Browsing by Subject "Radioactive waste disposal -- Texas"

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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.
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.
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.
Lithology, microstructures, fluid inclusions, and geochemistry of rock salt and of the cap-rock contact in Oakwood dome, East Texas : significance for nuclear waste storage
(University of Texas at Austin. Bureau of Economic Geology, 1982) Dix, Owen R.
Oakwood salt dome in Leon and Freestone Counties, Texas, has a core composed of a diapiric salt stock at a depth of 355 m. A vertical borehole in the center of the salt stock yielded 57.3 m of continuous rock-salt core overlain by 137 m of anhydrite-calcite cap rock. The lower 55.3 m of rock salt exhibits a strong, penetrative schistosity and parallel cleavage dipping at 30 to 40 and more than 60 variably dipping layers of disseminated anhydrite. Anhydrite constitutes 1.3 0.7 percent of the rock-salt core. The upper 2 m of rock salt is unfoliated, comprising a lower 1.4-m interval of medium-grained granoblastic rock salt and an upper 0.6-m interval of coarse-grained granoblastic rock salt. An abrupt, cavity-free contact separates rock salt from laminated cap rock consisting of granoblastic-polygonal anhydrite virtually devoid of halite or pore space. Microstructures and concentration gradients of fluid inclusions suggest that the unfoliated rock salt at the crest of the salt stock was once strongly foliated, but that this fabric was destroyed by solid-state recrystallization. Downward movement of brine from the rock-salt - cap-rock contact was apparently accompanied by two recrystallization fronts. Dissolution of halite at the contact released disseminated anhydrite that presumably accumulated as sand on the floor of the dissolution cavity. Renewed rise of the salt stock closed the cavity, and the anhydrite sand was accreted against the base of the cap rock. Much, if not all, of the lamination in the 80 m of anhydrite cap rock may result from cycles of dissolution, recrystallization, and upward movement in the salt stock, followed by accretion of base of the cap rock. These processes, which are strongly influenced by fluids, act both to breach waste repositories and to geologically isolate them. Despite repeated attrition and uplift of the salt stock, the geologic system has the ability to offset, at least partially, these negative processes by self-sealing and recovery.
Studies of the suitability of salt domes in east Texas basin for geologic isolation of nuclear wastes
(University of Texas at Austin. Bureau of Economic Geology, 1980) Kreitler, Charles W.
The suitability of salt domes in the east Texas basin (Tyler basin), Texas, for long-term isolation of nuclear wastes is being evaluated. The major issues concern hydrogeologic and tectonic stability of the domes and potential natural resources in the basin. These issues are being approached by integration of dome-specific and regional hydrogeologic, geologic, geomorphic, and remote-sensing investigations. Hydrogeologic studies are evaluating basinal hydrogeology and ground-water flow around the domes in order to determine the degree to which salt domes may be dissolving, their rates of solution, and the orientation of saline plumes in the fresh-water aquifers. Subsurface geologic studies are being conducted: 1) to determine the size and shape of specific salt domes, the geology of the strata immediately surrounding the domes, and the regional geology of the east Texas basin; 2) to understand the geologic history of dome growth and basin infilling; and 3) to evaluate potential natural resources. Geomorphic and surficial geology studies are determining whether there has been any dome growth or tectonic movement in the basin during the Quaternary. Remote-sensing studies are being conducted to determine: 1) if dome uplift has altered regional lineation patterns in Quaternary sediments: and 2) whether drainage density indicates Quaternaq structural movement. On the basis of the screening criteria of Brunton et al. (1978), Oakwood and Keechi domes have been chosen as possible candidate domes. Twenty-three domes have been eliminated because of insufficient size, too great a depth to salt, major hydrocarbon production, or previous use (such as liquid propane storage or salt mining or brining). Detailed geologic, hydrogeologic, and geomorphic investigations are now being conducted around Oakwood and Keechi salt domes.