The Use of Chemostratigraphy to Refine Ambiguous Sequence Stratigraphic Correlations in Marine Shales: An Example from the Woodford Shale, Oklahoma
Bryan W. Turner, Jessica A. Tréanton, Roger M. Slatt, "The Use of Chemostratigraphy to Refine Ambiguous Sequence Stratigraphic Correlations in Marine Shales: An Example from the Woodford Shale, Oklahoma", Sequence Stratigraphy: The Future Defined, Bruce Hart, Norman C. Rosen, Dorene West, Anthony D’Agostino, Carlo Messina, Michael Hoffman, Richard Wild
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Identifying distinct facies shifts within mudrocks has made it difficult to build sequence stratigraphic frameworks within fine-grained lithologies. Three cores from Lincoln, Pottawatomie, and Pontotoc counties and two outcrops at the Hunton anticline quarry in Murray County cover proximal and distal regions of the Arkoma basin within southern Oklahoma. Chemostratigraphic and gamma-ray profiles supplemented with lithologic descriptions can be used to build sequence stratigraphic interpretations within mudrock systems.
Detrital sediment input is associated with Ti, Zr, Al, and K. The degree of basin restriction correlates with Mo and V concentrations, barring certain mineralogical affinities. Silicon is found in biogenic quartz, detrital quartz, feldspars, and clays. However, evaluating Si as a ratio between Si/Al, in conjunction with the Ti and Zr concentrations, the Si/Al ratio provides a rough approximation for the amount of biogenic quartz present within a sample. At several horizons in the Woodford, the Si/Al value spikes, and the Ti and Zr values drop; these spikes are interpreted as planktonic blooms.
Stratigraphic successions with ambiguous gamma-ray profiles correlations can be correlated accurately by utilizing surfaces that are recognized within chemostratigraphic profiles. Within the Arkoma basin, the chemostratigraphic profile of the Woodford Shale is interpreted within a sequence-stratigraphic framework using the following general criteria. Progradational packages record increasing concentrations of Ti, Zr, Al, and K. Retrogradational packages record a declining trend in these elements, indicating the transgressive systems tract. Lowstand system tracts and highstand system tracts can be distinguished by the degree of bottom-water restriction. Low base level correlates to a greater degree of basin restriction.