Mid-Continent Section

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Geometry and distribution of depositional cycles in the Mississippian limestone, north-central Oklahoma


The Mississippian limestone contains a hierarchy of depositional cycles recognized in core and on wireline log signatures. In north-central Oklahoma, depositional cycles generally clean- or shallow-upward to a higher-energy boundary bed, which is succeeded by clay-rich and dark-colored limestone that represents a stratigraphic surface associated with flooding and initiation of the next cycle. Using core-calibrated wireline logs, a series of cross-sections were constructed to differentiate the cyclic subunits within the Mississippian limestone interval. Fabric and texture of these cycles were established using core descriptions and thin section petrography, which resulted in the identification of reservoir and seal facies. Cores from wells across several counties in northern Oklahoma were correlated to log signatures to provide a regional framework. Prominent flooding surfaces in core are expressed on logs as increased gamma-ray values above the cleaner, less clayey beds. Subdividing the Mississippian limestone in core and extending the internal stratigraphy by cross section and mapping using wire line log data resulted in the recognition of characteristics of reservoirs and seals within specific intervals. Cycles in the Mississippian carbonate can be correlated at the county scale, exhibit thickening across faults associated with the Nemaha Uplift, and have prograding geometries.