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

dc.contributorUniversity of Texas at Austin. Bureau of Economic Geology
dc.contributorJackson, M. P. A.,-95.9167,31.6167,31.5167
dc.creatorDix, Owen R.
dc.descriptionTo obtain a print version of this publication visit: and search for: RI0120. Project funded by U.S. Dept. of Energy under contract no. DE-AC97-80ET-46617 (formerly contract no. DE-AC97-79ET-46605)
dc.description.abstractOakwood 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.
dc.description.departmentUT Libraries
dc.description.departmentBureau of Economic Geology
dc.format.dimensionsiv, 59 p. : ill., map ; 28 cm.
dc.publisherUniversity of Texas at Austin. Bureau of Economic Geology
dc.relation.ispartofVirtual Landscapes of Texas
dc.relation.ispartofReport of Investigations
dc.relation.ispartofseriesReport of Investigations (University of Texas at Austin. Bureau of Economic Geology), no. 120
dc.subjectRadioactive waste disposal -- Texas
dc.subjectSalt domes -- Texas
dc.titleLithology, microstructures, fluid inclusions, and geochemistry of rock salt and of the cap-rock contact in Oakwood dome, East Texas : significance for nuclear waste storage

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