Dissertations / Theses on the topic 'Geology – Texas – Burnet County'

<p> The Spraberry Formation is a Leonardian age submarine fan deposit restricted to the Midland Basin. The formation consists of very fine-grained sandstone, medium to coarse grain size siltstones, organic shales and carbonate mudstones. These rocks show variability in sedimentary structures and bedding types varied from thinly laminated to convolute laminations. Bioturbations were present in some samples and soft sediment deformation, such as water escape features, sediment loading and flame structures. </p><p> The Spraberry Formation is a naturally fractured reservoir with low porosity and low matrix permeability. Porosity measured varied from 2% in rocks with poor reservoir quality such as the argillaceous siltstone and mudstone while good reservoir rocks had an average porosity of 9%. Seven lithofacies were identified based on sedimentary structures, grain size and rock fabrics. Petrographic analysis showed four porosity types: (1) intragraular porosity; (2) dissolution porosity; (3) fracture porosity and (4) intergranular porosity. Fractured porosity was only observed in the argillaceous siltstone lithofacies. </p><p> The prominent diagenetic influences on the Spraberry Formation are: quartz cementation, quartz overgrowth, illtization of smectite, feldspar dissolution, clay precipitation, carbonate cementation, formation of framboidal pyrite and fracture formation. These diagenetic features were observed using scanning electron microscope (SEM) and in thin sections. Generally, petrophysical properties, such as porosity and permeability, vary gradually from reservoir rocks to non-reservoir rock. Observed trends where: 1) increasing organic and argillaceous content with decreasing porosity and 2) increasing carbonate sediments and calcite cements with decreasing porosity. Mineralogical analysis from FTIR showed an abundance of quartz and calcite, while illite is the prominent clay mineral observed in all samples.</p>

<p> The recent and rapid growth of horizontal drilling in the Anadarko basin necessitates newer studies to characterize reservoir and source rock quality in the region. Most oil production in the basin comes from the Granite Wash reservoirs, which are composed of stacked tight sandstones and conglomerates that range from Virgillian (305&ndash;299 Ma) to Atokan (311&ndash;309.4 Ma) in age. By utilizing geophysical well logging data available in raster format, the Granite Wash reservoirs and their respective marine flooding surfaces were stratigraphically mapped across the regional fault systems. Additionally, well log trends were calibrated with coincident core data to minimize uncertainty regarding facies variability and lateral continuity of these intervals. In this thesis, inferred lithofacies were grouped into medium submarine fan lobe, distal fan lobe, and offshore facies (the interpreted depositional environments). By creating isopach and net sand maps in Petra, faulting in the Missourian was determined to have occurred syndepositionally at the fifth order scale of stratigraphic hierarchy.</p><p>

<p>The origin of the Mule Ear Spring Tuff (Tmet) member of the Chisos Formation of the Big Bend Group in Big Bend National Park (BBNP) (Maxwell et al., 1967) and its relationship to Sierra Quemada (SQ) is debated (a caldera versus a ring dike complex without associated collapse), as well as how the exact age of the Tmet relates to volcanic material present in and around the SQ structure. The main objectives were to identify main types of clasts present within the lithic-rich tuff and to determine the relative age of the lithic-rich tuff within SQ in order to help identify the type of structure and the type of activity&mdash;caldera with collapse or simply a ring dike. </p><p> Detailed lithologic and petrologic descriptions of hand samples and thin sections were performed to determine relationships of the clasts within the lithic-rich tuff to units outside of SQ. The identification and comparison of the samples produced a relative age of approximately 30.3 Ma to 33.7 Ma for the activity within SQ, which is comparable to published ages of Tmet. </p><p> Measurements of the clasts, along with the apparent thickness of the lithic-rich tuff, were compared with studies done on lithic-rich accumulations within modern and ancient calderas. The concentration and sizes of the clasts within the lithic-rich tuff from SQ are comparable to, or larger than, calderas with similar diameters to the SQ structure. The results are compatible with the formation of a typical resurgent caldera. The lack of lithic fragments younger than Tmet within the tuff is compatible with the age of Tmet. Therefore, the age of activity and formation of SQ occurred approximately 34 Ma. </p>

This study elucidates the underlying relationships for the distribution of oak landcover on bedrock and soil orders in two counties in Texas and one in Oklahoma. ESRI's ArcGis and ArcMap was used to create surface maps for Denton and Coke Counties, Texas and Choctaw County, Oklahoma. Attribute tables generated in GIS were exported into a spreadsheet software program and frequency tables were created for every formation and soil order in the tri-county research area. The results were both a visual and numeric distribution of oaks in the transition area between the eastern hardwood forests and the Great Plains. Oak distributions are changing on this transition area of the South Central Plains. The sandy Woodbine and Antlers formations traditionally associated with the largest oak distribution are carrying oak coverage of approximately 31-32% in Choctaw and Denton Counties. The calcareous Blackland and Grand Prairies are traditionally associated with treeless grasslands, but are now carrying oak and other tree landcover up to 18.9%. Human intervention, including the establishment of artificial, political and social boundaries, urbanization, farming and fire control have altered the natural distribution of oaks and other landcover of this unique georegion.

The Aubrey Clovis site is one of the oldest late-Pleistocene sites in North America, dated to ~11,550 B.P., and contains two camps with a range of lithic debitage, numerous hearths, and excellent faunal preservation. Couched in rules of classification, a series of artifact distributions are analyzed with qualitative and quantitative techniques, including maps produced in a geographic information system (GIS) and tests of artifact associations using correlation statistics. Theoretical and methodological protocols are promoted to improve spatial analysis in archaeology. The results support the short-term occupation interpretation and expose the differential patterning among bone, stone, and raw materials distributions. The spatial structure and diverse content of the site challenge models of Clovis-age people as strictly big game hunters.

Eighty-nine caves and sinkholes were investigated in the Edwards Aquifer recharge zone in Bexar County, Texas. The study examined their hydrogeologic and topographic origins and distribution, relationships to major fracture traces, quantity of recharge into the aquifer and degree of sensitivity towards degradation of the aquifer’s water quality. Groundwater traces were attempted to determine aquifer flow routes, time of groundwater travel, groundwater volume within conduits, and the aquifer’s capacity for dilution and dispersion of recharged contaminants. Trends in water quality were examined to quantify the volume and variety of contaminants recharged into the aquifer and to determine the effects of urbanization upon the Edwards Aquifer. The Edwards recharge zone was hydrogeologically assessed to rate the sensitivity of its areas. Socio-political impacts on recharge zone development were also examined. Based on the results of the above outlined research method, the conclusions of this investigation are that caves and sinkholes contribute substantial recharge into the Edwards Aquifer, rapidly transmit that recharge to the aquifer and are sensitive sites for potential contamination. The entire recharge zone was determined to be very sensitive to contamination. No significant differences were found between areas within the recharge zone to scale their degree of sensitivity. Major conduit flow networks were found to exist within the aquifer and their groundwater flow paths could be traced. Urban development of the Edwards recharge zone was shown to decrease the volume of recharge and degrade the aquifer’s water quality. No significant detrimental effects on the aquifer were observed. The volume of diminished recharge and the concentration of recharged contaminants that were necessary to produce significant adverse effects on the aquifer were not determined due to lack of precipitation during the study period and inconclusive groundwater tracings. It was recommended that further development of the recharge zone be suspended until the effects of urbanization are quantified.

The Llano Uplift of central Texas contains the largest exposure of Mesoproterozoic rocks along southern Laurentia and is thus crucial to the understanding of orogenesis and plate reconstructions along a portion of one of the largest orogens in the world. Most of the current understanding of the Mesoproterozoic tectonic evolution of southern Laurentia comes from the southeastern portion of the Llano Uplift. To fully characterize the tectonic evolution Llano Uplift, detailed mapping is necessary in the less-studied western Llano Uplift. The Mesoproterozoic Llano Uplift exposes mid-crustal, poly-deformed and metamorphosed schists and gneisses and abundant pre- to post-tectonic granites through an erosional window of Phanerozoic sedimentary rocks. Three lithologic groups were mapped in the western Llano Uplift, from structural highest to lowest these are the Valley Spring Gneiss (VSG), Lost Creek Gneiss (LCG) and Packsaddle Schist (PS). The VSG consists of pelitic schists and pink quartzofeldspathic schists and gneisses. The LCG is a thick, homogeneous package of medium- to coarse-grained augen granite gneiss, interpreted to be a deformed, coarse-grained, porphyritic pluton. The PS consists of a heterogeneous package of interlayered quartzofeldspathic gneisses, amphibolites and minor marbles. These lithologies are consistent with the PS and VSG domains described in the southeastern Llano Uplift (Mosher, 1998; Reese et al., 2000). The exotic Coal Creek Domain (CCD) of the southeastern Llano Uplift is not observed in the western Llano Uplift. The western Llano Uplift, including the VSG, LCG and PS, records a deformational history that resulted in multiple fold generations (F1-F5) and is characterized by a penetrative axial planar foliation (S1-S5). F2s are isoclinal folds of S0 (primary layering) and S1 that locally fold F1 axial planes and have steeply plunging and generally easterly trending hinge lines. F3 folds are locally developed, nearly colinear and coplanar with F2s, tight to open, and fold all previous structures (F1/F2) and fabrics (S1/S2). F4s are open folds with northeast-trending axial traces that occur on a regional-scale. F5s are open to tight folds of all previous structures, with hinge lines that are primarily southeast trending and steeply plunging. S0 to S3 orientations vary from north to east dipping because of reorientation by younger folds. S4 foliations strike to the northeast and S5 foliations are northwest striking and nearly vertically dipping. Late left-lateral shear zones (D6) with generally an easterly trend and boudinage affects the VSG, LCG and VSG in this study area and is commonly associated with unfoliated granite material. Four generations of intrusive granitic sills and dikes are documented and provide relative and absolute age constraints on deformation. The oldest recognized deformation (D1-D3) is constrained between 1253 +5/-3 Ma and 1126 +5/-4 Ma (Roback, et al., 1999). D4 and D5 deformation are constrained between 1126 +5/-4 Ma and 1076 ± 5 Ma (Roback, et al., 1999). Although a change in metamorphic conditions is documented to have occurred between D2 and D3, metamorphic fabrics and assemblages indicate granulite facies conditions during D1, D2 and D3. Amphibolite facies metamorphism occurred during D4 and presumably D5. Deformation in the eastern Llano Uplift has a similar polyphase deformational history to that recorded here for the western Llano Uplift. Deformation in the eastern Llano Uplift is similarly constrained between ca. 1238 to 1091 Ma. In addition, the youngest fold generation (F5) can be directly correlated in orientation and timing from the western to the eastern Llano Uplift, and is constrained between ca. 1119 and 1091 Ma in the eastern uplift. Both the western and eastern Llano Uplift contain late shear zones and extensional structures. Structural differences between the western and eastern Llano Uplift include differences in style and orientation of all but the latest (D5 and D6) structures. In addition, dip of fabrics and, therefore, structural stacking of lithologic domains is opposite, and no mylonite zones were identified in the west. In conclusion, the lithologic domains appear to correlated across the Llano Uplift based upon gross lithologic similarities and the tectonic evolution is similar to the well-studied eastern Llano Uplift, though the kinematics and orientations differ. These conclusions may require that the kinematics of deformation in the southeastern uplift were controlled by the presence of the exotic island arc terrane (CCD) whereas the kinematics of deformation in the western uplift were controlled by continent-continent collision.<br>text

Hydrocarbon producing, deep-water Cisco sands along the Eastern Shelf were studied in the vicinity of Flowers "Canyon Sand" Field to develop a depositonal model explaining their origin, geometry, and style of deposition. Regional correlations and subsurface mapping indicate that producing sands were deposited within the Swastika lithogenetic unit, which contains a network of shelf-margin fluvial/deltaic, slope, and basin depositional systems deposited between transgressive Gunsight and Ivan Limestones. The sands are not "Canyon", but Virgilian in age. During Swastika time a wedge of sediments up to 1100 feet thick was deposited in the study area in response to westward progradation of shelf-margin deltas. Standard mapping techniques and detailed correlations using nearly 700 well logs and the examination of 3 cores indicate that this wedge can be divided into three principal systems: (1) a sand-dominated turbidite, basin and lower slope system, which constitutes the reservoir facies, (2) a shale-rich prodelta/slope system punctuated by slope channel filled gullies, and (3) a sand-dominated shelf-margin fluvial/deltaic system. Ten deltaic lobes, averaging 2 miles in diameter, were recognized. These lobes may have been deposited during a lowstand of sea level. Elongate/lobate geometry and rapid shifting of lobes indicate high depositional rates. Shelf-margin instabilities associated with deltas led to prodelta/slope slumping, gully formation, and generation of turbidity currents. Turbidity currents generated by the earliest deltas to breach the shelf break were of sufficient magnitude to erode a broad, shallow inner-fan valley at the base of the slope. This valley initially focused turbidity currrents onto a base-of-slope terrace, which was mapped on top of the Gunsight Limestone, and formed by differential compaction over a subjacent Canyon delta or carbonate buildup. Low gradients associated with this terrace gave rise to a sediment trap. Nearly all existing production in Flowers Field is established above this terrace. Turbidites deposited within this phase of Swastika evolution display characteristics of an elongate/radial type fan deposit. Continued deltaic progradation filled the inner-fan valley. Once this valley was breached, a network of small channels originating as gullies along slopes in front of the advancing Swastika delta system transported sediment down the slope to form an aggrading/prograding wedge of turbidite and volumetrically less significant grain flow deposits. This change in depositional style led to superposition of what is best classified as an elongate/debris apron type system over the earlier elongate/radial deposits. A critical conclusion is that no single channel developed into a large canyon feeder system, which resulted in facies relationships that differ from commonly accepted models calling on a prolonged point source. Given the importance of turbidite sands in many petroliferous basins, application of the delta-fed model to appropriate turbidite systems can improve exploration strategies.<br>text

A boulder bed unit in the upper Haymond Formation (Pennsylvanian), generally believed to be olistostromes, is exposed in the eastern Marathon Basin, west Texas. Two localities of this unit (Housetop Mountain and Clark Butte) contain clasts derived from several formations found within the basin, as well as exotic Devonian metamorphic and volcanic rocks. This report describes a third previously unstudied site (Martin Ranch locality) that contains clasts of exotic Middle Cambrian shelf limestones. These limestones provide a key to the Early Paleozoic history of the Marathon region. The boulder beds lie in the upper part of the Haymond Formation. At the Martin Ranch locality they form a zone that is traceable for 6.6 km along strike and is up to 230 m thick. These boulder beds contain interbedded units of massive, unstratified, pebble- to boulder-bearing mudstone, thickly bedded, massive sandstone, lenses of pebbly sandstone, and deformed flysch beds. About 80 percent of the clasts found in the boulder beds at Martin Ranch are chert derived from several basin formations. Unique displaced slabs of bedded chert pebble conglomerate comprise about 10 percent of the clasts. Theses conglomerates were probably derived from upper fan-channel deposits within the lower Haymond Formation. Pennsylvanian limestone clasts redeposited from the basin facies of the Dimple Formation and clasts of exotic, late Middle Cambrian limestones each comprise about 5 percent of the clasts. These Cambrian limestones, older than any formation in the Marathon Basin, contain a fauna characteristic of the seaward edge of the cratonic carbonate shelf. The presence of the Cambrian clasts constrains the location of the North American shelf edge during the Cambrian, placing it at least 120 km southeast of the present day Marathon Basin. Both the Martin Ranch and Housetop Mountain boulder beds are composed mainly of clast-bearing, matrix-supported mudstone which have pebbly sandstone, massive sandstone, and flysch beds interstratified with the mudstone and represent periodic deposition of debris flows, slumps, slides, and turbidites interspersed with normal basin deposition of flysch facies rocks. However, different clast types are found at the two localities. The Martin Ranch locality has clasts of Cambrian limestone and chert pebble conglomerate, the latter up to 90 m in length, that are absent at the other localities. Exotic Pennsylvanian limestone clasts and exotic Devonian metamorphic and volcanic rocks, common at Housetop Mountain, are rare or missing at Martin Ranch. The Clark Butte locality is unique because it lacks the mudstone which dominates the other two localities. Instead, the matrix is composed of a pebbly sandstone and conglomerate associated with thick sandstone beds. The boulder beds at this locality may represent upper fan channels and channel-lag deposits. The turbidites and olistostromes resulted from recycling of the southern edge of the tectonic basin as the advancing Ouachita thrusts uplifted the pre Haymond strata. Most of the clasts were from older basin formations exposed by these faults; however one of these thrusts also uplifted slivers of exotic Middle Cambrian limestone. Earthquakes probably triggered slumps and rock falls off the fault scarps. As the boulders travelled downslope plowing through the slope sediments, they accumulated more material. This combination of slide debris and slope mud turned the slumps and slides into debris flows. Between episodes of debris flows and turbidity currents, normal basin deposition of thinly bedded turbiditic sandstone and pelagic shale occurred.<br>text