraying realistic sediment distributions. These models, however, are highly dependent on input data describing sediment-body geometry for faithful template generation. Such input data are notably rare in carbonate systems. Maps generated from modern depositional patterns give a first approximation of areal distribution, but they are not as useful for understanding final preserved stratigraphic thickness and internal facies, sedimentary structure, and grain-type patterns. For this purpose, studies of exceptional outcrops are required. The 18 km long oblique-dip-oriented wall of the Shattuck Escarpment provides such a unique exposure of Permian-age grainstones.

The Shattuck Escarpment in the Guadalupe Mountains provides an oblique-dip profile that exposes a near-complete middle Permian Grayburg mixed clastic-carbonate shelf succession of three high-frequency sequences which contain 30 high-frequency cycles. Particularly important for this study are the four cycles that display full updip to downdip extents of ooid grainstone tidal bar and tidal delta objects. The data from the Shattuck wall presented in this paper focusses on the transgressive portion of the upper Grayburg, or G12 high-frequency sequence (HFS), located 5 km landward of the time-equivalent shelf margin. This interval is an analog for productive fields along the northwest shelf of the Delaware Basin and on the eastern flank of the Central Basin Platform. The goal of this project is to understand the sedimentology and facies/cycle architectural variability of tidally influenced shelf crest ooid grainstones of the Grayburg Formation. Comparing this outcrop data to modern grainstone deposits allows the reader to understand the small-scale and large-scale sedimentologic and architectural patterns in analogous subsurface ooid grainstone reservoirs.

Spatial analysis of these cycles was carried out using measured sections and GigaPan (high resolution photomosaic) data. Petrophysical (Porosity and Permeability) data was collected from three separate vertical core plug transects approximately 1 km apart with a vertical resolution of 30 cm. Cycle-set-scale grainstone complexes up to 6m thick extend at least 4.25 km along depositional dip and show variations in permeability between 6-400 mD and porosities between 8-20% within the lower portions of the grainstone complex.

Return to top | Return to Index


TAXONOMY AND PHYLOGENY OF THE AETOSAURIA (ARCHOSAURIA: PSEUDOSUCHIA) INCLUDING A NEW SPECIES FROM THE UPPER TRIASSIC OF ARIZONA

William Gibson Parker, Jr. Ph.D

University of Texas at Austin, May 2014

Supervisor: Timothy Rowe

459 pages, 306 references, 1 table

Aetosaurians are a clade of pseudosuchian archosaurs that were globally dispersed during the Late Triassic Epoch. Aetosaurians are characterized by a suite of osteoderms that covered much of the body. These osteoderms are commonly recovered as fossils and possess characteristic surface ornamentation that can be diagnostic for taxa. The abundance of these osteoderms and the ease of identification have made aetosaurians ideal index taxa for Late Triassic biostratigraphy. Of special interest are specimens from South and North America and Europe that have been assigned to the genus Stagonolepis, which have been utilized for correlation of continental sedimentary units and to approximately date the timing of important biotic events. New finds have called the synonymy of these Stagonolepis-like specimens into question, jeopardizing their ability to serve as biochronological markers. Detailed examination of all of the specimens assigned to Stagonolepis robertsoni demonstrates that all of these specimens do not represent the same species. The South American material is assigned to the genera Aetosauroides, Aetobarbakinoides, and Polesinesuchus; the European material to Stagonolepis; and the North American material to Calyptosuchus, Adamanasuchus, and a newly recognized taxon, Scutarx deltatylus. Scutarx deltatylus can be differentiated from other aetosaurians by the presence of a strongly raised, triangular boss, on the posteromedial corner of the paramedian osteoderms. Scutarx deltatylus also preserves the first good skull material from a Stagonolepis-like aetosaur from North America. A dorsoventrally thickened skull roof and an anteroposteriorly short parabasisphenoid further demonstrate the distinctness of this material from that of South America and Europe. A detailed phylogenetic analysis of all known aetosaurians further demonstrates the distinctness of these taxa. This new expanded analysis of 28 taxa and 83 characters recovers Aetosauroides scagliai as the sister taxon to all other aetosaurians. Stagonolepis robertsoni from Scotland does not clade with Stagonolepis olenkae from Poland. Calyptosuchus wellesi is the sister taxon to a clade consisting of Scutarx deltatylus and Adamanasuchus eisenhardtae. However, distribution of autapomorphies across these taxa precludes them from being synonymized. As a result the Stagonolepis-like aetosaurs cannot be used for global scale correlations of Upper Triassic strata, but do appear to be of utility for regional correlations, in particular those between the Chinle Formation and Dockum Group in the American Southwest.

Return to top | Return to Index


TITLE

Brittney Maryah Pollard, M.S. Geo. Sci.

University of Texas at Austin, May 2014

Supervisor: Sharon Mosher

300 pages, 137 references, 38 tables

Discrete (mm- to m-scale) mylonitic shear zones in the northeastern Harquahala metamorphic core complex, Arizona, show evidence of fluid-mineral interactions catalyzing deformation and metamorphism. Many contain a deformed central epidote vein with adjacent bleached haloes and flanking paired shear zones that indicate significant fluid-rock interaction during deformation. An integration of structural and geochemical methods was employed to understand timing, metamorphic conditions, and physiochemical processes responsible for producing the discrete shear zones. Field and microstructural evidence suggest the zones initiated on antecedent fractures. Electron backscatter diffraction (EBSD) analyses show a significant coaxial contribution to the shear, and quartz deformation predominately by prism slip, along with some rhomb slip, suggesting amphibolite-facies conditions during shearing. Fourier Transform Infrared spectroscopy analyses of quartz reveal higher water contents within shear zones than within country rocks, indicating fluid infiltration synchronous with shearing. Stable isotope analyses of quartz and feldspar from mylonites are consistent with an igneous or metamorphic fluid origin.

Microstructural observations suggest that the zone morphology with epidote veins, bleached haloes, and flanking discrete paired shear zones was developed predominantly from reaction softening mechanisms. The increase in deformation from bleached rock to flanking shear zones is marked by progressive modal increases in biotite and myrmekite, and modal decreases in K-feldspar, and locally epidote and titanite. Myrmekitic textures recrystallized readily and resulted in progressively greater grain size reduction of feldspar, which aided in the progressive alignment and linkage of the biotite grains, which together concentrated the deformation in bands. Volume reduction resulting from some of the metamorphic reactions may have led to a positive feedback cycle among fluid infiltration, metamorphism and deformation. U-Pb isotope analyses of syn-metamorphic titanite yield an age of ~70 Ma, suggesting the shear zones formed during cooling of the Late Cretaceous (75.5±1.3 Ma) Brown’s Canyon pluton, consistent with their top-to-the-southwest sense of shear, rather than during top-to-the-northeast directed Miocene metamorphic core complex exhumation.

Petrography, EBSD analyses, and U-Pb dating of titanite from other (non-discrete) mylonites in the area imply most formed synchronously with the discrete shear zone mylonites. Only rare, scattered mylonites show features consistent with metamorphic core complex exhumation.

Return to top | Return to Index


NATURAL FRACTURE CEMENTATION IN THE MARCELLUS FORMATION

Laura Elizabeth Pommer, M.S. Geo. Sci.

University of Texas at Austin, May 2013

Supervisors: Julia Gale and Peter Eichhubl

292 pages, 110 references, 11 tables

In order to test the hypothesis that fractures in outcrops are equivalent to subsurface fracture systems I compare fracture cement morphology, texture, mineralogy and geochemistry from a suite of outcrop samples from Union Springs, NY, with fractures in four cores from a currently producing reservoir in southwest Pennsylvania. Transmitted light-microscope petrography and cold cathodoluminescence of calcite of outcrop and core samples reveals a variety of cement morphologies including crack-seal and blocky fracture cement textures that are interpreted as a record multiple repeated stages of fracture opening and sealing, as well as fibrous calcite fill and other mineral phases. The stable isotopic composition of calcite fracture cements from different fracture types in cores and outcrop range from -21.5 to +4.4‰δ13C PDB and -8.0 to -12.0 ‰ δ18O PDB and indicate calcite precipitation temperatures between 46 and 89°C. Fluid inclusion microthermometry from secondary fluid inclusions indicates trapping temperatures between 110 and 120°C. Microprobe analysis of fracture calcite cement indicates a range in Fe, Mn, and Mg composition, with subsurface and outcrop cement of similar composition. Assuming burial history predicts thermal history, isotopic compositions together with fluid inclusions suggest calcite precipitated in vertical fractures during prograde burial, during the Acadian to early Alleghanian orogenies. These findings indicate that fractures in outcrops of the Marcellus Formation can be used as a proxy for those in the subsurface.

Return to top | Return to Index


QUANTITATIVE ASSESSMENT OF PORE TYPES AND POROSITY DISTRIBUTION ACROSS THERMAL MATURITY, EAGLE FORD FORMATION, SOUTH TEXAS

Maxwell Elliott Pommer, MSGeoSci

University of Texas at Austin, August 2014

Supervisor: Kitty L. Milliken

208 pages, 88 references, 7 tables

Scanning electron microscopy of Ar-ion milled samples from the Eagle Ford Formation, South Texas shows that the character and abundance of porosity changes significantly across burial conditions as a result of compaction, cementation, bitumen generation, and generation of secondary porosity within organic matter (OM). Samples displaying a range of compositions and maturities are imaged and quantified to provide insight into the effects of these processes.

Porosity in low-maturity samples (Ro~0.5%) is volumetrically dominated (0.1% -12.5% bulk volume, average 6.2%) by relatively large, mostly interparticle, primary mineral-associated pores (median sizes range 35.9-52.7 nm). Larger pores are generally associated with coccolith debris that is commonly aggregated into pellets. Porosity and pore size correlate directly with calcite abundance and inversely with OM volumes. OM is dominantly detrital kerogen "stringers" that range in size and have spatial distributions and character suggestive of detrital origin. Destruction of primary porosity in low-maturity samples has occurred due to compaction of ductile kerogen and clays and, to a minor degree, as a result of cementation and infill of early bitumen.

Smaller, secondary OM-hosted pores (median size range 11.1-14.9 nm) volumetrically dominate porosity (0.02%-3.6% bulk volume, average of 1.36%), in most high-maturity samples (Ro~1.2%-1.3%). Mineral-associated pores are present, but are typically smaller (median size range from 20.3-40.6 nm) and less abundant (0.0%-10.0% bulk volume, average of 2.5%) than at low maturity. Abundant mineral-associated porosity is present locally in samples where incursion of primary pore space by bitumen has not occurred. OM within high-maturity samples is distributed more evenly throughout the rock fabric, occupying spaces similar in size and morphology to primary interparticle pores, coating euhedral crystals (probable cements), and filling intraparticle porosity. These observations, and positive correlation between calcite and OM volumes (OM-hosted pore volume included) in samples with dominantly OM-hosted pore networks, suggests that a large portion of OM within high-maturity samples is diagenetic in origin and has filled primary pore space. Destruction of primary porosity in high-maturity samples has occurred through cementation, bitumen infill, and, possibly greater compaction. Additional porosity, however, has been generated through maturation of OM.

Return to top | Return to Index


USING ANALYTICAL AND NUMERICAL MODELING TO ASSESS DEEP GROUNDWATER MONITORING PARAMETERS AT CARBON CAPTURE, UTILIZATION, AND STORAGE SITES

Sean Laurids Porse, M.S.Geo.Sci.

University of Texas at Austin, December 2013

Supervisor: Michael H. Young

144 pages, 103 references, 5 tables

Carbon Dioxide (CO2) Enhanced Oil Recovery (EOR) is becoming an important bridge to commercialize geologic sequestration (GS) in order to help reduce anthropogenic CO2 emissions. Current U.S. environmental regulations require operators to monitor operational and groundwater aquifer changes within permitted bounds, depending on the injection activity type. We view one goal of monitoring as maximizing the chances of detecting adverse fluid migration signals into overlying aquifers. To maximize these chances, it is important to: (1) understand the limitations of monitoring pressure versus geochemistry in deep aquifers (i.e., ›450 m) using analytical and numerical models, (2) conduct sensitivity analyses of specific model parameters to support monitoring design conclusions, and (3) compare the breakthrough time (in years) for pressure and geochemistry signals. Pressure response was assessed using an analytical model, derived from Darcy’s law, which solves for diffusivity in radial coordinates and the fluid migration rate. Aqueous geochemistry response was assessed using the numerical, single-phase, reactive solute transport program PHAST that solves the advection-reaction-dispersion equation for 2-D transport. The conceptual modeling domain for both approaches included a fault that allows vertical fluid migration and one monitoring well, completed through a series of alternating confining units and distinct (brine) aquifers overlying a depleted oil reservoir, as observed in the Texas Gulf Coast, USA. Physical and operational data, including lithology, formation hydraulic parameters, and water chemistry obtained from field samples were used as input data. Uncertainty evaluation was conducted with a Monte Carlo approach by sampling the fault width (normal distribution) via Latin Hypercube and the hydraulic conductivity of each formation from a beta distribution of field data. Each model ran for 100 realizations over a 100 year modeling period. Monitoring well location was varied spatially and vertically with respect to the fault to assess arrival times of pressure signals and changes in geochemical parameters.

Results indicate that the pressure-based, subsurface monitoring system provided higher probabilities of fluid migration detection in all candidate monitoring formations, especially those closest (i.e., 1300 m depth) to the possible fluid migration source. For aqueous geochemistry monitoring, formations with higher permeabilities (i.e., greater than 4 x 10-13 m2) provided better spatial distributions of chemical changes, but these changes never preceded pressure signal breakthrough, and in some cases were delayed by decades when compared to pressure. Differences in signal breakthrough indicate that pressure monitoring is a better choice for early migration signal detection. However, both pressure and geochemical parameters should be considered as part of an integrated monitoring program on a site-specific basis, depending on regulatory requirements for longer term (i.e., ›50 years) monitoring. By assessing the probability of fluid migration detection using these monitoring techniques at this field site, it may be possible to extrapolate the results (or observations) to other CCUS fields with different geological environments.

Return to top | Return to Index


CHLORINE AND HYDROGEN ISOTOPE GEOCHEMISTRY OF OBSIDIAN GLASSES : BEHAVIOR DURING VOLCANIC DEGASSING AT MONO CRATERS, CA

Timothy John Prather, Bachelor of Science

University of Texas at Austin, May 2013

Supervisor: Jaime Barnes

34 pages, 28 references, 1 table

Volatile concentrations (Cl, H2O, and CO2) and stable isotope compositions (δD and δ37C1) of volcanic glasses (obsidians) have been determined to quantify the behavior of chlorine stable isotopes (35C1 and 37C1) during volcanic degassing. Pyroclastic obsidian clasts (n = 27), collected from tuff layers representing a single eruptive sequence that occurred circa 1350 A.D., as well as rhyolitic obsidian samples (n = 12) collected from the high-silica (‹70% Si) flows forming the domes and coulees in the region, were collected from the Mono Craters volcanic field, California. The Cl, H2O, and CO2 concentrations recorded by these eruptive air-fall obsidians track the chemical evolution of the magmatic system during eruption, whereas the concentrations of the dome samples represent the final degassed product. The H2O and CO2 concentrations of the air-fall samples range from 0.49 to 2.13 wt% and 2 to 35 ppm, respectively; whereas concentrations in the dome glasses range from 0.17 to 0.33 wt% and 1 to 3 ppm, respectively. H2O and CO2 concentrations in the air-fall samples and dome samples are strongly correlated and reflect the degassing trend of the eruptive sequence. Air-fall obsidians were selected from two tuff layers: 1) a lower layer containing average H2O and CO2 concentrations of 1.5 ± 0.4 wt% and 20 ± 7 ppm, respectively, and 2) an upper layer containing slightly lower average H2O and CO2 concentrations of 0.9 ± 0.4 wt% and 5 ± 3 ppm, respectively. Dome obsidians were selected from three rhyolitic flows in the region, Panum Crater Dome, North Coulee, and Northwestern Coulee, containing average H2O and CO2 concentrations of 0.27 ± 0.06 wt% and 2 ± 1 ppm, respectively. Chlorine concentrations of the air-fall samples range from 609 to 833 ppm and do not display a strong correlation with either H2O or CO2 concentrations. Chlorine concentrations are essentially identical between the two layers, averaging 746 ± 57 ppm m the lower layer and 703 ± 73 ppm in the upper layer.

δD values of the air-fall obsidians vary between -62 to -84‰ (lσ = ±2‰), whereas the dD values of the dome obsidians vary between -99 to -107‰, and display D/H ratios that decrease with lower total water content following a distillation trend dominated by open system degassing. δ37Cl values were measured on samples from each of the two tuff layers and from the domes. The samples from the lower layer have δ37Cl values between -2.0 to -0.1 ‰(n = 12), whereas the samples from the upper layer have δ37C1 values between -1.5 and -0.1‰ (n = 12) (la = ±0.2‰). δ37C1 values of domes samples range from -1.2 to 0.0‰ (n = 10). overlapping the range in δ37Cl values in the air-fall samples.

The lack of systematic correlation between the measured δ37C1 values and any of the other measured parameters (H2O, CO2, Cl concentrations, δD values) during the characteristic degassing sequence exhibited by the obsidian air-fall clasts and the dome obsidians indicates that chlorine stable isotopes likely do not fractionate during volcanic degassing. The wide range in δ37C1 composition may be indicative of heterogeneity of chlorine stable isotopes in the magma source.

Return to top | Return to Index


CONTROLS ON LATE NEOGENE DEEP-WATER SLOPE CHANNEL ARCHITECTURE IN A BATHYMETRICALLY COMPLEX SEAFLOOR SETTING : A QUANTITATIVE STUDY ALONG THE SOUTHEASTERN CARIBBEAN PLATE MARGIN, COLUMBUS BASIN, TRINIDAD

Kristie Anuradha Ramlal, M.S. Geo.Sci.

University of Texas at Austin, December 2013

Supervisor: Lesli J. Wood

97 pages, 61 references

Slope-channels act as conduits that transport sediments from the shelf staging area to the basin floor. The Pliocene-Pleistocene section of the Columbus Basin in the deep-water slope offshore eastern Trinidad provides an opportunity to study slope-channel morphology and evolution, as well as any association between deep-water deposits, palaeo-seafloor bathymetry, shelf sediment feeder mechanism and changes in sediment supply types and volumes. Approximately 3250 km2 of 3D seismic data allow imaging and interpretation of channels within an interval between two regional surfaces termed P30 and P40. Observations of seismic cross-sections and stratal slices reveal a number of features including channels, mud diapirs, mass transport deposits (MTDs), and faulted anticlinal ridges. Channels appear leveed and unleveed, and alternate with MTDs in a cyclic vertical succession. Nineteen channels were mapped and divided into two groups based on their degree of levee development and stratigraphic position relative to MTDs. Group 1 channels, positioned below MTDs near the base of the interval, are shallowly incised, and show limited levee development. Group 2 channels, situated above MTDs, are relatively deeply incised, and have comparatively larger, well-developed levees throughout their lengths. Morphometric data from these channel groups reveal significant variability in channel width, channel depth, meander belt width, and sinuosity downslope. This variability is associated with influences of temporally equivalent local features and regional sea-floor slope changes. Increased slope gradient causes a marked increase in sinuosity. Diapirs and anticlinal ridges confine channel paths, divert their flow, and cause post-depositional deformation of both levees and channels. Levee height decreases downslope while levee width shows considerable asymmetry, which is related to occurrences of mud diapirism and MTDs. Irregularities on the upper surface of MTDs create accommodation space that confines turbidity flows, enabling ponding of sediments and volumetrically large levee construction. This accounts for dispersion of turbidity flows below the MTD which creates a series of small channels spread over a wide area, and comparatively fewer, confined channels above the MTDs with large levees.

Return to top | Return to Index


THE ROLE OF THE MEXICAN PLATEAU IN SHAPING RAINFALL OVER TEXAS

Tong Ren, M S Geo Sci

University of Texas at Austin, December 2013

Supervisor: Rong Fu

38 pages, 33 references, 1 table

Previous studies have suggested that advection from the Mexican Plateau (MP) may influence rainfall over Texas in spring and summer; generally air ascends over the cordillera and descends over the southern plains. The two mechanisms may link the northern Mexico drought to Texas drought. Observations and the Community Earth System Model are used in this study to describe the 2011 Texas-northern-Mexico drought and examine the role of the MP on the hydro-climate over the southern US, providing implications for the linkage between the MP and rainfall over Texas. A control run and three experimental runs were performed with prescribed sea surface temperatures and sea ice fractions. The results show that when the MP becomes dry, rainfall declines locally and downstream. During the spring, the dry air brought to Texas by prevailing westerly winds suppresses local convection; but dry air advection from the highlands has little influence on rainfall over Texas during the summer when Texas is no longer in the downstream areas. During the summer, a warmer MP draws moist air over the peripheral low elevation areas to the highlands; it bends the low-level jet towards the highlands and an anti-cyclonic flow anomaly forms over the southern US, which causes air to diverge and tends to reduce rainfall over the southern US.

Return to top | Return to Index


THERMOCHRONOMETRIC INVESTIGATION OF THE PALEOZOIC STRATIGRAPHIC AND THERMAL EVOLUTION OF THE WESTERN DESERT, EGYPT

Caleb Hayes Rhatigan, M.S. Geo. Sci.

University of Texas at Austin, May 2013

Supervisor: Daniel Stockli

131 pages, 55 references

The northeast African continental margin of the Western Desert of Egypt is host to a complexly deformed series of Phanerozoic basins. Substantial sedimentary deposition (~5 km) and basin formation resulted from regional deformation due to continental colli¬sion and repeated rifting and inversion cycles. Limited sedimentary exposure and explora¬tion has prevented elucidation of Phanerozoic basin evolution, particularly in the Paleozoic. Previous studies of the region have largely relied upon sedimentary analysis, gravity, and 2D/3D seismic data. This study, in contrast, has employed extensive use of detrital zircon (U-Th)/He thermochronology (n=1004) from 17 wells in conjunction with 3D seismic, well log correlation, and heat flow data to elucidate a spatiotemporally comprehensive tectonic and stratigraphic model.

The detrital zircon thermochronometric data provides new evidence that the lower Paleozoic, Carboniferous, and Mesozoic stratigraphic sequences of the Western Desert represent thermally distinct, tectonically controlled sequences with independent thermal evolutions. The lower Paleozoic sequence has been partially thermally reset, reaching temperatures of ~140-170°C. Partial resetting is noted throughout the region and reached its thermal maximum in the Permo-Triassic, synchronous with onset of Neotethyan rifting. The Carboniferous sequence has not been thermally reset, with exposure to temperatures no greater than ~140°C and reaching thermal maximum presently. Carboniferous (U-Th)/He ages have dominant input from short-lag-time zircons (exhumation to deposition) and indicate the stratigraphic sequence was proximally sourced. The proximal sourcing is likely from transmitted stress and fault reactivation in Egypt during the Hercynian Oroge¬ny that caused fault block exhumation and erosional unroofing. Sediment was shed from uplifted fault blocks that formed the eastern boundary of the Carboniferous sequence. The Mesozoic sequence has not been thermally reset, reaching temperatures no greater than ~120°C and presently reaching thermal maximum.

Localized areas with stacking of lower Paleozoic, Carboniferous, and Mesozoic sequences likely bury the lower Paleozoic to abnormally deep depths (~7 km) and elevated temperatures of ~200°C. Evidence from faulting relationships, basin controlling structures, and heat flow data indicate that N-S trending basement structures may define a region of crustal transition between the Archean-Paleoproterozoic Saharan Metacraton and the juvenile Arabian-Nubian Shield.

Return to top | Return to Index


IDENTIFYING AND MAPPING CLAY-RICH INTERVALS IN THE FAYETTEVILLE SHALE : INFLUENCE OF CLAY ON NATURAL GAS PRODUCTION INTERVALS

Forrest Daniel Roberts, M.S. Geo.Sci

University of Texas at Austin, December 2013

Supervisors: Scott W. Tinker and William L. Fisher

43 pages 35 references, 2 tables

The Fayetteville Shale is composed dominantly of clay, carbonate, and siliciclastic minerals. A variety of facies have been described by other workers and in this study, defined by mineral content, biota, fabric, and texture. Because the Fayetteville Shale is one of the top shale-gas producing plays in the U.S., an inquiry into key drivers of good-quality production is worthwhile. In particular, a hypothesis that intervals of high clay content should be avoided as production targets is investigated in this study. A high level of separation between wire-line log neutron porosity (NPHI) and density porosity (DPHI) in the Fayetteville Shale is observed in contrast to the wire-line log responses from the Barnett and Haynesville Shales. Clay minerals have a significant effect on NPHI, which in turn affects separation between NPHI and DPHI (PHISEP). X-Ray Diffraction (XRD) clay data was available for three wells, and efforts to correlate XRD results to PHISEP led to establishing NPHI as a reasonable proxy for clay. Using NPHI as a proxy it was possible to pick clay-rich intervals, map them across the study area, and to determine net clay in the Fayetteville Shale. Maps of net clay-rich intervals were compared to a map of production, but revealed no obvious correlation. Stratigraphic cross-sections showing the clay-rich intervals revealed a clay-poor interval in the upper part of the lower Fayetteville. This interval is the primary target for horizontal well completion. It is bounded above and below by more clay-rich intervals. Establishing the clay-rich intervals via porosity log separation (PHISEP) is one tool to help determine possible stratigraphic zones of gas production and can lead to a better understanding of intervals in which to expect production.

Return to top | Return to Index


ANTHROPOGENIC IMPACTS ON RECHARGE PROCESSES AND WATER QUALITY IN BASIN AQUIFERS OF THE DESERT SOUTHWEST: A COUPLED FIELD OBSERVATION AND MODELING STUDY

Wendy Marie Robertson, Ph.D.

University of Texas at Austin, May 2014

Supervisor: John M. Sharp Jr.

169 pages, 181 references, 17 tables

The development of natural grass/scrubland for agricultural use within the Trans-Pecos basins has altered recharge mechanisms and raised questions about groundwater sustainability. Past efforts focused on recharge in arid basin systems used three main assumptions: there is minimal modern recharge, no widespread recharge on basin floors, and no recharge from anthropogenic sources. However, in the Trans-Pecos, nitrate (NO3-) concentrations have increased in basin groundwater (up by 3-4 mg/l as NO3- in 40 yrs), refuting the “classic” model and posing water quality risks. Grazing and irrigated agriculture have impacted basin hydrology by altering vegetation regime and the magnitude and spatial distribution of infiltration. This has increased recharge, Cl-, and mobile N flux to basin groundwater. A series of spatially-distributed net infiltration models were used to estimate potential recharge from natural and anthropogenic sources. Between 7-20% of potential recharge results from widespread recharge on the basin floors. Additionally, from 1960-2000, irrigation return flow may have contributed 3.0 × 107 - 6.3 × 107 m3 of recharge. These results are supported by field observations. Cores collected beneath agricultural land document changes in water content and pore water chemistry that imply increased downward flux of moisture and solute, and NO3- and Cl- inventories beneath irrigated land are distinct in amount and profile from those in natural areas. There are significant implications for sustainability based upon the trends in groundwater NO3- concentrations, core results, and net infiltration models: more recharge may enter the basins than previously estimated and there is a potential long-term concern for water quality. Due to thick unsaturated zones in the basins, long travel times are anticipated. It is unknown if NO3- and Cl- flux has peaked or if effects will continue for years to come. Further study should be undertaken to examine anthropogenic impacts on basin water quality. Additionally, these impacts may occur in similar systems globally and there is considerable evidence for the re-evaluation of the validity of the “classic” model of recharge in arid basin systems. Future studies and management plans should incorporate potential impacts of changes in vegetation and land use on recharge processes and water budgets in arid basins.

Return to top | Return to Index


CHALLENGES AND OPPORTUNITIES FOR THE DEVELOPMENT OF SHALE RESOURCES IN COLOMBIA

Juan Camilo Rodriguez Sanchez, M.S.E.E.R.

University of Texas at Austin, December, 2013

Supervisor: William L. Fisher

83 pages, 75 references, 11 tables

After the success of shale gas development in the United States, countries around the world are looking within their own territories for the possibility of replicating the U.S successes in order to achieve financial and/or energy security objectives. Such enterprise has shown to be not as easy as it might have been perceived to be. Some countries like Argentina, China and Poland, where large reserves of shale resources have been identified, have struggled to obtain beneficial results from their shale operations, with the result that even the more optimistic operators are now showing more caution and are reviewing everything before making any commitments to operate in countries with identified shale resources.

Colombia, a country with strong oil and gas roots in its economic history, is actively attempting to attract operators to explore and produce their shale resources. If successful, these efforts have the potential to bring increased foreign investment to the country, while also improving Colombia's oil and gas reserves, which have been declining over the last five years. This thesis, will address the challenges and opportunities of the development of shale resources in Colombia that operators will face by reviewing several critical aspects of the process. This thesis begins with a discussion of the geology of shale resources in Colombia, followed, first, by a review and analysis of the fiscal and contractual regime established in Colombia for the oil and gas industry, then, second, a risk analysis of possible Colombian shale operations, then third, a financial analysis of a possible shale project and, finally, ends with a summary of the challenges and opportunities an operator could face based on the analysis of the previous topics.

Return to top | Return to Index


ANALYSIS OF GPU-BASED CONVOLUTION FOR ACOUSTIC WAVE PROPAGATION MODELING WITH FINITE DIFFERENCES : FORTRAN TO CUDA-C STEP-BY-STEP

Makoto Sadahiro, M.S.Geo.Sci.

University of Texas at Austin, May 2014

Supervisors: Paul L. Stoffa, Robert H. Tatham

72 pages, 6 references

By projecting observed microseismic data backward in time to when fracturing occurred, it is possible to locate the fracture events in space, assuming a correct velocity model. In order to achieve this task in near real-time, a robust computational system to handle backward propagation, or Reverse Time Migration (RTM), is required. We can then test many different velocity models for each run of the RTM. We investigate the use of a Graphics Processing Unit (GPU) based system using Compute Unified Device Architecture for C (CUDA-C) as the programming language. Our preliminary results show a large improvement in run-time over conventional programming methods based on conventional Central Processing Unit (CPU) computing with Fortran. Considerable room for improvement still remains.

Return to top | Return to Index


THE IMPACT OF SHELF MARGIN GEOMETRY AND TECTONICS ON SHELF-TO-SINK SEDIMENT DYNAMICS AND RESULTANT BASIN FILL ARCHITECTURES

Migdalys Beatriz Salazar. Ph.D.

University of Texas at Austin, May 2014

Supervisor: Lesli J. Wood

215 pages, 117 references, 16 tables

This dissertation focuses on understanding the relative importance of external (eustacy) versus local tectonic and sedimentary processes in controlling continental-margin depositional architectures and their implications for sediment distribution. The emphasis of this study is the interpretation of clinoform geometries and stratigraphic relationships observed on 3D and 2D seismic reflection data in the Taranaki Basin, which is characterized by a variety of clinoform architectures on its Pliocene-Recent margin (Giant Foresets Formation). I combined seismic stratigraphic interpretations and biostratigraphic studies using a dataset that consists of 1,700 km2 of 3D seismic lines, 4,000 km of 2D regional seismic lines, and data from six wells. The study was divided into three sections. First, three major stages of clinoform evolution were identified based on their architectural and geomorphological characteristics. Isochron maps were generated to identify correlations between stratigraphy and paleostructures, and seismic attribute maps were elaborated to identify and characterize geological features and depositional elements. In the second phase of the study, 2D stratigraphic forward modeling techniques were applied in an effort to quantitatively determine the relative importance of the mechanisms acting in the basin (eustacy, tectonism and sediment supply). Finally, a similar approach was applied using clinoform morphologies in the eastern Trinidad margin where the tectonic configuration of the basin was completely different to the one in the Taranaki Basin. The objective was to compare the results in a region with different a tectonic setting to validate the applicability of the methodology in other basins worldwide.

The results of this research indicate that the methodology that was developed for the quantitative analysis of clinoform architectures in the Taranaki Basin is applicable to other basins worldwide and that the work flow provides a more comprehensive understanding of the factors that influence continental margin development. Generic observations of this research showed that (1) underlying structures in the shelf and slope area can play an important role in influencing the location and morphology of the shelf edge area and controlling sediment distribution; (2) high sediment supply, along with accommodation, play a key role in the construction of high-relief clinoforms and earlier dispersal of sediments into deep water; and (3) lateral variations associated with high sediment discharge sources (e.g. paleo Orinoco shelf-edge delta) can generate important changes in continental-scale clinoform architectures alongstrike in continental margins influence sediment distribution patterns in the deep-water component of the basin.

Return to top | Return to Index


QUATERNARY SLIP TRANSFER BETWEEN THE BANNING AND MISSION CREEK FAULTS OF THE SOUTHERN SAN ANDREAS FAULT, SOUTHERN CALIFORNIA

Aaron Zachary Salin, Bachelor of Science

University of Texas at Austin, May, 2014

Supervisor: Whitney M. Behr

78 pages, 37 references

The southern San Andreas fault (sSAF) poses a significant hazard to large population centers, yet is the section of the fault that is least understood. Its lack of historic rupture makes understanding the potential dynamics of a fault rupture key for seismic hazard assessments and preparedness. Recent slip rate data for the Mission Creek strand in the Indio Hills suggests that it is the primary carrier of ruptures through the northern Coachella Valley, but there is a deficit of studies to assess the validity of that claim. This work aims to close that knowledge gap by answering two questions about the Banning and Mission Creek strands of the sSAF: 1) Is there a difference between offsets that provide us information about relative activities, and thus likelihood of rupture, of the two faults? 2) If so, what structures accommodate the transfer of slip from one fault to the other? We address these questions using high-resolution imaging technology (LiDAR DEMs) and a field-based structural analysis of the Indio Hills area. Observations from 41 offset features and a number of non-offset features show decreasing trends in offset for among similar sized drainages on the Mission Creek fault, while offsets along the Banning fault increase away from the Indio Hills. This finding implies that some slip is being transferred through the Indio Hills onto the Banning. We also find a range of structures which have accommodated this slip transfer in the form of transpressive uplift between two faults which merge at depth.

Return to top | Return to Index


INVESTIGATING THE EFFECT OF HIGH-ANGLE NORMAL FAULTING ON UNROOFING HISTORIES OF THE SANTA CATALINA-RINCON AND HARCUVAR METAMORPHIC CORE COMPLEXES, USING APATITE FISSION-TRACK AND APATITE AND ZIRCON (U-TH)/HE THERMOCHRONOMETRY

Sean Michael Sanguinito, M.S. Geo. Sci.

University of Texas at Austin, Month Year

Supervisor: December 2013

191 pages, 109 references, 21 tables

The formation and evolution of metamorphic core complexes has been widely studied using low temperature thermochronometry methods. Interpretation of these data has historically occurred through the lens of the traditional slip rate method which provides a singular rate that unroofing occurs at temporally as well as spatially, and assumes unroofing is dominated by motion on a single master detachment fault. Recently, several new studies have utilized (U-Th)/He ages with a higher spatial density and greater nominal precision to suggest a late-stage rapid increase in the rate of unroofing. This analysis is based on the traditional slip rate method interpretation of broad regions of core complexes that display little to no change in age along the slip direction. An alternative interpretation is presented that instead of a change in slip rate, there may have been a change in the style of unroofing, specifically caused by the transfer of displacement from low-angle detachment faulting to high-angle normal faults. Apatite fission-track (AFT), and apatite and zircon (U-Th)/He (AHe and ZHe) analyses were applied to samples from the Santa Catalina-Rincon (n=8 AHe, and n=9 ZHe) and Harcuvar (n=12 AFT, n=16 AHe, and n=17 ZHe) metamorphic core complexes in an attempt to resolve the possible thermal effects of high-angle normal faulting on core complex formation. Samples from the Harcuvars were taken along a transect parallel to slip direction with some samples specifically targeting high-angle normal fault locations. The AFT data collected here has the advantage of improved analysis and modeling techniques. Also, more than an order of magnitude more data were collected and analyzed than any previous studies within the Harcuvars. The AFT ages include a trend from ~22 Ma in the southwest to ~14 Ma in the northeast and provide a traditional slip rate of 7.1 mm/yr, similar to previous work. However, two major high-angle, detachment-parallel normal faults were identified, and hanging-wall samples are ~3 m.y. older than the footwalls, indicating high-angle normal faults rearranged the surface expression of the distribution of thermochronometer ages to some extent. AHe ages range from 8.1 Ma to 18.4 Ma but in general decrease with increasing distance in the slip direction. ZHe ages generally range between 13.6 Ma and 17.4 Ma. A series of unexpectedly young AFT ages (10-11 Ma), given by three complete samples and distinct population modes in others, suggest that some parts of the range underwent a later-stage unroofing event possibly caused by high-angle faulting. Confined fission-track length distributions were measured for Harcuvar samples and modeled using the modeling software HeFTy to infer thermal histories and calculate local cooling rates. These imply a component of steady cooling in some parts of the range, evidence of a different departure from a single-detachment dominated model.

Return to top | Return to Index


MICROBIAL RESPONSES TO CO2 DURING CARBON SEQUESTRATION : INSIGHTS INTO AN UNEXPLORED EXTREME ENVIRONMENT

Eugenio Felipe Unson Santillan, Ph.D.

University of Texas at Austin, May 2014

Supervisor: Philip C. Bennett

195 pages, 157 references, 9 tables

When CO2 is sequestered into deep saline aquifers, significant changes to the biogeochemistry of the system are inevitable and will affect native microbial populations both directly and indirectly. These communities are important as they catalyze many geochemical reactions in these reservoirs. We present evidence that the injection of CO2 will cause a large scale disturbance to subsurface microbial populations which will ultimately affect the solution and mineral trapping of CO2 as well as the movement of CO2 charged water through the subsurface.

Representative subsurface microorganisms including a Gram negative bacterium (G-), two Gram positive bacteria (G+), and an archaeon were tested for CO2 survival at pressures up to 50 bar and exposure times up to 24 hours. CO2 tolerance varied but shows effects on microbes is more complex than just decreasing pH and is not significantly dependent on cell wall structure. Imaging reveals that CO2 disrupts the cytoplasm possibly from changes to intracellular pH. The geochemical effect of CO2 stress is a decrease in metabolic activity such as Fe reduction and methanogenesis.

Subsurface microbial populations interact with the surrounding reservoir minerals which likely influence their ability to survive under CO2 stress. When the G- organism was grown in the presence of a mineral substrate, survival depended on the mineral type. Quartz sandstone provided a good substrate for survival while kaolinite provided a poor substrate for survival. Biofilms on quartz sandstone were rich in extracellular polymeric substances (EPS) that likely act as a barrier to slow the penetration of CO2 into the cell. The release of toxic metals from mineral dissolution at high PCO2 enhanced cell death.

To understand the long term effects of CO2 on microbial communities, water samples were taken from CO2 springs in the western United States and compared to unaffected springs. Community 16S rRNA sequence data suggests that CO2 exposed environments exhibit lower microbial diversity, suggesting environmentally stressed communities. However, differences among diversity in the springs surveyed also indicates other environmental factors that affect diversity beyond CO2. Furthermore, the isolation of a novel fermentative Lactobacillus strain from a CO2 spring, indicates viable microbial communities can exist at high PCO2.

Return to top | Return to Index


CHARACTERIZING THE SUBGLACIAL HYDROLOGY OF THWAITES GLACIER, WEST ANTARCTICA USING AIRBORNE RADAR SOUNDING

Dustin Matthew Schroeder, Ph.D.

University of Texas at Austin, May 2014

Supervisor: Donald D. Blankenship

104 pages, 118 references, 1 table

Hydrologic, lithologic, and geothermal basal boundary conditions can exert strong, even dominating, control on the evolution, stability, and sea level contribution of ice sheets and glaciers. However, the scales at which the physical processes and observable signatures of this control occur are typically smaller than the spatial resolutions currently achievable using ice penetrating radar. Further, the strength of radar bed echo returns is affected by the material and geometric properties of the bed as well as englacial attenuation from unknown ice temperature and chemistry, making assessment of basal conditions from echo strengths difficult.

To address these challenges in interpreting basal properties at glaciologically relevant scales, a new algorithmic approach is applied to measuring the radar scattering function of the bed in terms of the relative contribution of angularly narrow specular energy and isotropically scattered diffuse energy. This relative specularity content is insensitive to englacial attenuation and can be used to constrain the geometry of the bed down to the centimeter scale.

This approach is applied to an airborne radar sounding survey of Thwaites Glacier, West Antarctica using the information in the along-track scattering function to assess the extent and geometry of water across the catchment and detect the transition of that water from distributed canals to concentrated channels. This information is also used to constrain the morphology of subglacial bedforms and infer that the distribution of deformable sediments and exposed bedrock is similar to deglaciated paleo ice streams that experienced meltwater intensive retreats. Finally, models of radar echo strength and subglacial water routing are compared to estimate a catchment-wide distribution of geothermal flux consistent with rift-associated magma migration and volcanism. These observations of basal conditions provide new context for the past, current, and future evolution of Thwaites Glacier, the West Antarctic Ice Sheet, and their contribution to global sea level.

Return to top | Return to Index


THE KINEMATICS OF DISTRIBUTARY CHANNELS ON THE WAX LAKE DELTA, COASTAL LOUISIANA, USA

John Burnham Shaw, Ph.D.

University of Texas at Austin, May 2013

Supervisor: David Mohrig

170 pages, 160 references, 8 tables

The Wax Lake Delta (WLD) is a sandy, modern river delta prograding rapidly into Atchafalaya Bay. This dissertation uses field data to improve the understanding of channel kinematics that dictate river delta geometry and stratigraphy, while providing a framework for coastal restoration efforts. The studies presented here show that the distributary channel network of the WLD is erosional. In the first study, analyses of the feeder channel to the WLD and the channel network within the sub-aerially emergent delta show that the channel bed has incised into the consolidated muds that act as bedrock. The large (>62%) fraction of bedrock exposure found in multi-beam surveys is related to the under-saturation of suspended sand measured during the flood of 2009. The second study concerns the delta front beyond the emergent delta Distributary channels extend 2 – 6 km into the delta front. Four bathymetric surveys of one bifurcating distributary channel – Gadwall Pass – show that the majority of bed aggradation occurs during floods, but significant channel extension of each bifurcate channel occurs during low river discharge. In the third study, field measurements of fluid flow during a tidal cycle indicate that tidal augmentation of during periods of low river discharge is responsible for channel extension during low river discharges. Flow direction measured from streaklines present in aerial photomosaics is combined with bathymetric evolution data to quantify spatial velocity changes on the delta front. These data show that flow spreading is insufficient to prevent acceleration at channel margins, providing an explanation for observed erosion. Flow divergence is limited on the delta front by the proximity of neighboring channels, even though they are separated by 10-30 channel widths. The associated convergence of flow in inter-distributary bays occurs along “drainage troughs”. These channel-forms collect flow that has been dispensed from distributary channel network. Finally, ambient currents in Atchafalaya Bay (0.06 – 0.2 m s-1) caused by tides and the proximity to the neighboring Atchafalaya Delta appear to alter flow patterns on the delta foreset, and are responsible for channel curvature on the delta front.

Return to top | Return to Index


SIMULATING AND QUANTIFYING LAND-SURFACE BIOGEOCHEMICAL, HYDROLOGICAL, AND BIOGEOPHYSICAL PROCESSES USING THE COMMUNITY LAND MODEL VERSION 4

Mingjie Shi, Ph.D.

University of Texas at Austin, August 2013

Supervisor: Zong-Liang Yang

161 pages, 104 references, 10 tables

Carbon and nitrogen cycles, the energy cycle, and the hydrological cycle interact with each other; all are crucial to atmosphere-land studies. Carbon and nitrogen cycle from the atmosphere to vegetation communities and soil micro-organisms through their transformation in inorganic and organic pools. Ecosystem equilibrium, which is usually disturbed by extreme events (e.g., fires or drought), depends on the speeds of carbon and nitrogen uptake and decomposition. Terrestrial biogeochemistry models typically require hundreds to thousands of years for carbon and nitrogen in various pools to reach steady-state solutions, which are generally a function of soil temperature and soil water. Hydrological processes such as the root transpiration/water removal and the cold-region infiltration with the soil ice freeze/thaw status involved affect soil water content and soil temperature, and regulate carbon- and nitrogen-stock variations. Last but not least, mineral dust, a type of atmospheric aerosol, alters surface radiation/energy balance, and may act as cloud condensation nuclei to modify precipitation rates and eventually the hydrological cycle.

Therefore, we were motivated to investigate these processes in different ecosystems. Specifically, this research aims to 1) to elucidate the carbon- and nitrogen-pool adjustment processes in different ecosystems, 2) to evaluate how the root transpiration process affects ecosystem carbon exchange patterns in Amazonia, 3) to analyze the influence of soil impermeability, which is affected by the landscape freeze/thaw status in cold regions, on hydrological cycles at high latitudes, and 4) to explore the effects of surface vegetation distribution and model resolution on surface dust emissions. The Community Land Model version 4 (CLM4) was used in this study. We did numerical experiments in three environments: forest and grassland ecosystems, river basins in cold regions, and the Arabian Peninsula. Our main scientific findings are: 1) the adjustment time of the biogeochemistry components in CLM4 is longer for boreal forests than for other ecosystems, 2) with more water is lifted from deep soil, Amazonia ecosystems start to take up carbon during dry seasons, 3) the timing of boreal spring runoff simulations is improved by reducing the impermeable area underneath the snowpack, and 4) model-simulated dust emissions increase with model resolution as a result of the heterogeneities of vegetation cover and wind speed.

Return to top | Return to Index


CONTRACTIONAL AND EXTENSIONAL EVOLUTION OF AEGEAN METAMORPHIC CORE COMPLEXES, ANDROS AND TINOS ISLANDS, GREECE

Timothy Andrew Shin, M.S. Geo. Sci.

University of Texas at Austin, May 2014

Supervisors: Daniel F. Stockli and Elizabeth J. Catlos

362 pages, 209 references, 25 tables

The Aegean is a classic setting for studying exhumation of high-pressure (HP) metamorphic rocks. Two end-member models are proposed to explain the uplift of these rocks: core-complex style extension along low-angle normal faults and extrusion-wedge uplift. Extrusion-wedge underplating is the mechanism that exhumed HP rocks on Evia whereas Tinos hosts several detachments varying in age from 30-9 Ma. Andros, situated between them, may be the geological manifestation of the interplay of these processes and provides an opportunity to test these models. Detachments on NW Tinos and on Andros and the enigmatic low-angle Makrotantalon Unit contact on Andros were insufficiently dated prior to this study. Geo- and thermochronometrycombined with structural observations from sampling transects in the transport direction from (1) lower plate Cycladic Blueschist Unit on Andros and Tinos, (2) middle plate Makrotantalon Unit on Andros, and (3) hanging wall Upper Unit address these issues.

Maximum depositional ages from detrital zircon U-Pb geochronometry and structures reveal Paleocene-Eocene syn-HP metamorphism thrusting resulted in an inversed-age relationship between the Permian Makrotantalon Unit and the underlying Triassic-Eocene Cycladic Blueschist Unit on Andros. The Makrotantalon Unit has an internal inversed stratigraphy whereas the Cycladic Blueschist Unit on Andros and Tinos appear stratigraphically intact. Structures and zircon and apatite (U-Th)/He ages in transects from NW Tinos (-12-8 Ma) and central Andros Cycladic Blueschist Unit (-13-7 Ma) indicate rapid cooling due to exhumation associated with the Livada Detachment. Older cooling ages (-16-10 Ma) and structures in the Makrotantalon Unit indicate later brittle strain localization on the Makrotantalon Thrust contact is accommodated by rheologically weaker serpentinites and calc-schists, resulting in slivering of the footwall under the Livada Detachment on Andros.

Estimated mean cooling slip rates of the Livada Detachment on Andros of-3.8 (+1.2/-1.3) km Myr-1 and 2.1 (+0.2/-0.2) km Myr-1 on NW Tinos resulted in minimum vertical exhumations of 15 km and 4 km, respectively. The NCOS here accommodated -12-25% of 60 km of HP-rock exhumation from -30-7 Ma. We present a tectonic model to elucidate the evolution of the Makrotantalon Unit and the magnitude, temporal, and spatial variability of exhumation via detachments on these islands.

Return to top | Return to Index


FINANCIAL MODELING OF CONSUMER DISCOUNT RATE IN RESIDENTIAL SOLAR PHOTOVOLTAIC PURCHASING DECISIONS

Benjamin O'Gorman Sigrin, M.A., MPAff.

University of Texas at Austin, May 2013

Supervisors: Varun Rai and Jay Zarnikau

66 pages, 79 references, 13 tables

Diffusion of microgeneration technologies, particularly rooftop photovoltaic (PV), represents a key option in reducing emissions in the residential sector. This thesis uses a uniquely rich dataset from the burgeoning residential PV market in Texas to study the nature of the consumer's decision-making process in the adoption of these technologies. Focusing on the financial metrics and the information decision makers use to base their decisions upon, I study how the leasing and buying models affect individual choices and, thereby, the adoption of capital-intensive energy technologies.

Overall, the leasing model is found to more effectively address consumers' informational requirements. Contrary to previous studies, buyers and lessees of PV are not found to substantially differ along socio-demographic variables, though they do differ significantly along cash availability, levels of environmental concern, and relative importance of financial aspects. Instead, the leasing model has opened up the residential PV market to a new, and potentially very large, consumer segment—those with a tight cash flow situation.

Return to top | Return to Index


FAULT AND FRACTURE SYSTEMS RELATED TO REACTIVATION OF PRE-EXISTING STRUCTURAL ELEMENTS, DEVILS RIVER UPLIFT AND MAVERICK BASIN, TEXAS

Gordon Allen Smith Jr., M. S. Geo. Sci.

University of Texas at Austin, Month Year

Supervisor: December 2013

178 pages, 138 references, 3 tables

Pre-existing structural elements can have substantial effects on fracture and fault development in younger strata, especially in areas that undergo significant changes in tectonic setting due to reactivation along older structures. This may affect reservoir permeability, yet remain difficult to detect in subsurface data. The focus of this study centers on two styles of pre-existing structures—Paleozoic thrust belts and Late Triassic rift faults in the Devils River Uplift and Maverick Basin, respectively—which affect the development of faults and fractures in Cretaceous strata. Fault and fracture data were characterized in both the outcrop and within a 3D seismic volume. Furthermore, the role of mechanical stratigraphy on fault and fracture style in both localities was examined.

The Pecos River Canyon overlies the Paleozoic Ouachita fold-thrust belt with associated EW and SE-NW trending structures. At the surface, faults are expressed in two predominant orientations (N38E and N70E), which may be predictable angles if the pre-existing structures are reactivated by left lateral oblique slip. Detailed investigation of the fracture development related to these faults was conducted in a dry side canyon along the Pecos River. Mechanical layers were identified and mapped in outcrop to highlight fracture intensity variations between the different layers. The porosity and/or the degree of dolomitization are identified as controls on fracture development, with the lowest strength layer and least fractured being highly dolomitized with the largest porosity of any observed layer in outcrop.

Southeast of Lewis Canyon, a 3D seismic of the Maverick Basin reveals linear discontinuities, interpreted as low-offset faults, within the Cretaceous Glen Rose through Austin Chalk that appear similar to those observed in outcrop along the Lower Pecos River. These faults are shown to have an increase in intensity within strata above older Late Triassic-age rift faults. It is proposed that the small faults form during reactivation of the rift faults and exhibit differential degrees of intensity and vertical terminations against six identified mechanical boundaries observed within the 3D seismic volume.

Return to top | Return to Index


ON THE SPIRAL TROUGHS OF MARS

Isaac Blaine Smith, Ph.D. Geological Sciences

University of Texas at Austin, August 2013

Supervisor: John W. Holt

168 pages, 131 references, 3 tables

The north and south polar layered deposits (NPLD and SPLD respectively) of Mars are 2 - 3 km thick and mostly ice, comprising nearly all of the known water reserves on Mars. They are commonly believed to hold a detailed record of recent (~ 10 - 100 Myr) climate within their layers. Dominating the surface of the NPLD, intriguing spiral depressions called troughs, exhibit a pinwheel appearance.

In late 2006, the Shallow Radar (SHARAD) instrument began making observations. SHARAD can detect internal structure within the PLD, making observations that are impossible with instruments that only inspect the surface. SHARAD data reveals a unique stratigraphic record associated with trough formation and migration. The troughs did not exist during deposition of the first half of NPLD accumulation but initiated some 1000 m below the current surface and have migrated as much as 100 km northward. Three processes are responsible for this migration: wind transport, insolation induced sublimation, and atmospheric deposition.

I synthesize work from ground penetrating radar, optical imagery, established analogs, and atmospheric modeling in order to derive a process model that describes trough formation and evolution, including migration. The NPLD spiral troughs belong to a larger classification of features called cyclic steps, which can exist in either erosional or depositional environments. On the SPLD, troughs and a variety of other features exist. While SPLD features are more complex than NPLD troughs, they exist due to the same three processes.

Return to top | Return to Index


GEOCHEMISTRY AND GEOCHRONOLOGY OF THE BEYPAZARI GRANITOID PLUTON (NORTH CENTRAL TURKEY): TECTONIC IMPLICATIONS

Pamela Ann Speciale, Bachelor of Science

University of Texas at Austin, May 2013

Supervisor: Elizabeth Catlos

82 pages, 83 references, 8 tables

The Beypazari granitoid was emplaced in a Late Cretaceous volcanic arc in north central Turkey. This pluton crops out north of a major tectonic suture and provides important evidence for processes that occurred during the closure of the Neo-Tethys Ocean. A generally accepted tectonic model for emplacement is northward subduction of Neo-Tethyan oceanic lithosphere beneath Laurasia. This study presents new geochemical and geochronological analyses of the pluton, including the first U-Pb zircon ages and the first cathodoluminescence (CL) images used to interpret ages from the Beypazari granitoid. Analyses reveal a geochemically heterogeneous granitoid, with mafic enclaves and aplite dikes. Zircons from its northern granodiorite and quartz monzonite exposure dated in rock thin section are 95.4±4.2 Ma to 51.5±2.2 Ma (238U/206Pb, ±lσ) and display characteristic igneous zoning in CL. Its oldest Late Cretaceous ages likely time crystallization, but inspection of younger Paleocene and Eocene grains in composite CL-secondary electron images show they are located along grain boundaries surrounded by alteration textures and were affected by fluid-driven metamorphism. Ages between the extremes were often obtained from zircon mid-rims and likely time continuous crystallization until -70 Ma. Zircons from an aplite dike are Paleocene to Pliocene. In CL, its two youngest zircons (5.6±0.3 Ma and 5.0±0.3 Ma) show evidence of fluid alteration and recrystallization, but could possibly time a transition in the region to extrusional tectonics. The Beypazari zircon ages overlap with those from the Sivrihisar granitoid located ~70 km south, suggesting they share parts of a common tectonomagmatic history. This study presents a model for their development wherein subduction and break off of two major slabs induce asthenospheric melts and are the cause of protracted zircon crystallization. Evidence for these processes is revealed in recent teleseismic mantle tomography studies showing fast seismic anomalies below the 660 km discontinuity beneath the Sakarya, Tavsanli and Afyon zones, and interpreted as possible remnants of detached slab(s) or delaminated lithosphere.

Return to top | Return to Index


AN EFFICIENT ALGORITHM FOR TWO-POINT SEISMIC RAY TRACING IN LAYERED MEDIA

Yanadet Sripanich, Bachelor of Science

University of Texas at Austin, May 2013

Supervisor: Sergey B. Fomel

56 pages, 27 references, 8 tables

I propose an efficient algorithm for two-point seismic ray tracing in layered media by means of the bending method based on Fermat's principle of stationary traveltime. The algorithm uses the fact that the matrix of the second derivatives of traveltime function with respect to the points of intersection at the interfaces has a blocked tridiagonal structure. This feature allows me to easily invert the matrix via a series of recursive steps, which leads to a fast implementation of the Newton-Raphson method to efficiently solve for a raypath with stationary traveltime. To demonstrate accuracy of the proposed algorithm, I compare results computed from the algorithm to those from analytical solutions. I conduct Kirchhoff modeling in layered medium as an example of possible applications of the developed algorithm.

Return to top | Return to Index


CONTEXTUALIZING VERTEBRATE FAUNAL DYNAMICS : NEW PERSPECTIVES FROM THE TRIASSIC AND EOCENE OF WESTERN NORTH AMERICA

Michelle Renae Stocker, Ph.D.

University of Texas at Austin, May 2013

Supervisor: Christopher J. Bell

297 pages, 375 references

Conceptualizations of actual biological patterns as preserved in the fossil record must accommodate the results of biotic and abiotic drivers of faunal dynamics. However, those conceptualizations also may reflect cognitive biases resulting from foundational philosophical stances. Whether fossils are conceptualized as the remains of biological entities or as geological objects will affect both taxonomic identifications and secondary inferences derived from those identifications. In addition, operational research bias centered on relativistic views of ‘importance’ of particular components (i.e., taxonomic or skeletal region) of the assemblage results in preferential documentation of some taxa and marginalization of others. I explored the consequences of those specific cognitive and operational biases through examination of Triassic and Eocene faunal assemblages in western North America. For the Triassic I focused on taxonomic and systematic treatments of Paleorhinus, a group of phytosaurs important for the establishment of biochronologic correlations. Specimen-level reexamination of Paleorhinus supported a restricted usage of Paleorhinus as a clade, dissolved a biochronologic connection between terrestrial and marine deposits, and indicated a prior compression of the early part of the Late Triassic as a result of previous conceptualizations of species. I reexamined the Otis Chalk tetrapod assemblage in light of new specimens and modern phylogenetic frameworks. My examination supported a restricted usage of the Otischalkian for biochronologic correlation of the Late Triassic, and emphasized the importance of apomorphic character-based specimen examinations in conjunction with detailed lithostratigraphy prior to the development of biochronologic schema. For the Eocene I focused on undocumented terrestrial reptiles from the late Uintan fauna of West Texas. Specifically I discovered new taxa and new geographic occurrences of amphisbaenians and caimanine crocodylians. The amphisbaenians represent the southernmost record of the clade in the North American Paleogene, and, when combined with other amphisbaenian records, document that the clade responded to late Paleogene climatic changes in ways different from the inferred mammalian response. The new taxon of caimanine crocodylian represents a new geographic and temporal record of that clade. That new record indicates that the biogeographic range of extant caimans represents a climate-driven restriction from a formerly more expansive range, and suggests that the previous geographic and temporal gap in paleodistribution data is related to sampling biases and is not a solely a biological phenomenon. These data indicate that reliable characterization of vertebrate faunal dynamics requires open acknowledgment and appropriate documentation of cognitive and operational biases that affect interpretations of paleontological data.

Return to top | Return to Index


ROLE OF MESOPHYLL CO2 DIFFUSION AND LARGE-SCALE DISTURBANCES IN THE INTERACTIONS BETWEEN CLIMATE AND CARBON CYCLES

Ying Sun, Ph.D.

University of Texas at Austin, May 2013

Supervisor: Robert E. Dickinson

185 pages, 215 references, 6 tables

Reliable prediction of climate change and its impact on and feedbacks from terrestrial carbon cycles requires realistic representation of physiological and ecological processes in coupled climate-carbon models. This is hampered by various deficiencies in model structures and parameters. The goal of my study is to improve model realism by incorporating latest advances of fundamental eco-physiological processes and further to use such improved models to investigate climate-carbon interactions at regional to global scales. I focus on the CO2 diffusion within leaves (a key plant physiological process) and large-scale disturbances (a fundamental ecological process) as extremely important but not yet in current models.

The CO2 diffusion within plant leaves is characterized by mesophyll conductance (gm), which strongly influences photosynthesis. I developed a gm model by synthesizing new advances in plant-physiological studies and incorporated this model into the Community Land Model (CLM), a state-of-art climate-carbon model. I updated associated photosynthetic parameters based on a large dataset of leaf gas exchange measurements. Major findings are: (1) omission of gm underestimates the maximum carboxylation rate and distorts its relationships with other parameters, leading to an incomplete understanding of leaf-level photosynthesis machinery; (2) proper representation of gm is necessary for climate-carbon models to realistically predict carbon fluxes and their responsiveness to CO2 fertilization; (3) fine tuning of parameters may compensate for model structural errors in contemporary simulations but introduce large biases in future predictions. Further, I have corrected a numerical deficiency of CLM in its calculation of carbon/water fluxes, which otherwise can bias model simulations.

Large-scale disturbances of terrestrial ecosystems strongly affect their carbon sink strength. To provide insights for modeling these processes, I used satellite products to examine the temporal-spatial patterns of greenness after a massive ice storm. I found that the greenness of impacted vegetation recovered rapidly, especially in lightly and severely impacted regions. The slowest rebound occurred over moderately impacted areas. This nonlinear pattern was caused by an integrated effect of natural regrowth and human interventions.

My results demonstrate mechanisms by which terrestrial carbon sinks could be significantly affected and help determine how these sinks will behave and so affect future climate.

Return to top | Return to Index


CINDER POOL'S SULFUR CHEMISTRY : IMPLICATIONS FOR THE ORIGIN OF LIFE IN HYDROTHERMAL ENVIRONMENTS

Lindsey A. Sydow, M.S. Geo. Sci.

University of Texas at Austin, August 2013

Supervisor: Philip C. Bennett

103 pages, 40 references, 13 tables

One chemoautotrophic origin of life theory posits the abiotic formation of alkyl thiols as an initial step to forming biomolecules and eventually a simple chemoautotrophic cell. The premise of this theory is that a recurring reaction on the charged surfaces of pyrite served as a primordial metabolism analogous to the reductive acetyl-CoA pathway (Wächtershäuser 1988) that was later enveloped by a primitive cellular membrane. Alkyl thiols have not previously been identified in terrestrial hot springs as unequivocally abiogenic, but they have been produced in the laboratory under hydrothermal conditions in the presence of a catalyst.

I analyzed the dissolved gas content of several hot springs and conducted sterile laboratory experiments in order to evaluate the abiogenic formation of methanethiol (CH3SH), the simplest of the alkyl thiols. Specifically of interest was Cinder Pool, an acid-sulfate-chloride hot spring in Yellowstone National Park. This spring is unusual in that it contains a subaqueous molten sulfur layer (~18 m depth) and thousands of iron-sulfur-spherules floating on the surface, which are created by gas bubbling through the molten floor of the spring. This material could potentially serve as a reactive and catalytic surface for abiogenic CH3SH formation in Cinder Pool.

Gas samples were collected from Cinder Pool and an adjacent hydrothermal feature in fall of 2011 using the bubble strip method. Two samples contained measurable quantities of CH3SH and other organic sulfur gases, with concentrations of all gases generally higher at the bottom of the pool. Laboratory microcosm experiments were conducted to replicate these findings in a sterile environment. Analog Cinder Pool water was injected into serum bottles containing different iron-sulfur compounds, including cinders collected from the pool itself, as catalytic surfaces for the CH3SH generating reaction. The bottles were then charged with hydrogen (H2), carbon dioxide (CO2), and carbon disulfide (CS2) as reaction gases and incubated for a week at temperatures between 60 and 100°C. Bottles used either powdered FeS, FeS2 (pyrite) or cinder material as a catalytic surface, and all of these surfaces were capable of catalyzing CH3SH formation. In bottles without imposed CS2, however, cinder material was the only surface that produced any detectable CH3SH.

While CH3SH is central to the autotroph-first theory and has been synthesized in the laboratory (e.g. Heinen and Lauwers 1996), it has not previously been observed to form abiotically in natural systems. I have identified CH3SH in a natural hydrothermal feature where it is unlikely to have formed secondary to microbial activity, and I have duplicated these field findings in sterile laboratory experiments using the cinders as a reactive surface for formation.

Return to top | Return to Index


HIDDEN INTRUSIONS AND MOLYBDENITE MINERALIZATION BENEATH THE KUCING LIAR SKARN, ERTSBERG-GRASBERG MINING DISTRICT, PAPUA, INDONESIA

Marin Cherise Trautman, M.S. Geo. Sci.

University of Texas at Austin, August 2013

Supervisor: Mark Cloos

336 pages, 70 references, 12 tables

The Ertsberg-Grasberg Mining District of Papua, Indonesia (Western New Guinea) hosts the Ertsberg Cu-Au Skarn, the giant Grasberg Porphyry Cu-Au deposit, and several other orebodies. Two 1700-meter-long cores beneath the Kucing Liar ore skarn (KL98-10-22) and the Grasberg Igneous Complex (KL98-10-21) contain high concentrations of vein and disseminated molybdenite. KL98-10-22, the focus of this study, intersects two previously unencountered intrusions, the “Tertiary intrusion Kucing Liar” (Tikl) and “Tertiary Pliocene intrusion” (Tpi). An intense dilatational quartz vein stockwork cuts Tikl and Ekmai Sandstone (Kkes) units, predating Tpi intrusion. Prior to these ultradeep cores, which extend almost 3 km below pre-mining surface, molybdenite was rarely observed in the district.

Geochemistry and isotopic data indicate that Tikl and Tpi intrusions originated from the same large magmatic system that emplaced other ore-forming Ertsberg-Grasberg district intrusions. Magma in a lower crustal chamber was recharged at least twice, according to Sr-Nd data. Laser-ablation inductively-coupled plasma mass spectrometry of magmatic zircons yields 238U-206Pb ages between 3.40 ± 0.12 Ma (Dalam Andesite) and 2.77 ± 0.15 Ma (Ertsberg intrusion), revealing a shorter period of igneous activity than previously measured by K-Ar and Ar-Ar dating. Analyses include composite ages of 3.28 ± 0.08 Ma for Tikl and 3.18 ± 0.11 Ma for Tpi. Inherited zircon cores indicate Precambrian (mostly Proterozoic) basement.

Molybdenite veining beneath the Kucing Liar Skarn and Grasberg Igneous Complex postdates stockwork veining and occurred before the 2.99 ± 0.11 Ma Kali dikes. Only one molybdenite vein was observed cutting Tpi. Molybdenites yielded ~3 Ma Re-Os ages and anomalous ›4 Ma and ‹0.5 Ma ages; anomalous ages were not reproducible in follow-up analyses (this study). Smearing deformation of molybdenite (through fault activity) causes crystal strain, likely leading to annealing recrystallization. Recrystallization possibly redistributes daughter-product Os, resulting in anomalous ages from annealed material. Fluids with high Mo/Cu ratios (which were likely supercritical) precipitated late-stage molybdenite deep in the system. These fluids developed through magma chamber crystallization, which concentrated molybdenum in the melt as an incompatible element, and stripping of Cu from the magma chamber during hydrothermal activity.

Return to top | Return to Index


FACIES VARIABILITY IN DEEP WATER CHANNEL-TO-LOBE TRANSITION ZONE : JURASSIC LOS MOLLES FORMATION, NEUQUEN BASIN ARGENTINA

Eugen Petrut Tudor, MS Geo Sci

University of Texas at Austin, May 2014

Supervisors: Ron Steel and Cornel Olariu

91 pages, 75 references, 2 tables

This study focuses on the facies changes from the lower slope to toe-of-slope to basin floor over a 10 km outcrop belt, in down-dip and oblique-strike directions to the basin margin. The Jurassic Los Molles Formation in Neuquen Basin, Argentina represents the slope and basin floor of basin margin clinoforms, coeval with the shallow water and fluvial deposits named Las Lajas and Challaco formations respectively. The shallow and deep water deposits are diachronously linked in an Early-Mid Jurassic source-to-sink system developed in a back-arc basin during the incipient development of the Andes Mountains. Satellite images, high resolution panorama pictures and measured sections were used to correlate and interpret the spatial variability and overall geometry of the base of slope to basin floor units. The observations of this study refine the model for the channel-to-lobe transition zone with increase recognition and quantification of facies and architecture variability. The Los Molles basin margin was coarse grained and was ideal to observe changes in the geometry and depositional facies of channel-to-lobe deposits from updip to downdip continuous over an 8 km outcrop belt. The described channel-to-lobe transition zone clearly shows a downdip change in bed boundaries from dominantly erosive to non-erosional (bypass) to depositional and with a range of distinct facies changes. In the transition zone the sand to shale ratio is high (N:G: 65-70 %), with gutter casts and deep scours, with a high degree of amalgamation, gravel lags, mud rip-up clasts and laterally migrating beds. Within the same depositional unit (deep water lobe), at the base of the slope, the dominant sandstone beds change from amalgamated structureless and normal graded sandstone beds in the channelized lobe axis to parallel laminated and normally graded in the channelized lobe off-axis areas. Similar facies changes have been observed along proximal to distal direction. The lateral change of the dominant structures in the beds indicates changes in the flow regime and depositional style.

Return to top | Return to Index


SLOPE TO BASIN-FLOOR EVOLUTION OF CHANNELS TO LOBES, JURASSIC LOS MOLLES FORMATION, NEUQUÉN BASIN, ARGENTINA

Nataleigh Kristine Vann, MS Geo Sci

University of Texas at Austin, December 2013

Supervisors: Ronald J. Steel and Cornel Olariu

95 pages, 36 references, 1 table

The relatively steep and short-headed Neuquén Basin margin provides an excellent laboratory for demonstrating down slope changes in sediment gravity flow bed thickness, grain size and facies, as well as channel to lobe transitions. Approximately 400m high clinoformal, shelf-slope-basin-floor deposits of Jurassic Los Molles Formation outcrops are evaluated for reservoir scale definition of facies and architectures in the La Jardinera field area, Neuquén Basin. Slope deposits represent the accretionary front of the prograding shelf margin that were fed by a coarse grained shelf (Lajas Formation). Mapping of a high-resolution satellite images draped on digital elevation model resolved a sub-meter stratigraphic framework. Thirty-three measured sections from outcrops exposed along a 5km transect characterize the evolution of sand body architectures from the shelf edge to the basin floor. The Neuquén Basin margin is typified by four main depositional environments that transition from shelf edge incisions filled with conglomerates, to confined channels in upper- to middle-slope reaches, to weakly confined channels on the lower slope to sheet-like lobes and distributary channel complexes that drape onto both the lower slope and basin floor. Along the slope to basin floor profile the depositional architecture changes by overall decrease in grain size, amalgamation of beds and degree of erosion.

Confined slope channels are up to 25m deep, isolated within muddy slope deposits and have complex multistory fills marked by basal and internal erosive contacts lined with mud-clast and/or pebble conglomerates. Channel axes contain amalgamated, medium to coarse sandstones that thin and fine towards channel margins over 100m. Down dip, lower slope channels are up to 400m wide and less than 10m thick. A marked reduction in mud clasts and conglomeratic material at basal erosional surfaces in weakly confined channels represent a downslope decrease in flow energy. However, distinct meter scale erosion surfaces continue to be recognizable where thin ripple laminated sands are truncated on channel margins by amalgamated structureless sands. Erosional surfaces are absent in laterally extensive (›5km), sheet-like lobes of basin-floor fans that are generally finer grained than lower or upper slope channel fills. There are lenticular debrites and thin micro-conglomerates associated with basin-floor fans.

Return to top | Return to Index


DECISION SUPPORT MODELING FOR PROJECT SELECTION IN TEXAS WATER PLANNING

Elizabeth Leslie Waite, M.S.E.E.R.

University of Texas at Austin, December 2013

Supervisors: Michael E. Webber and Suzanne A. Pierce

210 pages, 25 references, 5 tables

The state of Texas is facing critical decisions that will greatly impact the preparedness of the state to meet future water demand. Consequently, during the 83rd Texas Legislative Session, state legislators proposed House Bill 4 (HB 4), a bill that if funded will provide an additional two billion dollars of funding for Texas water planning projects. Objectively evaluating and prioritizing projects would enable the efficient distribution of funding and minimize conflicts between water users. This project uses multi-criteria decision modeling to compare various evaluation criteria and decision preferences and prioritize proposed water management strategies in the 2012 State Water Plan. Combinations of project, regional, and legislative criteria are considered in eight decision scenarios. Projects are evaluated using Logical Decisions software and Microsoft Excel to calculate project utility and identify distribution strategies for funding. Results of this study provide insight into regional and strategy funding biases. Additionally, the decision model analyses highlight the effects of project prioritization on urban vs. rural and arid vs. humid Texas water conflicts.

Return to top | Return to Index


THE EASTERN BOX TURTLE (TERRAPENE CAROLINA) IN SPACE AND TIME

Natasha Slonim Vitek, M.S.

University of Texas at Austin, May 2013

Supervisor: Christopher J. Bell

156 pages, 95 references, 16 tables

Variation is a key component of the evolutionary process. However, variation often is poorly understood within species. The eastern box turtle (Terrapene carolina) presents an excellent opportunity to study that topic because extant populations have high levels of variation in soft-tissue characters as well as morphological variation in skeletal characters. To explore patterns of spatiotemporal variation, I used geometric morphometrics to quantify shape within three datasets. First, I asked to what extent size explained total shape variation using an ontogenetic series of 101 specimens. Next, I examined to what extent subspecies were morphologically distinct and identifiable in the modern record, and to what degree they explained overall variation using a dataset of 200 modern specimens. Finally, I compared the patterns in the modern biota to those from the fossil record using the previous datasets as well as a fossil dataset of 44 Pleistocene shells of T. carolina.

I found that in four views of the turtle shell (dorsal, ventral, posterior, and lateral), size significantly explains 10% - 31% of the variation in shape. Some of the characters correlated with size were historically ascribed to characters of subspecies. Studying the extent to which size explains overall variation in different subsamples of my data allowed me to discover a new way of classifying segments of a population in order to account for size in future studies. Subspecies identification also explained a statistically significant amount of overall shape variation. However, the results of assignments tests and CVAs indicated insignificant or unreliable differences. Results indicate that differences between putative subspecies are more statistically significant than they are biologically significant. They do not support the recognition of subspecies in T. carolina. The inability of statistical analyses to identify individuals of a subspecies based on shell shape means that subspecies cannot be identified in the fossil record. Some of the same relationships between shape and size are present in the fossil record and the modern biota, but other morphological patterns are unique to fossil specimens. Two of the morphotypes co-occur in the same strata, and represent a unique evolutionary pattern not seen in the modern biota.

Return to top | Return to Index


USE OF 3-DIMENSIONAL DYNAMIC MODELING OF CO2 INJECTION FOR COMPARISON TO REGIONAL STATIC CAPACITY ASSESSMENTS OF MIOCENE SANDSTONE RESERVOIRS IN THE TEXAS STATE WATERS, GULF OF MEXICO

Kerstan Josef Wallace, M.S.Geo.Sci.

University of Texas at Austin, May 2013

Supervisors: Timothy A. Meckel and Michael H. Young

137 pages, 75 references, 4 tables

Geologic sequestration has been suggested as a viable method for greenhouse gas emission reduction. Regional studies of CO2 storage capacity are used to estimate available storage, yet little work has been done to tie site specific results to regional estimates. In this study, a 9,258,880 acre (37469.4 km2) area of the coastal and offshore Texas Miocene interval is evaluated for CO2 storage capacity using a static volumetric approach, which is essentially a discounted a pore volume calculation. Capacity is calculated for the Miocene interval above overpressure depth and below depths where CO2 is not supercritical. The goal of this study is to determine the effectiveness of such a regional capacity assessment, by performing refinement techniques that include simple analytical and complex reservoir injection simulations. Initial refinement of regional estimates is performed through net sand picking which is used instead of the gross thickness assumed in the standard regional calculation. The efficiency factor is recalculated to exclude net-to-gross considerations, and a net storage capacity estimate is calculated.

Initial reservoir-scale refinement is performed by simulating injection into a seismically mapped saline reservoir, near San Luis Pass. The refinement uses a simplified analytical solution that solves for pressure and fluid front evolution through time (Jain and Bryant, 2011). Porosity, permeability, and irreducible water saturation are varied to generate model runs for 6,206 samples populated using data from the Atlas of Northern Gulf of Mexico Gas and Oil Reservoirs (Seni, 2006).

As a final refinement step, a 3D dynamic model mesh is generated. Nine model cases are generated for homogeneous, statistically heterogeneous, and seismic-based heterogeneous meshes to observe the effect of various geologic parameters on injection capacity.

We observe downward revisions (decreases) in total capacity estimation with increasingly refined geologic data and scale. Results show that estimates of storage capacity can decrease significantly (by as much as 88%) for the single geologic setting investigated. Though this decrease depends on the criteria used for capacity comparison and varies within a given region, it serves to illustrate the potential overestimation of regional capacity assessments compared to estimates that include additional geologic complexity at the reservoir scale.

Return to top | Return to Index


EVALUATION OF A LAND SURFACE SOLAR RADIATION PARTITIONING SCHEME USING REMOTE SENSING AND SITE LEVEL FPAR DATASETS

Kai Wang, M.S.Geo.Sci.

University of Texas at Austin, August 2013

Supervisor: Robert E. Dickinson

56 pages, 59 references, 1 table

Land surface covers only 30% of the global surface, but contributes largely to the intricacy of the climate system by exchanging water and energy with the overlying atmosphere. The partitioning of incident solar radiation among various components at the land surface, especially vegetation and underlying soil, determines the energy absorbed by vegetation, evapotranspiration, partitioning between surface sensible and latent heat fluxes, and the energy and water exchange between the land surface and the atmosphere. Because of its significance in climate model, land surface model solar radiation partitioning scheme should be evaluated in order to ensure its accuracy in reproducing these naturally complicated processes. However, few studies evaluated this part of climate model. This study examines a land surface solar radiation partitioning scheme, i.e., that of the Community Land Model version 4 (CLM4) with coupled carbon and nitrogen cycles.

Taking advantage of multiple remote sensing fraction of absorbed photosynthetically active radiation (FPAR) datasets, ground observations and a unique 28-year FPAR dataset derived from the Global Inventory Modeling and Mapping Studies (GIMMS) Normalized Difference Vegetation Index (NDVI) dataset, we evaluated the CLM4 FPAR’s seasonal cycle, diurnal cycle, long-term trends and spatial patterns. Our findings show the model roughly agrees with observations in the seasonal cycle , long-tern trend and spatial patterns but does not reproduce the diurnal cycle. Discrepancies also exist in seasonality magnitudes, peak value months and spatial heterogeneity. We identified the discrepancy in the diurnal cycle as due to the absence of dependence on sun angle in the model. Implementation of sun angle dependence in a one-dimensional (1-D) model is proposed. The need for better relating vegetation to climate in the model indicated by long-term trends is also noted. Evaluation of the CLM4 land surface solar radiation partitioning scheme using remote sensing and site level FPAR datasets provides targets for future development in its representation of this naturally complicated process.

Return to top | Return to Index


THE USE OF δ13C VALUES OF LEPORID TEETH AS INDICATORS OF PAST VEGETATION

Travis Zhi-Rong Wicks, M.S. Geo. Sci.

University of Texas at Austin, May 2013

Supervisors: Timothy M. Shanahan and Christopher J. Bell

94 pages, 91 references, 5 tables

Records of change of δ13C values in vertebrate teeth offer an opportunity to gain insight into changes in past vegetation. Increasingly, teeth from small mammals are used for such purposes, but because their teeth grow very rapidly, seasonal changes in vegetation potentially provide a large source of variability in carbon isotope composition, complicating interpretations of small mammal tooth isotope data. To investigate the controls of seasonality on the stable isotope composition of fossil teeth, we constructed a Monte-Carlo-based model to simulate the effects of changes in the seasonal pattern of diet in leporid lagomorphs (rabbits and hares) on the distribution of δ13C values in random populations of leporid teeth from the Edwards Plateau in central Texas. Changes in mean-state, seasonal vegetation range, and relative season length manifest themselves in predictable ways in the median, standard deviation, and skewness of simulated tooth δ13C populations, provided sufficient numbers of teeth are analyzed. This Monte Carlo model was applied to the interpretation of a 20,000 year record of leporid tooth δ13C values from Hall’s Cave on the Edwards Plateau in central Texas. Variations in the δ13C values of teeth deposited at the same time (standard deviation = 1.69‰) are larger than changes in the mean vegetation composition reconstructed from bulk organic carbon δ13C, indicating the influence of short-term variability, making it difficult to assess changes in mean C3/C4 vegetation from the tooth δ13C data. However, populations of teeth from different climate intervals (e.g., the late Glacial, Younger Dryas, and the Holocene) display changes in the shape of the tooth δ13C distributions. Interpretation of these changes as shifts in seasonal vegetation patterns that are based upon results from our model are consistent with hypothesized climatic changes. An increase in the standard deviation of the tooth population between the late Glacial and the Younger Dryas – Holocene is consistent with an increase in seasonality. Furthermore, a shift to more C3-dominated vegetation in the tooth δ13C distribution during the Younger Dryas is accompanied by a more skewed population – indicative of not only wetter conditions but an increase in the duration in the C3 growing season. However, late Holocene changes in vegetation are not clear in the tooth data, despite the evidence from bulk organic carbon δ13C values for an increase in % C3 vegetation of 57%. Small mammal teeth can potentially provide unique insights into climate and vegetation on seasonal and longer timescales that complement other data, but should be interpreted with a careful consideration of local conditions, taxon ecology and physiology, and the dominant timescales of isotope variability.

Return to top | Return to Index


DELINEATING CONTROLS ON HYDROLOGIC VARIABILITY AND WATER GEOCHEMISTRY IN CENTRAL TEXAS

Corinne Wong, PhD

University of Texas at Austin, August 2013

Supervisor: Jay L. Banner

226 pages, 249 references, 21 tables

There is a strong concern about how water resources will be affected by future climate change. Investigation of how a hydrologic system might respond to climate change, however, requires a detailed understanding of the controls on and factors that might affect that system. The research presented in this dissertation focuses on improving the understanding of the Barton Springs segment of the Edwards aquifer in central Texas. The first three chapters of this dissertation present research investigating spatial and temporal controls on groundwater geochemistry. The fourth chapter focuses on characterizing and understanding the controls on long-term hydrologic variability by reconstructing past climate from a speleothem (cave mineral deposit) collected from a central Texas cave. On spatial scales, Edwards aquifer groundwater geochemistry is influenced by water-rock interaction (calcite and dolomite recrystallization, gypsum dissolution, and calcite precipitation) and mixing between fresh groundwater and saline groundwater. On temporal scales, variation in groundwater geochemistry is dictated by the extent to which fresh groundwater mixes with recharging stream water. The degree of mixing is sensitive to changes in climate conditions (i.e., more mixing under wetter conditions) and type of flow path (i.e., conduit or diffuse) that dominantly supplies a given site. The geochemistry of stream water, which provides the majority of recharge to the aquifer, is degrading over time and indirectly controlled by anthropogenic sources under both wet and dry conditions. Climate reconstructed from a speleothem suggests that central Texas moisture conditions were relatively constant from the mid to late Holocene (0 to 7 ka), except for an extended dry interval from 0.5 to 1.5 ka. Speleothem δ18O values spike during this dry interval, suggesting that decreases in Pacific-derived moisture or decreased tropical storm activity might have been coincident with the prolonged dry interval. This research has improved understanding of the natural variability of and controls on physical and geochemical components of hydrologic system in central Texas.

Return to top | Return to Index


LITHOFACIES, DEPOSITIONAL ENVIRONMENTS, AND SEQUENCE STRATIGRAPHY OF THE PENNSYLVANIAN (MORROWAN-ATOKAN) MARBLE FALLS FORMATION, CENTRAL TEXAS

Stephanie Grace Wood, M.S. Geo. Sci.

University of Texas at Austin, August 2013

Supervisors: Stephen C. Ruppel and Robert G. Loucks

259 pages, 189 references, 9 tables

The Pennsylvanian Marble Falls Formation in the Llano Uplift region of the southern Fort Worth Basin (Central Texas) is a Morrowan-Atokan mixed carbonate-siliciclastic unit whose deposition was influenced by icehouse glacioeustatic sea-level fluctuations and foreland basin tectonics. Previous interpretations of the Marble Falls Formation focused on outcrop data at the fringes of the Llano Uplift. This study uses a series of 21 cores to create a facies architectural model, depositional environmental interpretation, and regional sequence stratigraphic framework. On the basis of core data, the study area is interpreted to have been deposited in a ramp setting with a shallower water upper ramp area to the south and a deeper water basin setting to the north. Analysis of cores and thin sections identified 14 inner ramp to basin facies. Dominant facies are: (1) burrowed sponge spicule packstone, (2) algal grain-dominated packstone to grainstone, (3) skeletal foraminiferal wackestone, and (4) argillaceous mudstone to clay shale.

Facies stacking patterns were correlated and combined with chemostratigraphic data to improve interpretations of the unit’s depositional history and form an integrated regional model.

The Marble Falls section was deposited during Pennsylvanian icehouse times in a part of the Fort Worth Basin with active horst and graben structures developing in response to the Ouachita Orogeny. The resulting depositional cycles reflect high-frequency sea-level fluctuations and are divided into 3 sequences. Sequence 1 represents aggradational ramp deposition truncated by a major glacioeustatic sea-level fall near the Morrowan-Atokan boundary (SB1). This fall shifted accommodation basinward and previously distal areas were sites of carbonate HST in Sequence 2 deposition following a short TST phase. Sequence 3 represents the final phase of carbonate accumulation that was diachronously drowned by Smithwick siliciclastics enhanced by horst and graben faulting.

These findings contribute to our understanding of the depositional response to glacioeustatic sea-level changes during the Pennsylvanian and can also form the basis for constructing a sedimentological and facies analog for Morrowan to Atokan shallow- to deepwater carbonates in the Permian Basin and the northern Fort Worth Basin.

Return to top | Return to Index


DYNAMICS OF THE EASTERN EDGE OF THE RIO GRANDE RIFT

Yu Xia, M.S. Geo. Sci.

University of Texas at Austin, August 2013

Supervisor: Stephen P Grand

60 pages, 43 references

The Western U.S. has experienced widespread extension during the past 10’s of millions of years, largely within the Basin and Range and Rio Grande Rift provinces. Tomography results from previous studies revealed narrow fast seismic velocity anomalies in the mantle on either side of the Rio Grande Rift as well as at the western edge of the Colorado Plateau. The fast mantle anomalies have been interpreted as down-welling that is part of small scale mantle convection at the edge of extending provinces. It was also found that crust was thicker than average above the possible mantle down-welling, indicating that mantle dynamics may influence crustal flow. We present results from P/S conversion receiver functions using SIEDCAR (Seismic Investigation of Edge Driven Convection Associated with the Rio Grande Rift) data to determine crustal and lithospheric structure beneath the east flank of the Rio Grande Rift. Crustal and lithosphere thickness are estimated using P-to-S and S-to-P receiver functions respectively. Receiver function migration methods were applied to produce images of the crust and lithosphere. The results show variable crustal thickness through the region with an average thickness of 45 km. The crust achieves its maximum thickness of 60km at 105W longitude, between 33.5N and 32.2N latitude. This observation confirms previous receiver function results from Wilson, et al., 2005. Body wave tomography (Rocket, 2011; Schmandt and Humphreys, 2010) using similar data to what we used for the receiver function analysis, shows mantle downwelling closely associated with the thickened crust. We believe that the thickened crust might be due to lower crustal flow associated with mantle downwelling or mantle delamination at the edge of the Rio Grande Rift. In this model the sinking mantle pulls the crust downward causing a pressure gradient within the crust thus causing the flow. Our S-P images show signal from the lithosphere-asthenosphere boundary (LAB) with an average LAB thickness of 100 km but with a sharp transition at about 105° W from 75 km to over 100 km. The region with abnormally thick crust overlies a region where the lithosphere appears to have a break. We interpret our results as showing that lower lithosphere has and is delaminating near the edge of the Great Plains accompanied by lower crustal flow in some places determined by lower crustal viscosity.

Return to top | Return to Index


NOVEL STOCHASTIC INVERSION METHODS AND WORKFLOW FOR RESERVOIR CHARACTERIZATION AND MONITORING

Yang Xue, PhD

University of Texas at Austin, December 2013

Supervisor: Mrinal K. Sen

161 pages, 101 references

Reservoir models are generally constructed from seismic, well logs and other related datasets using inversion methods and geostatistics. It has already been recognized by the geoscientists that such a process is prone to non-uniqueness. Practical methods for estimation of uncertainty still remain elusive. In my dissertation, I propose two new methods to estimate uncertainty in reservoir models from seismic, well logs and well production data.

The first part of my research is aimed at estimating reservoir impedance models and their uncertainties from seismic data and well logs. This constitutes an inverse problem, and we recognize that multiple models can fit the measurements. A deterministic inversion based on minimization of the error between the observation and forward modeling only provides one of the best-fit models, which is usually band-limited. A complete solution should include both models and their uncertainties, which requires drawing samples from the posterior distribution. A global optimization method called very fast simulated annealing (VFSA) is commonly used to approximate posterior distribution with fast convergence. Here I address some of the limitations of VFSA by developing a new stochastic inference method, named Greedy Annealed Importance Sampling (GAIS). GAIS combines VFSA with greedy importance sampling (GIS), which uses a greedy search in the important regions located by VFSA to attain fast convergence and provide unbiased estimation. I demonstrate the performance of GAIS on post- and pre-stack data from real fields to estimate impedance models. The results indicate that GAIS can estimate both the expectation value and the uncertainties more accurately than using VFSA alone. Furthermore, principal component analysis (PCA) as an efficient parameterization method is employed together with GAIS to improve lateral continuity by simultaneous inversion of all traces.

The second part of my research involves estimation of reservoir permeability models and their uncertainties using quantitative joint inversion of dynamic measurements, including synthetic production data and time-lapse seismic related data. Impacts from different objective functions or different data sets on the model uncertainty and model predictability are investigated as well. The results demonstrate that joint inversion of production data and time-lapse seismic related data (water saturation maps here) reduces model uncertainty, improves model predictability and shows superior performance than inversion using one type of data alone.

Return to top | Return to Index


DYNAMICS OF DILATIVE SLOPE FAILURE

Yao You, Ph.D.

University of Texas at Austin, December 2013

Supervisors: Peter Flemings and David Mohrig

129 pages, 67 references, 3 tables

Submarine slope failure releases sediments; it is an important mechanism that changes the Earth surface morphology and builds sedimentary records. I study the mechanics of submarine slope failure in sediment that dilates under shear (dilative slope failure). Dilation drops pore pressure and increases the strength of the deposit during slope failure. Dilation should be common in the clean sand and silty sand deposits on the continental shelf, making it an important mechanism in transferring sand and silt into deep sea. Flume experiments show there are two types of dilative slope failure: pure breaching and dual-mode slope failure. Pure breaching is a style of retrogressive subaqueous slope failure characterized by a relatively slow (mm/s) and steady retreat of a near vertical failure front. The retreating rate, or the erosion rate, of breaching is proportional to the coefficient of consolidation of the deposit due to an equilibrium between pore pressure drop from erosion and pore pressure dissipation. The equilibrium creates a steady state pore pressure that is less than hydrostatic and is able to keep the deposit stable during pure breaching. Dual-mode slope failure is a combination of breaching and episodic sliding; during sliding a triangular wedge of sediment falls and causes the failure front to step back at a speed much faster than that from the breaching period. The pore pressure fluctuates periodically in dual-mode slope failure. Pore pressure rises during breaching period, weakens the deposit and leads to sliding when the deposit is unstable. Sliding drops the pore pressure, stabilizes the deposit and resumes breaching. The frequency of sliding is proportional to the coefficient of consolidation of the deposit because dissipation of pore pressure causes sliding. Numerical model results show that more dilation or higher friction angle in the deposit leads to pure breaching while less dilation or lower friction angle leads to dual-mode slope failure. As a consequence, pure breaching is limited to thinner deposits and deposits have higher relative density.

Return to top | Return to Index


IMAGING EVIDENCE FOR HUBBARD GLACIER ADVANCES AND RETREATS SINCE THE LAST GLACIAL MAXIMUM IN YAKUTAT AND DISENCHANTMENT BAYS, ALASKA

Julie Zurbuchen, Bachelor of Science

University of Texas at Austin, May 2014

Supervisor: Sean P. S. Gulick

38 pages, 29 references, 1 table

As glaciers advance and retreat, they leave erosional surfaces, retreat sequences, morainal banks, and terminal moraines. These features can be imaged and interpreted in seismic reflection data to gain insight into ice routing, ice-sediment processes, and preserved glacial history. High-resolution 2-D multi-channel seismic data gathered on the August 2012 UTIG-USGS National Earthquake Hazards Reduction Program survey of Disenchantment and Yakutat Bays have provided understanding of the advance pathways of Hubbard Glacier and the glacial history of the bays.

These data show evidence of two unconformities appearing in the form of channels and interpreted to be glacial advance and retreat paths. The youngest observable channel, thought to have culminated near the end of the main phase of the Little Ice Age (LIA), is only imaged in Disenchantment Bay and ends at a terminal moraine near Blizhni Point. An older channel, thought to be from an advance that culminated in the early phase of the LIA, extends from Disenchantment Bay into Yakutat Bay, staying to the northeast of Yakutat Bay, and then turning southward at Knight Island, and terminating on the southeastern edge of Yakutat Bay. Our interpretation suggests that the Hubbard Glacier has repeatedly advanced around the east side of Yakutat Bay in Knight Island Channel, possibly due to the presence of Malaspina Glacier cutting off access to the central Yakutat Bay during a time of mutual advance. Interpretation of seismic facies within these two unconformities suggests that Hubbard Glacier exhibits rapid retreats and Disenchantment Bay is subject to numerous episodes of outburst flooding and morainal bank collapse.

Return to top | Return to Index


UT Library Online | UT Austin Web Central | www@lib.utexas.edu
© the University of Texas Libraries . The University of Texas at Austin.