The Delaware basin of west Texas and southeast New Mexico is the most negative structural unit of the southern Permian basin. It occupies an upper Paleozoic intermontane trough between the Central Basin Platform Mountains and the Ancestral Rockies. Before the development of these ranges, this area formed part of the broad Tabosa sag which accumulated shelf deposits from Lower Ordovician through Mississippian. These sediments consisted largely of carbonates and shallow water shales. The Delaware basin, as a structural and stratigraphic unit, began developing in Early Pennsylvanian. Extensive subsidence coupled with compressive faulting converted the axial portion of the Tabosa sag into the Central Basin Platform Mountains and raised the Diablo arch to the west. An east dip ing half graben, the Delaware basin, developed between these uplifts. Water depths in the southern and eastern portions of this basin probably exceeded 2,000 feet throughout the Pennsylvanian. The deep areas are characterized by starved shale sections. Pennsylvanian shelf limestones cover the shallows along the north and northwest margins. Permian tectonism deepened the basin and elevated the marginal mountains. Fault displacements

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along the western edge of the Central Basin platform exceeded 12,000 feet. Shelf limestones were deposited on the marginal shallows, but turbidites and flysch poured in to practically fill the basin during the Wolfcampian. Subsidence continued during the Leonardian, which is characterized by bedded sands, dark limestones and dark shales. In the Guadalupian, the reef-bordered marginal limestone shelves began encroaching on the semi-starved sand and shale floored basinal area. This forestepping was checked when reef growths sealed off the seaward opening to the basin. Upper Permian, Ochoan, evaporites furnished the final filling for the structurally negative Delaware basin. Overlying Triassic terrestrials and Cretaceous shelf limestones show no evidence of a buried deep basin in the are .

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