THE PERMIAN BASIN - INTRACRATONIC SUBSIDENCE IN WESTERN PANGEA TRIGGERED BY COMPRESSION

One distinctive feature of the West Texas branch of the Ancestral Rocky Mountains is it's burial by over 2.5 km of post-deformational Permian strata - the Permian Basin. Subsidence probably began during ARM deformation in Pennsylvanian time, as evidenced by very limited subaerial exposure and erosion related to uplifts in the central basin. Subsidence increased in rate by the early Permian and continued to the end of the Permian. Permian subsidence resulted in the maintenance of isolated deep-water marine basins until Ochoan (late Permian) time, when they were filled with evaporites and nonmarine sediments. The thrusted Marathon orogen probably participated in this subsidence, as little clastic material was shed from this orogenic belt into the basin (and none in the Permian; Permian deep-water clastics appear to have northerly sources).

The margins of the Permian Basin have been modified during the Mesozoic, but the pattern of post-Wolfcamp Permian isopachs suggests a bowl-shaped subsidence centered on the Central Basin "Platform" or axis of uplift.

The size and shape of the Permian basin are similar to other intracratonic basins (Illinois, Michigan, Williston). One method to form these basins is suggested to be downwarping due to densification of the lower crust or lithosphere. The central basin area hosts a Tonian layered mafic complex, which was subjected to compression and thrusting in Pennsylvanian time. Depression of a mafic crust or its subjacent lithosphere may have been the driving force for Permian subsidence.