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    Catahoula formation of the Texas Coastal Plain : origin, geochemical evolution, and characteristics of uranium deposits
    (University of Texas at Austin. Bureau of Economic Geology, 1980) Galloway, William E.; Kaiser, W. R.
    The Catahoula Formation is composed of ancient fluvial sediments that controlled a wide range of water/sediment interactions responsible for uranium mobilization, transportation, and concentration. Uranium was released from volcanic glass deposited within the Catahoula through early pedogenic and diagenetic processes. Soil development produced plasmic clay cutans, oxide nodules, and vacuoles; open hydrologic system diagenesis produced shard-moldic porosity and clinoptilolite pore-filling cement. Pedogenesis was the most efficient process for mobilizing uranium. Original uranium content in fresh Catahoula glass is estimated to have averaged at least 10 ppm; about 5 ppm was mobilized after deposition and made available for migration. Uranium was transported predominantly as uranyl bicarbonate ion by oxidizing neutral to mildly basic, bicarbonate- and silica-rich ground waters. Uranium transport is continuing today in parts of the Catahoula aquifer in oxidizing (+240to +300 mV) and neutral to highly basic (pH 7 to 11) ground waters. The chemistry of modern Catahoula ground waters reflects down flow ionic evolution and localized mixing with compositionally diverse waters discharged vertically from underlying aquifers. Chlorinity mapping reveals modern ground-water flow patterns, suggests hydrodynamic interpretation of alteration-front geometry, and provides clues to flow dynamics extant during earlier aquifer evolution. Isochemical contours reproduce geometries reminiscent of alteration fronts, reveal vertical discharge of saline waters across aquitards and up fault zones, and demonstrate updip movement of sulfide-rich waters apparently intruded into shallow aquifers along faults. Six uranium deposits representative of the spectrum of Catahoula ores were studied. Uranium-bearing meteoric waters were reduced by reaction with pre-ore stage pyrite formed by extrinsically introduced fault-leaked sulfide (for example, Bruni deposit) or intrinsically by organic matter (for example, Washington-Fayette deposit). Uranium was concentrated in part by adsorption on Ca-montmorillonite cutans, amorphous TiO2, and/ or organic matter followed by uranyl reduction to U4+ in amorphous uranous silicates. Field and geochemical evidence shows that clinoptilolite, a potential adsorber of uranium, is not correlative with mineralization. Calcite is pervasive throughout host sands but shows no spatial or temporal relationship to uranium mineralization. Waters presently associated with Catahoula uranium deposits are oxidizing, alkaline waters of high ionic strength and are not appropriate models for the primary mineralizing waters, which are postulated to have been reducing, acid waters of low to moderate ionic strength. The presence of marcasite and uranium together at the alteration front strongly supports an acid pH during Catahoula mineralization. Maximum adsorption and minimum solubility of uranium occur at approximately pH 6 in carbonate-rich waters. Solution and mineral equilibria were used to test activities and mineral saturation against the occurrence of uranium in four deposits. Log activity ratios of individual waters more highly supersaturated with respect to montmorillonite, taken from montmorillonite-clinoptilolite activity diagrams, show a positive correlation with uranium mineralization. High Ca2+, Mg2+, Al(OH)-4, and H+ activities promote the formation of montmorillonite relative to clinoptilolite. High saturation ratios for montmorillonite show fair correlation with mineralization. The mineral-solution equilibria approach is a potential method of geochemical exploration.
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    Molluscan distribution in Copano Bay, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1980) Calnan, Thomas R.
    Benthic samples were collected on a 1-mi grid from Copano Bay, Texas, in March and April, 1976. Seventy-four molluscan species, including 33 pelecypods, 40 gastropods, and 1 scaphopod were taken from 93 stations in Copano Bay. Molluscan distribution was correlated with gross sediment, salinity, feeding type, and total organic carbon content. Seven sediment types were mapped in Copano Bay. The mud and sand end-members had fewer molluscan species and live individuals, whereas the muddy sands had the highest number of live individuals. Salinity averages from 1926 to 1976 have varied from less than 10 parts per thousand to 36 parts per thousand yearly. Salinities from 1971 to 1976 averaged less than 15 yearly. Fourteen of the 25 living molluscan species were euryhaline marine and could tolerate the highly variable salinities. Dead stenohaline marine species were common, but only one living stenohaline species was found. The two most abundant feeding types, the deposit and suspension feeders, numerically dominated in the muddy sands and muddy shells, respectively. Generally, stations with a high total organic carbon content also had a large population of deposit feeders, although there were some exceptions. Extensive Crassostrea virginica reefs are present in Copano Bay. Whole shells or fragments of oyster shell were found in 75 percent of the samples, and six stations had live Crassostrea. Odostomia impressa and Ischadium recurvum were the predominant mollusks at the reef stations.
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    Report of Investigations No. 131 Origin and Diagenesis of Cap Rock, Gyp Hill and Oakwood Salt Domes, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1983) Kreitler, Charles W.; Dutton, Shirley P.
    Petrographic and geochemical studies of caprock core from two salt domes, Gyp Hill in South Texas and Oakwood in East Texas, reveal the significantly different diagenetic histories of each dome. Cap rock on Gyp Hill is now forming within a shallow meteoric aquifer. In contrast, cap rock on Oakwood Dome formed principally during the geologic past within deep, saline aquifers in the East Texas Basin. Gyp Hill cap rock, which is 890 ft (271 m) thick, is composed of 490 ft (149 m) of anhydrite overlain by 400 ft (122 m) of gypsum. Uncemented anhydrite sandstone marks the salt/cap-rock interface. From 13 ft (4 m) above the interface to the top of the anhydrite, porosity is occluded by poikilotopic gypsum cement. Occurrence of gypsum cement indicates low-temperature, low-salinity conditions during caprock formation; that is, dome dissolution is occurring in a shallow meteoric aquifer. The overlying gypsum results from hydration of anhydrite by meteoric ground water. Oakwood cap rock, which is 450 ft (137 m) thick, is composed of 256 ft (78 m) of anhydrite overlain by 194 ft (59 m) of calcite. In contrast to Gyp Hill anhydrite, Oakwood anhydrite is entirely devoid of gypsum cement except at the interface between anhydrite and calcite. The anhydrite has been recrystallized into a moderately well developed granoblastic texture that is indicative of high-temperature and high-pressure conditions. Fluid inclusions in the salt at the salt/cap-rock interface represent waters from the last dissolution event. The delta 18O of water from a fluid inclusion is +/-5.4 ppm, indicating a deep-basin origin of the water. The anhydrite section is considered to have accumulated during salt dissolution under deep, high-temperature, saline conditions. Timing of the development of major rim synclines surrounding Oakwood Dome indicates that the anhydrite cap rock formed in Early Cretaceous time. The calcite section of the cap rock is composed of alternating layers of dark and light calcite. Petrographic, geochemical, and isotopic data on dark calcite indicate that the dark calcite is the product of calcium sulfate reduction by hydrocarbons in a saline, deep-basin fluid. Another deep-basin fluid, more enriched in Sr, Ba, Mg, and Mn, dissolved some of the dark calcite, which then reprecipitated as coarsely crystalline light calcite. The only effect of meteoric water on either the anhydrite or the calcite section of the Oakwood cap rock is the presence of gypsum in the calcite/anhydrite transition zone. Anhydrite cap rock beneath the salt overhang of Oakwood Dome (~6,000 ft deep) had an origin similar to that of the cap rock on top of the dome. Petrographic analyses of cap rock from Rayburn's and Vacherie Domes (Louisiana) and Cypress Creek and Richton Domes (Mississippi) further substantiate the two different types of cap rock. The cap rock from Rayburn's Dome is similar to that at Gyp Hill Dome, whereas the cap rock from Vacherie is similar to Oakwood Dome cap rock. The mineralogy and textures observed in cap rocks from Richton and CypressCreek Domes indicate that they are intermediate between Gyp Hill and Oakwood cap rocks. Petrographic and geochemical studies of cap rock are important in evaluating the hydrologic stabilities of salt domes being considered as repositories for high-level nuclear wastes. Anhydrite cap rocks such as those at Oakwood Dome contain recrystallized anhydrite, are devoid of gypsum, have a tight cap-rock/salt contact, and formed early in the geologic history of the basin. There is no evidence within the cap rock of recent salt dissolution by meteoric ground water. In contrast, cap rocks such as those at Gyp Hill contain unrecrystallized anhydrite, are cemented with gypsum, and have both uncemented anhydrite sands and a cavity at the salt/cap-rock contact. They also exhibit ample evidence of recent salt dissolution by meteoric water, a condition unacceptable in a salt dome being considered as a high-level nuclear waste repository.
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    Relation of Ogallala formation to the southern High Plains in Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1964) Frye, John Chapman, 1912-
    Studies along the southern and southeastern borders of the High Plains have demonstrated the presence of outliers of fossiliferous Ogallala Formation in Borden and Scurry counties and have documented the occurrence of Pliocene deposition as far southeast as Sterling County. The limit of characteristic Ash Hollow seed floras is extended to the southeast. An abandoned Pliocene and Pleistocene valley is described across a prong of Edwards Plateau south of Big Spring, and the drainage of the late Pleistocene Lake Lomax is determined to have occurred in pre-Bradyian Wisconsinan time. A meaningful physiographic boundary cannot be drawn between the southern limits of the High Plains and the Edwards Plateau.
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    Statistical Analysis of Lineaments and their Relation to Fracturing, Faulting, and Halokinesis in the East Texas Basin
    (University of Texas at Austin. Bureau of Economic Geology, 1981) Dix, Owen R.; Jackson, M.P.A.
    Lineament analysis is part of a broad spectrum of structural studies employed to determine the tectonic stability of the East Texas Basin. Such information is necessary to assess the suitability of East Texas salt domes as possible repository sites for the storage of high-level nuclear wastes. A sequence of statistical operations was designed to identify and assess the significance of lineament preferred orientation by means of a variety of statistical tests or parameters, including vector summation, length weighting, X2, F, and t testing, the Bernshtein accuracy criterion, and an index of preferred orientation. Black-and-white aerial photographs, at scales between 1:17,400 and 1:25,500, and band-5 Landsat imagery were analyzed. Well-defined, northeast-trending and northwest-trending lineament populations are present throughout the East Texas Basin. The northeast trend, comprising two peaks oriented at 045 and 055, corresponds to the orientation of the Mexia-Talco peripheral fault zone, to subsurface faults in the center of the basin, and to some lithologic contacts. The northwest trend comprises two peaks oriented at 310 and 325. Both the northeast and northwest trends are thought to result from preferential directions of fracture induced by interference folding at depth. This folding is caused by halokinesis and is reflected in the regional gravity field. The Elkhart - Mount Enterprise fault zone has exerted little noticeable effect on the regional lineament pattern, mainly because of its subparallel orientation. Areas above shallow salt domes, particularly those in the southern part of the basin, are associated with higher lineament densities and lower preferred orientation of lineaments than are non-dome areas or areas above deep salt diapirs; this probably reflects radial and concentric fault and fracture patterns above the shallow domes. Analysis of computer-generated, geologically meaningless sets of lineaments strongly suggests that confidence levels of 99 percent are necessary to exclude randomly generated peaks, and that the significance of orthogonal pairsets has been exaggerated in the literature.
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    Report of Investigations No. 123 Petroleum Potential of the Palo Duro Basin, Texas Panhandle
    (University of Texas at Austin. Bureau of Economic Geology, 1982) Dutton, Shirley P.; Goldstein, Arthur G.; Ruppel, Stephen C.
    The Palo Duro Basin seemingly has all the elements necessary for hydrocarbon generation and accumulation: reservoirs, traps, source rocks, and sufficient thermal maturity. Porous facies in pre-Pennsylvanian, Pennsylvanian, and Permian strata are potential hydrocarbon reservoirs. Within the pre-Pennsylvanian section, shallow-marine carbonates of both Ordovician (Ellenburger Group) and Mississippian age have sufficient porosity and permeability for hydrocarbon accumulation. Three main exploration targets of Pennsylvanian and Wolfcampian age are (1) granite-wash sandstones, (2) shelf-margin carbonates, and (3) elongate-delta sandstones. Granite wash was deposited in fan deltas adjacent to fault-bounded, basement uplifts around the basin margins. Porous facies are braided-channel, fan-plain, and distal-fan deposits. Porous carbonates developed through time along the different positions of the shelf margins. Organic-rich basinal shales are juxtaposed against the porous shelf-margin facies. High-constructive, elongate-delta deposits in the southeastern part of the basin retain high porosity in bar-finger (channel-mouth bar) sandstones. In younger strata, dolomites in the Clear Fork (Leonardian) and the San Andres (Guadalupian) Formations are reservoirs along the Matador Arch. However, porosity in these units apparently pinches out to the north. Both stratigraphic and structural traps occur in the basin. Porosity pinch-outs form the primary stratigraphic traps. Major faults are associated with the Amarillo Uplift; smaller faults have been identified in the deeper parts of the basin. Most faults are thought to have existed before the Pennsylvanian and to have been reactivated by a northwest maximum principal compression. Fracturing adjacent to some faults may have created fractured reservoirs. The Palo Duro Basin contains source rocks of sufficient quality to generate hydrocarbons. Pennsylvanian and Wolfcampian shales contain up to 2.4 percent total organic carbon (TOC) and are fair to very good source rocks. Lipid-rich organic matter occurs primarily in basinal shales. Kerogen color and vitrinite reflectance, which measure thermal maturity, indicate that temperatures were sufficiently high to begin to generate hydrocarbons from lipid-rich organic matter. Pennsylvanian and Wolfcampian kerogen is yellow orange to orange. Average reflectance in Pennsylvanian vitrinite is 0.52 percent; in Wolfcampian samples the average reflectance is 0.48 percent. Recent oil discoveries in the Palo Duro Basin confirm that oil was generated.
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    Report of Investigations No. 125 Atoka Group (Lower to Middle Pennsylvanian), Northern Fort Worth Basin, Texas: Terrigenous Depositional Systems, Diagenesis, and Reservoir Distribution and Quality
    (University of Texas at Austin. Bureau of Economic Geology, 1982) Thompson, Diana Morton
    The Fort Worth Basin, in North-Central Texas, is a late Paleozoic foreland basin that was downwarped during the Early to Middle Pennsylvanian Period in response to tectonic stresses that also produced the Ouachita Thrust Belt. The Atoka Group was deposited during the initial westward progradation of chert-rich terrigenous clastics derived both from the Ouachita Thrust Belt and locally from the Muenster Arch across the northern part of the basin. At the northern end of the basin, the Atoka Group interfingers with arkosic conglomerates (granite wash) derived from the Red River-Electra Arch. The granite wash is time equivalent but constitutes a separate stratigraphic sequence. The Atoka Group contains three distinct packages of terrigenous deposits: (1) the lower Atoka lithogenetic unit, interpreted to be a fluvially dominated fan-delta system, (2) the upper Atoka "Davis" lithogenetic subunit, interpreted to be a system of coalesced wave-dominated deltas, and (3) the upper Atoka "post-Davis" lithogenetic subunit, interpreted to be a thin, poorly integrated, fluvially dominated fan-delta system. Atoka Group sandstones are quartz-rich feldspathic (chert) litharenites. The most significant diagenetic events were silica dissolution and cementation. Net porosities of 10 to 15 percent are the result of the preservation of original porosity in between quartz overgrowths and the creation of secondary porosity by chert grain dissolution. Highest porosities occur in channel-fill and coarse-grained fan-delta plain facies. The Atoka Group has a cumulative production history of more than 160 million barrels (oil plus gas equivalent). Production and reservoir distribution and quality are facies controlled. Most oil and gas fields coincide with the distribution of lower Atoka fan-delta lobe complexes. Minor production is located along the axes of upper Atoka "post-Davis" fan-delta complexes.
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    Formation of the Wink Sink, A Salt Dissolution and Collapse Feature, Winkler County, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1982) Baumgardner, Jr., Robert W.; Hoadley, Ann D.; Goldstein, Arthur G.
    The Wink Sink in Winkler County, Texas, formed on June 3, 1980. Within 24 hours it had expanded to a maximum width of 360 ft (110 m). On June 5, 1980, maximum depth of the sinkhole was 110 ft (34 m), and volume about 5.6 million ft3 (158,600 m3). Between June 3 and June 6, 1980, a large area bordering the south rim of the sink subsided about 10 ft (3 m) relative to the north side. Further subsidence of 1,456 ft (44.4 cm) occurred along the southern rim between July 19 and December 12, 1980. A probable precursor of the sinkhole was a solution cavity that migrated upward by successive roof failures, thereby producing a collapse chimney filled with brecciated rock. Dissolution of salt in the Permian Salado Formation is inferred to have produced the solution cavity. Depth of the Salado ranges from 1,300 to 2,200 ft (396 to 670 m). Data on the size and initial depth of the solution cavity are unavailable. The Salado Formation in the region contains several dissolution zones. Occurrence of dissolution in the middle of the Salado evaporite sequence may have resulted from groundwater flow along fractured anhydrite interbeds. Water may have come in contact with salt by downward movement from overlying aquifers or by upward movement from underlying aquifers under artesian pressure. The Wink Sink lies directly above the Permian Capitan Reef, which contains water that is unsaturated with respect to sodium chloride. Hydraulic head of water from the reef is higher than the elevation of the Salado Formation but lower than the head in the Triassic Santa Rosa Formation, a near-surface fresh-water aquifer. Fracture or cavernous permeability occurs above, within, and below the Salado Formation, as indicated by the loss of circulation of drilling fluid in wells drilled near the sinkhole. Consequently, a brine density-flow cycle may be operating: relatively fresh water moves upward under artesian pressure and dissolves salt; the denser brine moves downward under gravity flow in the same fracture system. Alternatively, downward flow of water from aquifers such as the Santa Rosa Formation or Quaternary sediments above the salt is also a possible explanation for dissolution. A plugged and abandoned well that was located within the circumference of the sinkhole may have provided a conduit for water movement. Composition of water in the Wink Sink resembles that of water in nearby wells producing from the Quaternary alluvium and from the Triassic Santa Rosa Formation. Hendrick well number 10-A was drilled in 1928 at a site now within the circumference of the sinkhole. The well, which initially produced about 80 percent water from the Permian Tansill Formation, was plugged with cement and abandoned in 1964. The well was not used for brine disposal. Over 12 million barrels of salt water produced from the Hendrick Field were disposed of by injection into the Permian Rustler Formation during 1961. Waterflood projects in the Hendrick Field began in 1963 and are still in progress. Sinkholes similar to the Wink Sink occur in other areas of North America. Their morphology, associated strata, and mode of formation suggest that dissolution, brecciation, and surface subsidence commonly occur during their formation.
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    Report of Investigations No. 129 Environmental Geology of the Yegua-Jackson Lignite Belt, Southeast Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1982) Jackson, Mary L.W.; Garner, L.E.
    Environmental geologic maps of the Texas lignite belt were prepared in response to renewed production of lignite in Texas and enactment of Federal and State laws governing coal and lignite surface mining. The map area of this report encompasses the outcrop of the Yegua Formation and Jackson Group from south-central Texas to the Texas-Louisiana border. Yegua sediments are fluvial in outcrop, and deltaic in the deeper subsurface. Jackson deposits are predominantly of deltaic origin. Mapping involved interpretation of black-and-white, large-scale aerial photographs and extensive field work. Each of the 32 map units is defined in terms of substrate, soil, geomorphology, geologic process, vegetation, and land use. Additional information presented on the maps includes active and abandoned lignite mines and lignite resource blocks mapped by Kaiser and others (1980). Floodprone areas vegetation assemblages, and soil types presented on the maps provide basic data useful in mine planning. Correlation of sand outcrops with subsurface sand maps helps locate hydrologically sensitive areas that need careful consideration during lignite development. Environmental geologic maps can also aid public and private agencies in land use planning and land resource management.
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    Epeiric Depositional Models for the Lower Cretaceous Washita Group North-Central Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1978) Scott, R.W.; Fee, D.; Magee, R.; Laali, Hooman
    The Washita Group in North-Central Texas and southeastern Oklahoma consists of up to 114 m of intercalated shale, limestone, and sandstone that accumulated in the shallow, epicontinental sea of the East Texas Basin. The Ouachita-Arbuckle Mountains to the north supplied terrigenous sediments, and the Central Texas platform to the south was a site of carbonate deposition leeward of the shelf margin of the Stuart City trend. Eleven lithofacies of the Washita were deposited within a repeatedly subsiding shelf basin that received an intermittent supply of terrigenous sediment. The deepest seaway formed after subsidence and was filled by a south-to-north progression of facies consisting of mollusk-echinoid wackestone on a shallow shelf, transitional packstone shale of deeper water, calcareous and sandy shales of the deepest water, thin-bedded sandstone of the shallower water shoreface, wavy lenticular sandstone and shale of the distal delta front, and deltaic estuarine trough-crossbedded sandstone. Following basin filling, the carbonate shelf prograded northward, grading into nearshore sediments. This produced the south-to-north succession of mollusk-echinoid wackestone to either oyster packstone shale, oyster packstone and quartzitic-oyster packstone or quartzitic mollusk-echinoid packstone of the shoreface.
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    Depositional Patterns of Miocene Facies, Middle Texas Coastal Plain
    (University of Texas at Austin. Bureau of Economic Geology, 1979) Doyle, James David
    This report provides a data base for decisions about lignite mining and reclamation in the Wilcox Group of East Texas. Kaiser (1974, 1978) estimates that about 12.2 billion short tons of potentially strip-minable lignite resources occur in East and South Texas. About 8 billion tons of the lignite are within the Wilcox Group in the area of this study (Kaiser, 1978). Lignite production has grown from an estimated 2 million short tons in 1970 to 17 million tons in 1977 (Hawkins and Garner, 1978). Estimates of lignite demand indicate that all strippable reserves that can be economically recovered will be committed to use by 2000 (White, 1979). A set of environmental geologic maps, which accompanies this report, depicts the character of the land that will be affected by mining. The environmental geologic maps of the East Texas lignite belt provide an accurate inventory of land resources. The maps identify areas where mining is most likely to occur, areas of critical natural resources that could be affected by mining, such as aquifer recharge areas, and areas of natural hazards, such as floodplains. Principal areas of both active and planned surface mining are also located. Although interest in lignite mining prompted the preparation of these maps, their use is not limited to planning mining or to evaluating the effects of mining.
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    Wave-Dominated Delta Systems of the Upper Cretaceous San Miguel Formation, Maverick Basin, South Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1980) Weise, Bonnie R.
    Upward-coarsening sandstone units of the Upper Cretaceous San Miguel Formation in South Texas were deposited in wave-dominated deltas during minor regressive phases, periodically interrupting a major marine transgression. Sediments accumulated in the Maverick Basin within the Rio Grande Embayment. Cross sections and sandstone maps reveal that during deposition of the San Miguel, the Maverick Basin consisted of two subbasins that received sediments from the northwest and the north. Net-sandstone patterns show that the thickest parts of San Miguel sandstone bodies are generally strike oriented. Where preserved, updip fluvial systems are indicated by dip-aligned sandstone trends. San Miguel deltas vary considerably in morphology and compose a spectrum of wave-dominated delta types. Modern analogs of San Miguel deltas include the Rhone, Nile, Sao Francisco, Brazos, Danube, Kelantan, Grijalva, and Senegal deltas. Sandstone geometry ultimately depended on three primary factors: (1) rate of sediment input, (2) wave energy, and (3) rate of relative sea-level change. Original delta morphology was determined by all three factors, but the degree of reworking of deltaic sediments after delta abandonment was determined by wave energy and rate of transgression. The most common vertical sequences exhibited by the subsurface San Miguel coarsen upward from mudstone and siltstone to fine sandstone. Burrows are the dominant structures. Rare primary structures are small scale; large-scale crossbeds are observed only in outcrop. Strandplain or barrier-island facies sequences, which prevail in most wave-dominated delta deposits, are incomplete in the San Miguel. Typically, only the lower shoreface is preserved. Upper parts of the sequences, which normally containlarge-scale primary structures, were destroyed by marine reworking during subsequent transgression. Intense burrowing obliterated primary structures in the upper parts of the truncated shoreface sequences. Most of the San Miguel sandstones are arkoses, but the mineralogical composition of the sandstones changes vertically. Generally within each sandstone, quartz content increases upward with increasing mean grain size. Cements include sparry and poikilotopic calcite, quartz overgrowths, feldspar overgrowths, illite rims, and kaolinite. Porosity was eliminated principally by two types of calcite cement, which tend to cement completely the coarsest, best sorted, and originally most porous zones of the San Miguel sandstones. Zones of secondary porosity resulted from leaching of shell material, calcite cement, and feldspars. Laterally, the distribution of high secondary porosity and calcite-cemented zones is unpredictable.
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    Trace Elements in Soils of the South Texas Uranium District: Concentrations, Origin, and Environmental Significance
    (University of Texas at Austin. Bureau of Economic Geology, 1980) Henry, Christopher D.; Kapadia, Rajesh R.
    The environmentally sensitive trace elements molybdenum, arsenic, and selenium are concentrated with uranium in ore deposits in South Texas. Cattle grazing in some pastures in mining areas have contracted molybdenosis, a cattle disease resulting from an imbalance of molybdenum and copper. To determine natural concentrations of the elements in soils in the South Texas area and to evaluate possible effects of mining on adjacent agricultural land, two sets of soil samples were collected and analyzed for molybdenum, arsenic, selenium, and copper. Two hundred and fifty-six samples were collected in a statistically random design from soils developed on the Whitsett Formation, Catahoula Formation, or Oakville Sandstone, the major uranium hosts of the area, and 182 samples were collected nonrandomly from areas of mining or mineralization to test specific hypotheses concerning the presence and origin of anomalously high concentrations of the elements. Results of the random sampling show that the different geologic formations have different characteristic trace element concentrations. The Whitsett Formation has higher molybdenum (resulting from minor near-surface mineralization) and lower copper concentrations than the other two formations. With the exception of molybdenum in the Whitsett Formation and copper in all three formations, the trace element concentrations are similar to published average concentrations in soils worldwide. Sampling in areas of mining and mineralization indicates that high concentrations of molybdenum, arsenic, or selenium occur dominantly in two situations: (1) in areas of shallow mineralization, resulting from natural processes, and (2) in drainages adjacent to older abandoned mines, resulting from runoff from the mines. Moderately high concentrations also occur in a few reclaimed areas. Windblown dust from mining areas has not measurably affected trace element concentrations in adjacent areas. Comparison of molybdenum and copper concentrations in soils and grasses and theoretical considerations of the availability to plants of molybdenum and copper in soils suggest that forage in much of the area studied could have anomalously low copper/molybdenum ratios-low enough to induce molybdenosis in cattle.
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    Proceedings Gulf Coast Lignite Conference: Geology, Utilization, and Environmental Aspects
    (University of Texas at Austin. Bureau of Economic Geology, 1978) Kaiser, W.R.
    Papers in this volume were presented at the Gulf Coast Lignite Conference held in Austin, Texas, June 1976. Papers were edited, in some cases extensively, and subjectively grouped by discipline, paralleling that of their presentation at the Conference.
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    Stratigraphy of Lower Cretaceous Trinity Deposits of Central Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1971) Stricklin, Jr., F.L.; Smith, C.I.; Lozo, F.E.
    The stratigraphic record of the Lower Cretaceous Trinity Division in Central Texas, as revealed by extensive outcrop investigation, is that of a shallow sea transgressing the southern flank of the ancient Llano Uplift. This history is demonstrated by the overlap of marine carbonates on terrigenous facies representative of nearshore or onshore deposition and by sedimentary features indicative of various shallow-water environments of the marine shelf. Internally, the Trinity is comprised of three elastic-carbonate couplets, separated by disconformities, that reflect a pattern of cyclic sedimentation superimposed on the overall transgressive regimen. These couplets, made up of terrigenous formations overlain by carbonate formations, are regarded as lithogenetic time-stratigraphic units and are designated lower, middle, and upper Trinity. Formations constituting these Trinity subdivisions are, in ascending order of deposition, Sycamore Sand and Sligo Limestone, Hammett Shale and Cow Creek Limestone, and Hensel Sand and Glen Rose Limestone. Trinity deposits are particularly illuminating from an environmental point of view because features of stratification and sedimentation are exposed in unusual detail. Included among the environmentally diverse strata are blanket-like beach deposits, rudist reefs, widespread tidal-flat deposits, shallow-water evaporites with an association of unusual diagenetic features, and shore deposits of caliche and alluvium. Of these strata, the beach and tidal-flat deposits are of prime importance because (1) they illustrate the diversity of environmental conditions that existed on the marine shelf, and (2) certain of their features allow interpretations of water depth, degree of water circulation, and morphology of the depositional environment. The formations, bedding sequences, and sedimentary features that are genetically associated with these deposits should aid in the recognition of similar deposits elsewhere. Among the numerous sedimentary features that have proved valuable in the recognition of Trinity depositional environments are sequences of cross-bedding, ripple marks, and organic features distributed along bedding surfaces. The latter include stromatolitic mounds and ridges of algal origin, clam borings, levels of bored pebbles, dinosaur tracks, mudcracks, and oyster shells cemented in growth position to bedding surfaces. If these features occur in a succession of marine beds, they indicate shallow-water, probably intertidal, deposition, and the surfaces bored by clams and incrusted by oyster shells are very likely related to brief subaerial exposure of marine substrates and consequent hardening of sediments. On the other hand, if such borings and incrustations occur on top of continental sediments, they are associated with a disconformity and mark a former land surface transgressed by the sea. The overall character of the Trinity and the nature of the land over which the transgression occurred indicate that a mild degree of land erosion favored the extensive deposition of low-to-high-energy bioclastic limestones along a shore of hummocky relief. This differs markedly from the setting of the modern low-lying Gulf Coastal Plain and its deposits. Except in some areas of very low land relief, such as along the Florida peninsula, the shelf today is being veneered predominantly by land-derived sediments.
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    Environmental Geology of the Austin Area: An Aid to Urban Planning
    (University of Texas at Austin. Bureau of Economic Geology, 1976) Garner, L.E.; Young, K.P.
    The area described in this report comprises 712 square miles centered on the City of Austin. The area extends north almost to Round Rock, south to the vicinity of Buda, east to just beyond Manor, and west to about 5 miles west of Oak Hill. It includes approximately 604 square miles of Travis County, 38 square miles of Hays County, 18 square miles of Bastrop County, and 52 square miles of Williamson County. The aim of this publication is to supply geologic information that can be used to prevent or minimize problems that arise during urban development. A series of maps has been constructed for this purpose; the maps illustrate distribution of topographic conditions, soils, surface drainage, physical properties, rock types, land use, and vegetation. Base maps were compiled from 7.5- and 15-minute U. S. Geological Survey topographic maps and a 1970 edition of a map of the City of Austin. Basic geologic mapping was completed on aerial photographs at a scale of 1:20,000. Supplementary maps were prepared by combining data from the basic geologic map with soils, engineering, topographic, and vegetation data. Final maps were constructed at scales of 1:62,500 (approximately 1 inch equals 1 mile) and 1:125,000 (approximately 1 inch equals 2 miles).
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    Geology of the Barrilla Mountains, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1950-12) Eifler, Jr., G.K.
    The Barrilla Mountains, in the northeastern part of the Davis Mountains of Trans-Pecos Texas, are composed of Tertiary volcanic materials. Five tuffs and five lava flows, 1500 feet thick occurring throughout the mountains, persist in thickness and lithologic characteristics. Their upper surfaces show little erosion. The lavas are chiefly Silicic and soda rich. The volcanic succession is underlain by a Tertiary sandstone above Upper Cretaceous marine formations. These were slightly deformed by the Laramide revolution, subsequently beveled, and everywhere covered by the sands of coalescing streams. The sandstone contains well-rounded chert and quartzite pebbles. Broad folds and normal faults succeeded the extrusions of the youngest lava.
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    Texas Miners Boost Talc Output
    (University of Texas at Austin. Bureau of Economic Geology, 1958-02) Flawn, Peter T.
    Texas' Hudspeth County talc mining, begun in 1952 when Southwestern Talc Corp. carried out pioneer exploratory operations, has expanded during the last five years and can today claim six active operations. These Include (1) Southwestern Talc Corp., Llano, Texas, (2) West Texas Talc Corp. (properties sold to the Milwhite Co., Inc., Houston, in October 1957), (3) Texas Talc Co., a subsidiary of Dallas Ceramic Tile Co., (4) Lone Star Mining Co., subsidiary of Royal Tile Manufacturing Co., Fort Worth, (5) Southern Clay Products Co., also known as Christian & Sons, Gonzales, Tex., (6) Glenn- Ray Corp., (Georgia Talc Co., Chatsworth Georgia, operator). Deposits occur within the Precambrian Allamoore formation in an area about 20 miles long in an east-west direction and 5 miles wide in a north-south direction. The Allamoore is a highly deformed and variably metamorphosed sequence of interlayered limestone and volcanic rocks, including thin beds of phyllite. The phyllite is commonly talcose the amount of siliceous and calcareous impurities within the talc bodies shows wide variations. Phyllite units are mostly steeply dipping layers with a maximum thickness of about 200 or 300 ft which pinch and swell for a strike distance of up to several thousand feet. At Rossman mine (see map), two talc bodies occur as nearly vertical beds enclosed by cherty limestone members of the Allamoore formation. Except in the immediate vicinity of the talc, these limestones do not appear to be appreciably dolomitic. The main body is a tabular wedge-shaped unit about 7,000 ft long; it strikes about east-west, dips 70 degrees to 85 degrees south, and tapers from a width of 400 to 500 ft on the west to 100 to 200 ft on the east where it is cut off by a thrust fault. Talc is in contact with a small mass of diabase of uncertain age at orebody's west end. [The] problem of talc's origin has not yet been solved. The Allamoore formation is composed mainly of interlayered cherty limestone and volcanic rocks, and beds of cherty carbonate rock are known to occur within bodies of talc. Pinching and swelling beds of foliated talc are concordant in the sedimentary sequence and show little variation over a strike distance of about 20 miles. There is no indication of origin through hydrothermal alteration of basic igneous rock either in the shape of the bodies or in the form of unaltered relicts. Detailed study of the talc bodies is necessary for a conclusive statement on their origin, but information available to date [1958] suggests an origin through alteration of sedimentary or pyroclastic rocks such as dolomitic marl or magnesium-rich tuff.
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    Potential Low-Grade Iron Ore and Hydraulic-Fracturing Sand in Cambrian Sandstones, Northwestern Llano Region, Texas
    (University of Texas at Austin. Bureau of Economic Geology, 1964-08) Barnes, Virgil E.; Schofield, Daniel A.
    The red upper unit of the Hickory Sandstone is a hematitic and goethitic sandstone containing a large reserve of potential low-grade iron ore. It is estimated that about 7 million long tons of elemental iron is locked up in each square mile of the upper 30 feet of this deposit in sandstone averaging about 12.4 percent elemental iron. At least 175 square miles of the deposit is under less than 800 feet of cover, and reserves in the upper 30 feet in this area total about 650 million long tons if 75 percent of the potential iron ore is minable and two-thirds of the iron in the mined ore is recoverable. Beneath this level another 50 or 60 feet of poorly exposed iron-bearing sandstone is probably equally as iron-rich, and if this is true, total potential reserves may be as much as 1.6 billion long tons of elemental iron in 23 billion long tons of rock or about 6 billion tons of concentrates. No part of the deposit can be regarded as direct shipping ore. Iron oxide from the red unit of the Hickory Sandstone, except for high carbonate mineral content, is of paint pigment quality. Hydraulic-fracturing sand production from the lower unit of the Hickory Sandstone is well established in the Voca area, McCulloch County, and within the area of this report the amount of such sand is very large. The middle unit of the Hickory Sandstone, the Lion Mountain Sandstone, the Welge Sandstone, and the sandstone zones in the San Saba Member appear to be devoid of deposits of value.
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    Land Capability in the Lake Travis Vicinity, Texas A Practical Guide for the Use of Geologic and Engineering Data
    (University of Texas at Austin. Bureau of Economic Geology, 1975) Woodruff, Jr., C. M.
    The Lake Travis vicinity lies predominantly within a carbonate rock terrane and is the site of ongoing intensive residential development. Such development may impose adverse environmental effects such as upland erosion, rapid infilling of the lake with sediment, and the ultimate lowering of surface- or ground-water quality. Furthermore, inhabitants may be subjected unwittingly to geologic hazards such as flooding or mass wasting. These adversities can be largely avoided if the natural carrying capacity of the land is assessed and if human activities accordingly compensate for these limitations. A series of maps shows the facets of the land needed to evaluate the natural capabilities for sustaining various human uses of lakeshore lands. The basic maps show topography, physical properties (of substrate), and environmental geology (which is an integration of processes, substrate, and landforms). These maps and tabular interpretations facilitate judgments regarding engineering-construction feasibility, long-term ground stability, loci of hazards, water regimes, mineral resource localities, and characteristics of biotic and engineering soils. These judgments are further facilitated by a series of simplified maps showing soil distribution, thickness, and texture, fracture-trace intensity, and ground slope. Areas subject to ongoing hazardous processes pose the most severe constraints on human activities. These include flood-prone areas and unstable-slope areas. Flood-prone areas consist of land below lake-spillway level and areas adjacent to lake tributaries. Unstable-slope areas generally comprise oversteepened claystone terranes. Most of the carbonate rock terrane is covered by thin soils, so that constraints on uses depend mainly on ground-slope characteristics, properties of substrate, or the possibility of ground-water recharge and storage. High-slope areas pose problems with rapid surface-water runoff and resurfacing of septic effluents as well as construction difficulties related to grading and excavating. The low-slope carbonate rock areas may pose construction difficulties related to a well-indurated substrate. Also, in these gently sloping areas there is the possibility of recharge of septic effluents into local ground-water supplies. Claystone terranes constrain uses mainly because of substrate-soil properties of relatively low strength and low permeability. However, these properties offer possibilities in terms of potential solid waste disposal sites. Areas underlain by friable sand and conglomerate and alluvium impose fewer constraints on uses. Soils are generally thicker and slopes are commonly more gentle in these areas than in the carbonate rock terranes. However, uses such as intensive residential developments with septic tanks or solid waste emplacement are largely precluded because of local high substrate permeability and a shallow water table. Constraints on human uses and activities refer to constraints regarding the land in a natural condition. In most instances the constraints can be mitigated by modification of the land or by adjustment of the proposed activities so that uses may not be, in fact, precluded.