Precision Correlation of Kansas Pennsylvanian Cyclothems Emphasizing Wire-line Logs and Conodonts in a Sequence Stratigraphic Framework

LAMBERT, LANCE L., and PHILIP H. HECKEL, University of Iowa, Iowa City, IA, W. LYNN WATNEY and GENE M. STEVENSON, Kansas Geological Survey, Lawrence, KS, and JAMES E. BARRICK and DARWIN R. BOARDMAN II, Texas Tech University, Lubbock, TX

The lithologic components and genetic interpretation of classic Pennsylvanian cyclothems have clear counterparts in sequence stratigraphy. Blocky mudstones (paleosols) and associated extensive subaerial exposure surfaces bound individual cyclothems and represent type-1 sequence boundaries. The "middle limestones" represent flooding units that may be thin or absent, depending on the relative rate of marine inundation. Most "core shales" correspond to condensed sections accumulated during maximum flooding and are persistent from the basin to the upper shelf. They are generally characterized by abundant and diverse pelagic and nektobenthic organisms (notably conodonts), and by a high content of organic matter, authigenic minerals (especially phosphates), and certain heavy metals (notably uranium). The latter results in a greatly elevated gamma-ray log response. The "upper limestones" and deltaic portions of "outside shales" form highstand units consisting of numerous lithofacies representing various aggradational and progradational deposits.

Dense well-control with occasional cores provides a means to apply sequence-stratigraphic analysis to thin cyclothemic strata, which are below the resolution of conventional seismic profiles. A lithostratigraphic framework can be established by correlating the "core shales" using their distinctive gamma-ray log signature. Rapid conodont evolution has resulted in a characteristic fauna for most of these "core shales," thus providing biostratigraphic confirmation of the lithostratigraphic correlations. The widespread nature of these maximum transgressive deposits extends the utility of the conodont indicators across dissimilar biofacies and lithofacies that would otherwise be difficult to correlate. Integration of wire-line log and conodont data by core and outcrop study could lay the g oundwork for biostratigraphic analysis of "core shale" cuttings obtained during drilling.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)