Geological Circulars

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Peer-reviewed geoscience research summaries, targeted on Bureau project areas in Texas and other locations, 1965–2003.

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Oakwood salt dome, east Texas: geologic framework, growth history, and hydrocarbon production
(University of Texas at Austin. Bureau of Economic Geology, 1983) Giles, Alice Burns; Wood, Debra H.
The top of mushroom-shaped Oakwood salt dome is approximately 210 m (700 ft) beneath the boundary of Freestone and Leon Counties near the southwestern end of the East Texas Basin, The dome is surrounded by Jurassic, Cretaceous, and lower Tertiary marine and nonrnarine strata. A salt pillow initially formed in Late Jurassic "Smackover" time, when faulting contributed to uneven sediment loading of the Louann Salt. The dome began to grow vertically into a diapiric configuration during the deposition of Upper Jurassic - Lower Cretaceous clastics (Bossier - Travis Peak Formations) and probably remained near the depositional surface during most of its growth, The estimated average vertical rise of the top of salt at Oakwood salt dome shows a general decrease over time, from approximately 0.07 mm/yr 9230 ft/m.y.) during Early Cretaceous time to 0.002 mm/yr (5 ft/m.y.) since early Tertiary (Reklaw) time. Hydrocarbons are produced from Woodbine sediments beneath the dome's overhang.
Virgil and lower Wolfcamp repetitive environments and the depositional model, North-central Texas
(University of Texas at Austin. Bureau of Economic Geology, 1969) Brown, L. F. (Leonard Franklin), 1928-
Virgil and lower Wolfcamp rocks on the Eastern Shelf in North-central Texas are composed of several intergradational depositional systems comprising 1,200 to 1,500 feet of off-lapping, predominantly terrigenous sediments. At least a dozen major and numerous minor repetitive sequences consist of superposed deposittional systems, composed of more or less homotaxial component facies. Rapidly shifting fluvial-delta sites and associated interdeltaic and open shelf environments on the slowly subsiding shelf were subjected to marine destruction, mud compaction subsidence, and marine transgression. Variations of the basic sequence in time and space resulted from shifting depositional systems. Pluvial variants are downslopes, and deltaic and interdeltaic variants are concentrated in intermediate areas. These facies tracts shifted irregularly southwestward during Virgil and Wolfcamp deposition as the average strandline migrated with westward shelf progradation. Westward pointing deltas locally extended subaerial environments far downslope. Delta sequences between bases of successive delta systems are diachronous and aperiodic as deltation irregularly reoccupied former delta sites. Sequences between bases of successive transgressive limestone facies are also interpreted to be aperiodic and diachronous, but bounding limestones display regional continuity. Delta and fluvial constructional facies represent relatively brief, discrete time intervals, while destructional, interdeltaic, and transgressive facies involved greater time resulting in complex chronology within sequences. The fluvial-deltaic model for Virgil and Lower Wolfcamp rocks make it unnecessary to invoke external cyclic control to explain these North-central Texas deposits. The self-regulating model can operate under continuous sediment supply and continuous but slow shelf subsidence. The model is based on fades relationships and processes rather than absolute scale and geometrical comparison with Recent models. The diachronous nature of fades required by the model and supported by stratigraphic evidence indicates that repetitive deposition was primarily governed by sedimentary processes active within the local basin.
Geology and geohydrology of the Palo Duro Basin, Texas panhandle: a report on the progress of nuclear waste isolation feasibility studies (1981)
(University of Texas at Austin. Bureau of Economic Geology, 1982) Gustavson, Thomas C.
Integrated study of the basin structure, tectonic history, rock physics, physical stratigraphy, hydrogeology, geochemistry, natural resources, and geomorphology of the Palo Duro and Dalhart Basins in the Texas Panhandle is part of a national evaluation of ancient salt basins as potential sites for isolation and management of nuclear wastes. Since early 1977, the Bureau of Economic Geology has been evaluating several salt-bearing basins within the State of Texas as part of the national nuclear waste repository program. The Bureau, a research unit of The University of Texas at Austin, is conducting a long-term program to gather and interpret all geologic and hydrologic information necessary for description, delineation, and evaluation of salt-bearing and related strata in the Palo Duro and Dalhart Basins of the Texas Panhandle. The program in fiscal year (FY) 81 was divided into five broad research tasks, which were addressed by a surficial analysis and shallow stratigraphy group, a hydrology and geochemistry group, a basin analysis group, a host-rock analysis group, and a seismicity and tectonic environment group (fig. 1). The surficial analysis and shallow stratigraphy group has collected remotely sensed, surface and subsurface data to describe salt dissolution, surface processes, and rates and styles of geomorphic development. The hydrology and geochemistry group continued analysis of shallow and deep fluid circulation within the basins and rock and fluid geochemistry within the salt-bearing and other stratigraphic units. The basin analysis group characterized the major salt-bearing stratigraphic units within the basins, assessed the potential for generating and trapping hydrocarbons within the basins, and initiated studies of salt quality. Concurrently, the host-rock analysis group continued a study of cores from several drilling sites for analysis salt and other lithologic units within the cores. The seismicity and tectonic environment group continued studies of regional gravity, deep-basement structure and tectonic development of the basin, and structural controls of sedimentation and analyzed surface fracture systems. This report, a summary of progress during FY81, presents principal conclusions and reviews methods used and types of data and maps generated. Topical reports, discussing in detail various geological aspects of the Palo Duro and Dalhart Basins, are being published as phases of the study are completed. This research was supported by the U.S. Department of Energy and its predecessor, the Energy Research and Development Administration, under contracts numbered EY-77-S-05-5466 (FY 78), DE-AC97-79ET44614 (FY791, and DE-AC97-80ET46615 (FY 80 and FY 81).
Uranium in Texas, 1967
(University of Texas at Austin. Bureau of Economic Geology, 1967) Flawn, Peter Tyrell
The uranium industry, born in boom in the late 1940's and early 1950's, fell upon hard times after about a decade of lusty growth as anticipated private markets failed to develop on schedule and the United States Atomic Energy Commission cut back and stretched out its purchase program. Exploration for uranium in the United States came to a halt. Mills closed down or operated on reduced schedules as contracts expired. But in 1965 there were signs of change as more and more announcements of construction of nuclear reactors for generation of electric power appeared in the newspapers, and by 1966, the discouraged uranium salesman found doors opening rapidly and smiles on the faces of his potential customers. The hoped-for private-sector market for uranium had become a reality. By September 1, 1966, a total of 47 reactors were either in operation, under construction, or firmly committed in the United States; of the total, orders for or commitments for 32 were made since February of 1965. The industry considered this sharply rising curve, looked at the nuclear fuel requirements, appraised the known reserves of uranium ore, and literally sprang into action. In the first half of 1966, only about half a million feet of exploratory drilling was completed; twice this was scheduled for the second half of the year and a million and a half feet has been budgeted for 1967.
Hydrocarbon accumulation patterns in the East Texas salt dome province
(University of Texas at Austin. Bureau of Economic Geology, 1982) Wood, Debra H.; Giles, Alice Burns
Mobilization of the Louann Salt created the present structural configuration in the central part of the East Texas Basin and was the major control on hydrocarbon accumulation in the area. Salt-cored anticlines, turtle-structure anticlines, and salt diapirs were produced by flow of salt. Of these, the most prolific oil- and gas-producing structures have been anticlines with deep salt cores. These deep-seated salt domes uplifted thick stratigraphic sections; thus, their crestal anticlines are multiple-zoned productive structures. Turtle-structure anticlines are less important as hydrocarbon traps. Low productivity of turtle-structure anticlines compared with salt-cored anticlines may result from later development of turtle structures and from uplift of a relatively thinner stratigraphic section. Production associated with shallow salt domes has been relatively minor. If a large amount of oil or gas accumulated over the early pillow forms of these diapirs, then much of it may have leaked along faults associated with dome growth or been caused by erosional breaching of reservoirs over the dome crest after uplift. Deeper exploration of each type of structure (salt-cored anticlines, turtle-structure anticlines, and shallow salt domes) may be productive to the oil and gas companies. Shallow salt domes in East Texas have been evaluated as repositories for isolation of nuclear waste. A suitable site must not harbor natural resources that might attract interest and lead to future breaching of the repository. Substantial hydrocarbon accumulations have not been discovered at most of the shallow domes in East Texas. However, these domes have attracted much drilling activity primarily because of highly successful exploration of shallow salt domes in the Gulf Coast Basin.
Depositional systems and oil-gas reservoirs in the Queen City Formation (Eocene), Texas
(University of Texas at Austin. Bureau of Economic Geology, 1972) Guevara, Edgar H.; García, Roberto
Regional surface and subsurface studies indicate that thick deltaic (Queen City Formation) and thin shelf (Reklaw and Weches Formations) sequences compose the stratigraphic interval between the top of the Carrizo Sand and the base of the Sparta Formation. In East Texas, the Queen City Formation accumulated as part of a high-constructive, lobate delta system; and in South Texas, as part of a high-destructive, wave-dominated delta system. In South Texas, principal facies are meanderbelt sand, lagoonal mud, stacked coastal barriers, and prodelta shelf mud facies. In East Texas, delta plain, delta front, and prodelta facies are dominant; and in Central Texas, the principal facies are strandplain sands originated by southwestward longshore drift of sediments from the high-constructive delta system. Facies distribution, composition, and size of the deltas in East Texas are similar to lobes of the Holocene high-constructive Mississippi delta system and to ancient deltas in the lower part of the Wilcox and m the Jackson Groups of the Gulf Coast Basin. Deltaic sediments of South Texas are comparable to Pleistocene high-destructive, wave-dominated facies on the Surinam coast, to the Holocene Rhone delta system, and to ancient deltas in the upper part of the Wilcox Group. Queen City deltas prograded gulfward over shelf muds and glauconites of the Reklaw Formation; they are overlain by comparable shelf facies of the Weches Formation. In East Texas, deltaic facies wedge out eastward. Terrigenous elastics of the high-destructive deltas extend southward into Mexico. Hydrocarbons are produced from thin strike-oriented sands downdip from the belt of maximum sand thickness of the high-destructive deltas in South Texas; only a minor amount of oil and gas has been obtained from delta front and distributary channel sands of the high-constructive deltas in East Texas.
Fault tectonics of the East Texas Basin
(University of Texas at Austin. Bureau of Economic Geology, 1982) Jackson, M. P. A.
Principal fault systems in the East Texas Basin were examined in terms of their distribution, geometry, displacement history, and possible origins. All the faults studied are normal and moved syndepositionally over approximately 120 Ma (million years); some have listric shapes and associated rollover anticlines. The faults formed by processes associated with gravitationally induced creep of the Louann Salt, such as gliding over a salt decollement zone, crestal extension and collapse over salt pillows and turtle structures, and salt withdrawal from beneath downthrown blocks. None of the fault zones were caused by marginal flexure of the basins or salt diapirism; there is little evidence of basement control. Paucity of data prevents a reliable interpretation of the Mount Enterprise Fault, but our data suggest that none of the fault zones in this basin pose a seismic threat to a hypothetical nuclear-waste repository in the Gulf Coast area.
Impact of evaporite dissolution and collapse on highways, and other cultural features in the Texas Panhandle and eastern New Mexico
(University of Texas at Austin. Bureau of Economic Geology, 1981) Simpkins, William W.; Gustavson, Thomas C.; Alhades, A.B.; Hoadley, A.D.
Geological investigations in the Texas Panhandle and eastern New Mexico indicate that regional subsurface dissolution of Permian evaporites has occurred and is an ongoing process. Evidence of removal of large volumes of evaporites (mainly halite) and collapse of overlying beds is demonstrated by cross sections constructed from gamma-ray logs. Surface manifestation of subsurface dissolution and collapse is clearly shown in Hall County, Texas, where over 400 sinkholes and undrained depressions have been identified from aerial photographs. Sinkhole diameters up to approximately 100 m (300 ft) and depths to 15 m (50 ft) have been observed. Eleven active northeast- and southwest-trending fractures and faults have been recognized, some of which are demonstrated as patched sections of highways. Formation of collapse features and faults that damage highways is a recognized problem in the region. Stock tanks and large reservoirs are also affected to a lesser degree. Dissolution and collapse pose difficult problems for geologists, highway engineers, and maintenance crews. Areas of active subsurface dissolution have been identified, but development of collapse features and faults at the surface generally follows no predictable pattern. The history of, and potential for, evaporite dissolution should be investigated in each area before construction of highways, reservoirs, and stock tanks. Areas with high densities of collapse features, fractures, and faults should be avoided when possible.
Lineament analysis and inference of geologic structure: examples from the Balcones Ouachita trend of Texas
(University of Texas at Austin. Bureau of Economic Geology, 1982) Caran, S. Christopher; Woodruff, C. M.; Thompson, Eric J.
Lineaments perceived in remotely sensed images are reliable indicators of geologic structure. Lineaments on ten Landsat multispectral scanner images (band 5; 1:250,000 scale) were mapped covering the Ouachita/Balcones-Luling-Mexia-Talco structural trend between the Rio Grande and Red river in Texas. More than 5,000 lineaments were perceived in these images. Maps depicting the lineaments (individually and in various combinations) were compared with maps of structural/ tectonic features and geothermal gradient contours, noting instances of apparent correlation among these themes. Lineaments are correlative with the individual faults and the aggregate fault patterns of the Baicones, Luling, Mexia, and Talco fault zones, Transverse lineaments, which trend almost perpendicular to these fault zones, mark the northernmost extent of the Balcones fault system and outline carbonate piatforms, such as the Belton High/Moffat Mound trend and the San Marcos arch. Transverse lineaments are coincident also with the axes of the buried Chittim and Preston anticlines and with the flanks of the Sherman and Round Rock synclines. Numerous salt domes occur at depth in the western part of the east Texas basin near the trend; many of these domes, particularly those in Henderson, Anderson, and Freestone Counties, are found along and at the intersection of major lineament zones where the concentration of individuai lineaments is greatest. Most of the buried Late Crelaceocs volcanoes of central Texas near Austin lie along northeast southwest- trending lineament zones; the altered pyroclastic rocks and associated beachrock facies at many of these volcanoes are hydrocarbon reservoirs. The orientation and spacing of geothermal gradient contour lines ("isograds") also correspond to major structures and thus, to the pattern of lineaments throughout the region. Correlation of (1)individual lineaments, zones of cortiguous or nearly parallel lineaments, and areas of homogeneous lineament density and orientation to (2) surface and subsurface structure and (3) geothermal,'isograd" patterns indicates that lineament analysis has many potential applications to regional mineral resource assessment.
Lineament analysis based on Landsat imagery, Texas Panhandle
(University of Texas at Austin. Bureau of Economic Geology, 1981) Finley, Robert J.; Gustavson, Thomas C.
Analysis of seven frames of Landsat imagery covering the Texas Panhandle and adjacent areas revealed linear physiographic features including stream channels, stream valleys, scarps, and aligned playa-lake depressions. These lineaments show preferred orientations of 300°-320°, 030°-050°, and, 0°-020°. The 300°-320° orientation of aligned playas and shallow surface drainage is best developed on the surface of the Southern High Plains. The orthogonal 030°-050° orientation is less well represented. Lineaments oriented 0°-020° are most readily detected in the dissected terrain of the Roiling Plains in the eastern Texas Panhandle; a secondary orthogonal trend oriented 270°-280° is also present. Lineament orientations are similar to orientations of joints measured in the field and to regional structural trends, which suggests that development of physiographic lineaments is controlled or influenced by geologic structure. Few surface faults are mapped in the region; therefore, joints rather than widespread faults are a likely structural geologic control, Joints may provide paths of weakness along which surface drainage might develop preferentially. Joint intersections provide potential sites for downward percolation of water, possibly enhancing playa development, as suggested by dissolution of caliche beneath playas. Thus, joints probably exert an important control on the geomorphology of the region.
Geology and geohydrology of the Palo Duro Basin, Texas panhandle: a report on the progress of nuclear waste isolation feasibility studies (1980): annual report for period October 1, 1979-September 30, 1980
(University of Texas at Austin. Bureau of Economic Geology, 1981) Gustavson, Thomas C.
Integrated study of the basin structure, tectonic history, physical stratigraphy, hydrogeology, geochemistry, geomorphology, natural resources, and rock physics of the Palo Duro and Dalhart Basins in the Texas Panhandle is part of a national evaluation of ancient salt basins as potential sites for isolation and management of nuclear wastes. Since early 1973, the Bureau of Economic Geology has been evaluating several salt-bearing basins within the State of Texas as part of the national nuclear repository program. The Bureau, a research unit of The University of Texas and the State of Texas, is conducting a long-term program to gather and interpret all geologic and hydrologic information necessary for description, delineation, and evaluation of salt-bearing and related strata in the Palo Duro and Dalhart Basins of the Texas Panhandle. The program in FY80 was divided into five broad research tasks, which were addressed by a surficial analysis and shallow stratigraphy group, a hydrology and geochemistry group, a basin analysis group, a host-rock analysis group, and a seisrnicity and tectonic environment group. The surficial analysis and shallow stratigraphy group has collected remotely sensed, surface and subsurface data to describe land resources, surface processes, and rates and styles of geomorphic development. The hydrology and geochemistry group has continued analysis and shallow and deep fluid circulation within the basins and has initiated studies of rock and fluid geochemistry within the salt-bearing units. The basin analysis group has characterized the major salt-bearing stratigraphic units within the basins and has assessed the potential for generating and trapping hydrocarbons within the basins. Concurrently, the host-rock analysis group has continued a study of cores from two drilling sites for analysis of salt and other lithologic units within the cores. The newly formed seismicity and tectonic environment group has initiated studies of deep-basement structure and tectonic development of the basin and has made an analysis of surface fracture systems. This paper, a summary of progress during FY80, presents principal conclusions and reviews methods used and types of data and maps generated. Topical reports, discussing various geological aspects of the Palo Duro and Dalhart Basins in detail, are being published as phases of the study are completed. This research was supported by the Department of Energy and its predecessor, the Energy Research and Development Administration, under contracts numbered EY-77-S-05-5466 (FY78), DE-AC97-79ET446 14 (FY79), and DE-AC97-ET46615 (FY80).
A preliminary assessment of the geologic setting, hydrology, and geochemistry of the Hueco Tanks geothermal area, Texas and New Mexico
(University of Texas at Austin. Bureau of Economic Geology, 1981) Henry, Christopher D.; Gluck, James K.
The Hueco Tanks geothermal area contains five known but now inactive hot wells (50° to 71°C). The area trends north-south along the east side of Tularosa-Hueco Bolson astride the Texas-New Mexico border approximately 40 km northeast of El Paso. Because of its proximity to El Paso, geothermal water in the Hueco Tanks area could be a significant resource. Hueco Bolson is an asymmetric graben. Greatest displacement along boundary faults is on the west side adjacent to the Franklin Mountains. Faults, probably with less displacement, also form an irregular boundary on the east side of the bolson. Several probable faults may allow the rise of thermal waters from depth. Ground water in the central part of Hueco Bolson flows southward to the Rio Grande. However, four of the five hot wells occur in a ground-water trough along the eastern margin of the bolson. The trough may be bounded by one of the postulated faults serving as a barrier to ground-water flow. Data on permeability of potential reservoir rocks, including basin fill and fractured bedrock, suggest that they may be sufficiently permeable for development of geothermal water. The concentration of dissolved solids in the geothermal waters varies from 1,100 to at least 12,500 mg/L, but most waters show high concentrations. They are Na-Cl-(SO4) waters similar in composition to nonthermal waters in basin fill. The composition probably results from contact with evaporite deposits either in basin fill or in Paleozoic bedrock. Shallow reservoirs reach maximum temperatures of about 80° to 110°C. Available data are too limited to evaluate adequately the resource potential of geothermal water in the Hueco Tanks area. A complete exploration program, including geological, hydrological, and geochemical investigation, is recommended.
Evaluation of sanitary landfill sites, Texas coastal zone: geologic and engineering criteria
(University of Texas at Austin. Bureau of Economic Geology, 1972) Brown, L. F. (Leonard Franklin), 1928-; Fisher, W. L. (William Lawrence), 1932-; Malina, Joseph F., 1935-
Basic geologic, hydrologic and engineering criteria on which selection of sanitary landfill sites should be based include (1) thickness, excavation characteristics, permeability, solution-holding capacity, and reactivity of host and cover materials; (2) hydrologic properties including depth to water table, season variation in position of water table, and rate of liquid movement; and (3) nature of terrain in terms of slope, topography, and surface drainage. Evaluation of these features must be based initially on adequate mapping and inventory of surface and near-surface earth materials-both bedrock and surficial soils. Solid wastes include a broad spectrum of residues of municipal and industrial activities. These waste solids include refuse from residential areas, sludges from water and wastewater treatment, plant trash, organic and inorganic chemicals, toxic materials, manures, oils, and other materials which are not discharged into surface waters or into the atmosphere. Basic environmental mapping recently completed in an 18,000-square-mile area of the Texas Coastal Zone, an area embracing nearly one-third of the State's population and industry, shows the distribution of 130 substrate and landform map units. Map units are grouped into four main landfill suitability groups. Of these groups, only one is entirely suitable for landfill sites, two constitute very poor site areas, and one can be utilized only locally and with proper engineering design. Principal landfill suitability groups in the Texas Coastal Zone include (1) clays and muds with low permeability, high water-holding capacity, high compressibility, high to very high shrink-swell potential, low internal drainage, level to depressed surface relief, low shear strength, and high plasticity-such clays and muds provide secure landfill sites; (2) sands with high to very high permeability, low water-holding capacity, low compressibility, low shrink-swell potential, high internal drainage, high shear strength, and low plasticity-these sands are very poor landfill sites; (3) wetlands (marshes and swamps) with very low permeability, high water-holding capacity, high to very high compressibility, high shrink-swell potential, very poor internal drainage, depressed surface relief, and permanently high water table - these wetlands are poor landfill sites; and (4) clayey sands and silts with moderate to low permeability, moderate water-holding capacity, moderate compressibility, low to moderate shrink-swell potential, moderate internal drainage, and high shear strength - these sands and silts are marginal for solid-waste disposal but can be used locally with proper engineering design and control. Of the approximately 100 in-ground solid-waste disposal sites currently in operation in the Texas Coastal Zone, only 20 percent are geologically and hydrologically secure sites. Thirty percent are in substrates that are insecure, potential or active pollution areas. The remaining 50 percent of the sites occur within highly marginal areas with at least some degree of active or potential pollution. Clearly, geologic and hydrologic criteria have not been used in the selection of most existing sites. The Texas Coastal Zone is not unique; in far too few landfill areas are adequate geologic and land-suitability maps available to the planner. Within the Texas Coastal Zone and in most other areas, immediate economic considerations outweigh fundamental geologic and hydrologic suitability in site selection. For example, in the heavily populated and industrialized upper Texas Coastal Zone, the most secure and suitable substrates for solid-waste disposal also support the most valuable agricultural lands; by contrast, geologically and hydrologically insecure sites, such as wetlands and permeable sands, generally constitute less expensive land. Abandoned sand and gravel pits, for example, provide inexpensive, generally available, and ready-made sites, yet due to high substrate permeability, extensive pollution can result when these abandoned pits are used as solid-waste disposal sites. As in most other areas, the bulk of solid waste in the Texas Coastal Zone is disposed of in open dumps; only a small part of the total solid waste is incinerated or disposed of in a sanitary landfill. Under present conditions, properly managed landfills provide the most adequate manner of waste disposal and are naturally far superior to open dumps. However, unless selection of the site is based on geologic and hydrologic criteria, sanitary engineers will be severely handicapped in their efforts to prevent unacceptable environmental pollution.
Cretaceous paleogeography: implications of endemic ammonite faunas
(University of Texas at Austin. Bureau of Economic Geology, 1972) Young, Keith, 1918-2004
Endemic ammonite faunas evolved from cosmopolitan faunas in a series of successive episodes over about 35 million years of the Cretaceous of the Gulf Coast of the United States. During basin-basin-margin tectonic adjustments the Cretaceous barrier reef was inundated or circumvented so that a cosmopolitan fauna entered the back-reef area. Gradual isolation of the fauna behind the barrier produced endemism. With the next basin adjustment the endemic fauna became extinct, and a new cosmopolitan fauna migrated into the back-reef area, likewise evolving into an endemic fauna in its turn. Six cosmopolitan-endemic cycles have been identified. Geological evidence suggests two or three additional cycles.
Calderas and mineralization: volcanic geology and mineralization in the Chinati Caldera complex, trans-Pecos Texas
(University of Texas at Austin. Bureau of Economic Geology, 1981) Duex, Timothy W.; Henry, Christopher D.
This report describes preliminary results of an ongoing study of the volcanic stratigraphy, caldera activity, and known and potential mineralization of the Chinati Mountains area of Trans-Pecos Texas. Many ore deposits are spatially associated with calderas and other volcanic centers. A genetic relationship between calderas and base and precious metal mineralization has been proposed by some (Albers and Kleinhampl, 1970) and denied by others (McKee, 1976, 1979). Steven and others (1974) have demonstrated that calderas provide an important setting for mineralization in the San Juan volcanic field of Colorado. Mineralization is not found in all calderas but is apparently restricted to calderas that had complex, post-subsidence igneous activity. A comparison of volcanic setting, volcanic history, caldera evolution, and evidence of mineralization in Trans-Pecos to those of the San Juan volcanic field, a major mineral producer, indicates that Trans-Pecos Texas also could be an important mineralized region. The Chinati caldera complex in Trans-Pecos Texas contains at least two calderas that have had considerable postsubsidence activity and that display large areas of hydrothermal alteration and mineralization. Abundant prospects in Trans-Pecos and numerous producing mines immediately south of the Trans-Pecos volcanic field in Mexico are additional evidence that ore-grade deposits could occur in Texas.
Geology and geohydrology of the East Texas basin: a report on the progress of nuclear waste isolation feasibility studies (1979)
(University of Texas at Austin. Bureau of Economic Geology, 1980) Kreitler, Charles W.; Agagu, Olusegun Kokumo, 1948-; Basciano, Joyce M.; Collins, Edward W.
Analysis during the second year was highlighted by a historical characterization of East Texas Basin infilling, the development of a model to explain the growth history of the domes, the continued studies of the Quaternary in East Texas, and a better understanding of the near-dome and regional hydrology of the basin. Each advancement represents a part of the larger integrated program addressing the critical problems of geologic and hydrologic stabilities of salt domes in the East Texas Basin. During the second year of the East Texas salt dome studies, significant advances in understanding the hydrologic and geologic stabilities of salt domes were based on the acquisition of much new data. Among these new sources of data are (1) 400 km (250 mi) of seismic reflection data that are both regional and site specific, (2) gravity data for the East Texas Basin, (3) 20 shallow boreholes over Oakwood Dome, (4) 1 hydrologic test hole downdip from Oakwood Dome, and (5) a complete core of the anhydrite-gypsum cap rock over Gyp Hill Dome in South Texas. The acquisition of seismic, gravity, and electric log data provided new understanding of the sedimentary infilling of the East Texas Basin and how it caused salt migration and dome growth. Deposition of the Travis Peak-Schuler sediments caused the first differential loading of the underlying Louann Salt and the migration of the salt into anticlinal ridges. Subsequent clastic depocenters occurred laterally to Travis Peak depocenters and caused further migration of the salt into diapirs. The greater the sediment loading, the further the salt anticline advanced through Trusheim's (1960) growth sequence: pillow structure to immature diapir and finally to a mature diapir. Most domes in the basin can be placed within this dome growth sequence. Analysis of the Gyp Hill cap rock showed that the cap rock was the result of salt dome dissolution and the accumulation of the insoluble residuum, anhydrite. Work completed on the Carrizo-Wilcox aquifer, the major fresh-water aquifer in the basin, shows that this aquifer has the greatest potential for causing dome dissolution leading to radionuclide transport. Ground-water circulation is controlled primarily by topography and structure. Fluid movement is generally downward because of the structural dip and leakage from overlying units. Chemical composition of the water evolves from a low-pH, oxidizing, calcium bicarbonate water in the outcrop to a high-pH, reducing, sodium bicarbonate water deeper in the aquifer. This chemical change has important implications for radionuclide transport.
Petroleum source rock potential and thermal maturity: Palo Duro Basin, Texas
(University of Texas at Austin. Bureau of Economic Geology, 1980) Dutton, S. P.
Samples collected from 20 geographically widespread wells in the sparsely drilled Palo Duro Basin were analyzed for total organic carbon content (TOC). Highest values of TOC, up to 6.9 percent, occur in Upper Permian San Andres dolomite in the southern part of the basin. Pennsylvanian and Lower Permian (Wolfcampian) basinal shales contain up to 2.4 percent TOC and are fair to very good source rocks. Kerogen color and vitrinite reflectance, which indicate maximum paleotemperatures, were analyzed in all samples containing greater than 0.5 percent TOC. Pennsylvanian and Wolfcampian kerogen is yellow orange to orange, an indication that temperatures were sufficiently high to begin to generate hydrocarbons from lipid-rich organic material. Palo Duro Basin samples have a broad range of vitrinite reflectance values, but populations with the lowest reflectance probably indicate the true temperatures that were reached in the basin. Average reflectance in representative Pennsylvanian vitrinite is 0.52 percent; in Wolfcampian samples the average reflectance is 0.48 percent. These values are consistent with kerogen color and suggest that basinal source rocks may have begun to generate hydrocarbons.
Facies patterns and depositional history of a Permian sabkha complex -- Red Cave Formation, Texas Panhandle
(University of Texas at Austin. Bureau of Economic Geology, 1980) Handford, C. Robertson; Fredericks, Paul E.
The Red Cave Formation (Permian, Leonard Series) in the Texas Panhandle consists of cyclic, red-bed clastic and carbonate-evaporite members that reflect deposition in extensive coastal sabkhas. These environments were bounded on the north by a desert wadi plain and on the south by a carbonate inner shelf that bordered the northern Midland Basin. Evaporite members were deposited in carbonate evaporite coastal sabkhas, and clastic members were deposited in mud-rich coastal to continental sabkhas that passed inland to wadi-plain environments. Inner shelf dolomites include slightly fossiliferous, faintly laminated to burrowed mudstone and pellet wackestone. These lithofacies are overlain by and interfinger northward with dolomite and anhydrite deposited in coastal sabkhas. Oolitic or pellet packstone and grainstone with well-developed cross-lamination suggest shallow subtidal to intertidal deposition. Supratidal facies include dolomitic mudstone with algal laminations and some intraclasts. Sabkha sequences are commonly capped with nodular anhydrite; mud-rich sabkha sequences culminate with red to green mudstone and anhydrite. Carbonate and evaporite facies pinch out generally toward the northwest and northeast into wadi-plain red beds. These facies include ripple-drift, cross-laminated siltstone and sandstone, adhesion-rippled siltstone, and red to green mudstone. Desiccation features, intraclasts, root zones, and paleosol horizons cap braided fluvial deposits and attest to subaerial exposure and probable non-marine conditions. Partial modern analogs to Red Cave sabkha depositional elements include coastal mud flats and alluvial fans in the northwestern Gulf of California, tidal flats and the Wooramel ephemeral stream delta in Gladstone Embayment, Shark Bay, Australia, and Trucial Coast sabkhas in the Persian Gulf. Each setting has certain facets that are remarkably similar to interpreted paleoenvironments and lithofacies of the Red Cave Formation.
Shoreline changes on Mustang Island and North Padre Island (Aransas Pass to Yarborough Pass): an analysis of historical changes of the Texas Gulf shoreline
(University of Texas at Austin. Bureau of Economic Geology, 1977) Morton, Robert A.; Pieper, Mary J.
Historical monitoring along Mustang and north Padre Islands records the nature and magnitude of changes in position of the shoreline and vegetation line and provides insight into the factors affecting those changes. Documentation of changes is accomplished by the compilation of shoreline and vegetation line position from topographic maps, aerial photographs, and coastal charts of various vintages. Comparison of shoreline position based on topographic charts (dated 1860-82) and aerial photographs (taken in 1937, 1956-60, 1969-70, and 1974-75) indicates short-term changes of accretion and erosion along the Gulf shoreline between Aransas Pass and Yarborough Pass. Erosion produces a net loss in land, whereas accretion produces a net gain in land. Comparison of the vegetation line based on, the aforementioned aerial photographs indicates short-term cycles of retreat related to storms (primarily hurricanes) and recovery during intervening years of low storm incidence. Long-term trend or direction of shoreline changes averaged over the 115-year time period of this study indicates that Mustang Island has experienced net erosion with two exceptions. Net accretion adjacent to Aransas Pass, which decreased from 1,600 feet near the south jetty to 350 feet about 2 miles south of the pass, was caused principally by inlet migration and concomitant outbuilding of the north end of the island prior to jetty construction in 1889. Net accretion also occurred about 1.5 miles north of the Nueces/Kleberg county line attendant with the infilling of Packery Channel. The remainder of Mustang Island recorded net erosion ranging from 75 to 350 feet and averaging 225 feet. Net rates of change, however, were low along Mustang Island except where net accretion ranged from approximately 3 feet per year to 14 feet per year. Net erosion on the island ranged from less than 1 foot per year to 3.8 feet per year and averaged 2.0 feet per year. Net changes on north Padre Island were predominantly accretionary; however, net erosion was recorded from Packery Channel southward for a distance of about 7 miles. Minimum net erosion was 50 feet, whereas maximum net erosion was 500 feet, and average net erosion was 220 feet. The shoreline from 6.5 to 9 miles north of the Kleberg/Kenedy county line experienced only minor net changes of 25 feet or less. The remaining shoreline of north Padre Island experienced net accretion ranging from less than 10 feet to 275 feet; net accretion, which increased southward along the island, averaged 140 feet. Net rates of change were also low along north Padre Island. Net erosion ranged from less than 1 foot to 5.4 feet per year and averaged 2.0 feet per year. Similarly, net accretion varied from less than 1 foot to 3.0 feet and averaged 1.5 feet per year. Because of limitations imposed by the technique used, rates of change are subordinate to trends or direction of change. Furthermore, values determined for long-term net changes should be used in context. The values for rates of net change are adequate for describing long-term trends; however, rates of short-term changes may be of greater magnitude than rates of long-term changes, particularly in areas where both accretion and erosion have occurred. Major and minor factors affecting shoreline changes include: (1) climate, (2) storm frequency and intensity, (3) local and eustatic sea-level conditions, (4) sediment budget, and (5) human activities. The major factors affecting shoreline changes along the Texas Coast, including Mustang and north Padre Islands, are relative sea-level conditions, compactional subsidence, and changes in sediment supply. Changes in position of the vegetation line are primarily related to storms. Studies indicate that changes in shoreline and vegetation line on Mustang and north Padre Islands are largely the result of natural processes, perhaps expedited by man's activities. A basic comprehension of these physical processes and their effects is requisite to avoid or minimize physical and economic losses associated with development and use of the coast.
Geochemistry of bottom sediments -- Matagorda Bay system, Texas
(University of Texas at Austin. Bureau of Economic Geology, 1979) McGowen, J. H.; Wilkinson, Bruce H., 1942-; Byrne, J. R.
Approximately 800 sediment samples from stream beds and bay bottoms of water bodies that compose the Matagorda Bay system were collected and analyzed. Shell-sand-mud ratios and total organic carbon content were determined, and 20 trace elements were detected. In general, highest concentrations of trace elements coincide with deep areas of- water bodies, areas of mud accumulation, and areas with high total organic carbon content. Zirconium, calcium, strontium, and mercury do not follow the distribution patterns of most other elements. Zirconium (Zr) is concentrated in sand located chiefly along bay margins and in tidal deltas; high Zr values result from the physical concentration of zircons as heavy mineral placers associated with sand bodies. Calcium and strontium distributions coincide with distribution of shell material. Mercury distribution is restricted to Lavaca Bay and northwestern Matagorda Bay. When concentrations of 20 trace metals in the Matagorda Bay system are compared with concentrations of elements in the crust, shale or clay, and seawater, it is found that (1) Matagorda Bay sediment contains trace elements in about the same concentrations as crustal rocks and shale but exhibits concentrations higher than seawater, and (2) only two elements, boron and mercury, identified within bay-system sediment exhibited anomalously high concentrations. These high concentrations are believed to result from man's activities within the Texas Coastal Zone.

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