Geomorphic evidence of Permian salt disolution, Hockley and Cochran counties, Texas
Ateiga, Abdalla Ali
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Geological investigation in Cochran and Hockley counties, Texas, indicates that subsurface dissolution of Permian salt beds has occurred and is an ongoing process, creating the abnormally high solute loads and saline springs in Paleozoic (mainly Permian) outcrops east of the Southern High Plains. The cumulative thickness of salt lost to dissolution exceeds 500 feet in the northern part of Hockley County, and as much as 500 feet have been removed from parts of Cockran County. Evidence of removal of the salt (mainly halite) and collapse of overlying beds is revealed by cross sections and isopach maps constructed from oil well geophysical logs. Surface manifestation of subsurface dissolution of Permian salt beds and resulting subsidence of overlying beds is indicated by the Anton, Smyer, Whiteface, and Block X basins in Hockley County, but similar relationships were not found in Cochran County. Dissolution has occurred principally in the Salado Formation, with deeper dissolution in the underlying Seven Rivers and/or San Andres formations. Varying amounts of stratigraphic displacement over the dissolution areas indicates that subsidence has been intermittent throughout post-Permian time. Limited thin-section data and geophysical logs show a lack of secondary porosity in the Dewey Lake Formation, thus the section may have acted as a regional aquiclude preventing the downward percolation of water from overlying Mesozoic and Cenozoic aquifers. However, point-source dissolution areas, overlain by the Smyer, Whiteface, and Block X basins, which are not closely related to major tectonic elements in the area, suggest dissolution resulting from the localized, downward infiltration of the groundwater.