PERMIAN BASIN

also called West Texas Basin, large sedimentary basin in western Texas and southeastern New Mexico that is noted for its rich petroleum and natural-gas deposits. It originated as a marine basin bordered by extensive deltas during the Permian and Triassic periods (between 286 and 208 million years ago). The Permian Basin consists of three connected but distinct areas of subsidence, which are, from east to west, the Midland Basin, Central Basin, and Delaware Basin. These smaller basins are separated from one another by platforms, areas of relatively thin sedimentary strata. Great subsidence during the Permian Period, coupled with limited access to the ocean, resulted in the deposition of salts (from which evaporite minerals later precipitated) in the basins and the formation of large barrier reefs that abounded with diverse marine fauna around them. The occurrence of large quantities of oil and natural gas in the Permian Basin is attributable to subsurface remnants of Permian reefs; these reefs were rich in plant and animal remains that developed into petroleum and collected in the porous formations. Numerous oil fields also occur in the geologic remnants of the lagoonal deposits that formed behind the reefs.