Lower Permian (Wolfcampian) Shelf-Margin Reefs and Associated Carbonate Facies of the Subsurface Central Basin Platform and Hueco Mountains Outcrop Analogs, Permian Basin, West Texas, USA
Lower Permian (Wolfcampian) carbonate shelf-margin stratigraphic architecture and reef development in the Permian Basin were controlled by regional tectonic pulses and associated erosion during the earliest and middle Wolfcampian, and by glacioeustatic sealevel trends. On the Central Basin Platform, Lower Hueco (early Wolfcampian) shelf-margin bank complexes with reefs grew along the face of a Bursum (latest Pennsylvanian) erosional escarpment. Basinward of the escarpment margin, the Lower Hueco bank is >200 ft thick, but on top of the platform the Lower Hueco is only about 50 ft thick. The Lower Hueco shelf-margin bank growth position was controlled by tectonic uplft and erosion at an earliest Wolfcampian unconformity, and by relatively low early Wolfcampian sealevel highstands. The shelf-margin bank has >100 ft thick reef-mounds flanked by packstones-grainstones. Reef bafflestones-boundstones have a framework of phylloid algae, calcisponges, and erect bryozoans, which are encrusted by Tubiphytes, Archaeolithoporella laminar algae, and sparse fistulioporid bryozoans. Syndepositional peloidal cement and radial fibrous cement are common. Crestal shelf-margin shoals prograded over the reefs and are composed of coarse grainstones with fusulinids, Tubiphytes, and dasycladacean algae. Back-shoal facies are finer peloidal-skeletal packstones-grainstones that grade shelfward into phylloid algal-fusulinid wackestones and packstones. Lower Hueco shelf-margin reservoir porosity was created by dissolution at the mid-Wolfcamp unconformity. Upper Hueco (late Wolfcampian) carbonates backstepped over the Lower Hueco bank, and have thickness and facies patterns controlled by mid-Wolfcampian structural movements and erosional topography.
Hueco Mts. Wolfcampian shelf-margin outcrop analogs have phylloid algal reef-mounds that grade upward into grainstone shoals with Tubiphytes patch reefs and shelfward into skeletal-peloidal packstones-grainstones. Proximal forereef facies are crinoidal limestones and forereef tongues of lithoclastic-skeletal packstones. Distal slope-to-basin facies are dark cherty mudstones-wackestones with interbedded lithoclastic-skeletal debris flows and turbidites. Lower Hueco shelf-margin complexes prograded southwestward, and the Upper Hueco backstepped, similar to the eastern Diablo Platform and the Central Basin Platform.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California