Permian Cyclic Strata, Northern Midland and Delaware Basins, West Texas and Southeastern New Mexico

Abstract

Permian cyclic rocks of Wolfcampian-Guadalupian age in the northern Permian Basin, West Texas and southeast New Mexico, are grouped into five regionally extensive lithofacies: (1) shelf evaporite-carbonate, (2) shelf detritus, (3) shelf-margin carbonate, (4) basin carbonate, and (5) basin detritus. Recognition of these lithofacies within an unconformity-bounded sequence suggests the following sedimentary model. During normal sea-level conditions, Wolfcampian-Guadalupian shelf-margin reefs and banks formed near sea level. The resultant backreef lagoon was shallow but very broad; therefore little terrigenous sand reached the distant basin. Deposition of shelf-margin carbonate was at a maximum and the sediments accumulating in the basin were chiefly pelagic mud and micrite. Relative lowering of sea level, possibly eustatic-epeirogenic, initiated regression, causing continental and nearshore sand and mud to prograde across the lagoon. Continued progradation enabled shelf detritus to enter the basin through numerous reentrants and submarine canyons dissecting the shelf margin; additi nal regression subaerially exposed the shelf clastic beds, providing an unconformity-delimited datum surface. Flooding of the shelf by transgression restricted the supply of detritus and reactivated normal carbonate deposition. Correlation of a shelf-detritus top with a coeval basin-detritus top provides the framework for Wolfcampian-Guadalupian shelf-to-basin correlations.