Genetic Sequence Stratigraphy of Upper Desmoinesian Oswego Limestone Along Northern Shelf Margin of Anadarko Basin, West-Central Oklahoma

Timothy P. Derstine

The Pennsylvania Oswego limestone (upper Desmoinesian) in the vicinity of the northern shelf break of the Anadarko basin contains stratigraphic sequences and associated depositional facies that were controlled by eustatic variations in a slowly subsiding basin. Core descriptions, detailed well-log correlations, and facies maps of Oswego limestone in Dewey and Custer Counties, Oklahoma, supplemented by seismic data along dip profile, define at least two principal stratigraphic sequences separated by regional unconformities. In this area, oil and gas have been produced from phylloid algal-bank deposits that formed at the shelf margin. The algal-bank deposits that contain vuggy and moldic porosity are bound northward by wackestones of shelf facies and southward by tightly ca cite-cemented packstones that formed on the seaward margin in relatively high-energy environments.

The detailed well-log correlations that consider genetic units illustrate the evolution of these carbonate and locally clastic deposits along Oswego shelf-ramp-basin profiles as a consequence of sea level oscillations. Repeated successions of upward-coarsening shelf wackestones, algal-bank deposits with fringing packstones and scattered terrigenous clastics, and basinal shales are a depositional system tract associated with sea level lowstand. This lowstand system is capped in one of the principal stratigraphic sequences by a thin shale that reflects an episode of rapid relative sea level rise and flooding of the Oswego carbonate shelf. Black shales deposited during this rapid flooding event form a problematic downlapping unit, because terrigenous sediment was evidently supplied from oth the Oklahoma-Kansas area to the north and the Wichita-Amarillo high to the south. Highstand carbonate facies system are not present in the shaly cyclic sequences indicating drowning or backstepping of carbonate sources.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.