155 Stratigraphy (Posters) I

HIGH RESOLUTION CORRELATION OF THE SHAWNEE GROUP (VIRGILIAN, PENNSYLVANIAN) IN KANSAS AND OKLAHOMA

Paper number: 155-8
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

This study utilizes lithocorrelation, correlation of surface generated spectral gamma-ray scinillometer, and conodont biostratigraphy in order to correlate Shawnee Group Strata from Kansas into Oklahoma. The Shawnee Group (Pennsylvanian, Virgilian) extends from Iowa, Nebraska, Missouri, and Kansas into northern Oklahoma. The cyclothemic succession is remarkably consistent from Iowa to Kansas with an abrupt lithofacies change occurring at the Kansas-Oklahoma border. This change in lithofacies succession represents shelfal deltaic deposition in the Oklahoma region. This results in some members such as the Heebner Shale thickening from 2-3 meters to 20 meters with interbedded sandstones because of high stand-deltaic progradation. These deltaic wedges greatly complicate correlation of individual members and formations from Kansas into Oklahoma. It is largely for this reason that the stratigraphic terminology utilized in Oklahoma differs substantially from that utilized in Kansas and northward. Additionally, Osage County, that is the county adjacent to Kansas, has not had a completed geologic map created, further complicating correlation.

Marine condensed sections within the Shawnee Group including the Heebner Shale, Queen Hill Shale, and Larsh-Burroak Shale have been physically traced using field mapping, gamma-ray analysis and conodont biostratigraphy. These condensed sections can now be used for surface-to-subsurface correlations of individual cyclothemic sequences utilizing gamma-ray signatures and biostratigraphic ties. Limestone units that are extremely widespread and continuous north of Oklahoma are found to be lenticular and are only traceable locally for short distances in Oklahoma. A number of local names used for these limestones in Oklahoma can now be dropped and their Kansas equivalents can be adopted.