HOT SHALES AND COALS: KEYS TO CLARIFYING "CHEROKEE" STRATIGRAPHY WITHIN A SEQUENCE STRATIGRAPHIC FRAMEWORK

The Skinner and Prue Sandstones (Middle Pennsylvanian, Desmoinesian) are important oil- and gas-producing reservoirs whose stratigraphic positions were traditionally established by reference to limestone marker beds. The Prue sandstone interval was defined as being between the Oswego/Breezy Hill and Verdigris limestones, which mark the top and base, respectively. The Skinner interval included all strata between the Verdigris limestone at the top and Pink limestone at the base. Reliance on these carbonate lithostratigraphic markers serves correlation well unless the carbonate is absent or so poorly developed that it fails to generate a distinctive wireline-log signature or discernable change in penetration rate.

The Skinner and Prue sandstone intervals represent 3rd or 4th order stratigraphic sequences. Each major depositional cycle consist of a (1) lowstand fluvial-deltaic channel or valley fill, (2) transgressive coal and dark (hot) shale, and (3) highstand limestone and superjacent deltaic shale. In each cycle, the transgressive coal and hot shale occur within a few vertical feet of each other and the younger highstand carbonate. In areas where water depth or sediment influx hindered carbonate development, the associated hot shales and/or coals offer alternative marker beds whose distributions often exceed that of the carbonate. Hot shales represent slow rates of deposition that resulted during maximal flooding and inundation of the continent. Some hot shales can be correlated on a regional scale. However, they are not recognized in areas with high rates of sedimentation such as along the southern margin of the Anadarko basin proximal to the Wichita-Amarillo uplift.

Hot shales and coals were used to construct a chronostratigraphic framework for the Prue and Skinner intervals in the Cherokee and Anadarko basins when carbonate markers were undetectable. This framework was used to clarify stratigraphy, interpret depositional settings, and assess the impact of subsidence rates on sediment dispersal.