Quaternary Stratigraphy of the Western Rolling Plains of Texas Preliminary Findings

Quaternary deposits, as much as 76 m (250 ft) thick, discontinuously cover more than 7,800 km2 (3,000 mi2) of the western Rolling Plains of northwestern Texas. The stratigraphy of this sedimentary sequence is complex, reflecting changes in paleoclimate during the late Pleistocene and Holocene Epochs. In addition, there are clear indications of syngenetic structural control of deposition and postdepositional deformation of the Quaternary strata. These effects were caused by regional and local karstic subsidence resulting from dissolution of Upper Permian evaporites, particularly halite, at depths of 120 to 240 m (400 to 800 ft). Dissolution created voids within the bedded evaporites. As the voids expanded, the overlying strata collapsed, forming depressions wherein sediment accumulated preferentially. Subsidence also caused local faulting and downwarping of some of the Quaternary deposits. Affected deposits include beds of coarse-grained sediment eroded from the westward-retreating Caprock Escarpment (adjacent to the Rolling Plains). This sediment was trapped within the zone of subsidence, forming a broad bajada at the base of the escarpment. At most sites, the coarse-elastic deposits compose the lowest of three genetic components of the regional Quaternary section.