Relation Between Sedimentation and Diapirism at the Davis Hill Salt Dome, Liberty Co., Texas

A. Muzaffar¹, J. R. Kyle¹, and B. Vendeville^2
1Department of Geological Sciences
²Bureau of Economic Geology, The University of Texas at Austin, Austin, TX

The Davis Hill dome is a relatively large salt stock with an area of more than 5 square miles, situated 60 miles northeast of Houston. The minimum depth is about 800 ft to the cap rock and about 1,200 ft to salt. The source layer (Jurassic Louann Salt) lies at a depth of at least 30,000 ft. Seismic and well log interpretation suggests that diapir growth took place from late Cretaceous to Plio-Pleistocene. Passive growth (Downbuilding) of the dome stopped during Vicksburg deposition followed by active growth (Upbuilding) of the dome. Present day topographic relief at Davis Hill is 175 ft above the surrounding coastal plain. A radial pattern of oxbow lakes above the dome suggests that the dome is still rising, but the present day topographic maximum does not correspond to the apex of the dome.

Studies of two complete cap-rock cores indicate that the cap rock comprises anhydrite, gypsum and calcite zones from bottom to top that total about 440 ft thick. The anhydrite zone represents the more resistant components of the salt that accumulated as the halite was dissolved by pore fluids. The calcite zone formed by bacterial alteration of sulfate accompanying hydrocarbon destruction. The calcite zone in these cores contains significant amounts of sulfide minerals and oil. The sulfide-rich calcite zone is approximately 40-ft thick and is dominated by locally massive iron sulfides. Zn-Pb sulfide occurrences are scattered throughout the core. Minor realgar (AsS) occurs in the cap rock, a mineral unknown elsewhere in the Gulf Coast.

AAPG Search and Discovery Article #90901©2001 GCAGS, Annual Meeting, Shreveport, Louisiana