The use of chemostratigraphy to refine ambiguous sequence stratigraphic correlations in marine mudrocks. An example from the Woodford Shale, Oklahoma, USA.

Application of sequence stratigraphy to fine-grained lithologies has previously been hindered by the difficulty of identifying distinct facies shifts within mudrocks. Three cores fromLincoln, Pottawatomie and Pontotoc Counties in Oklahoma and two outcrops at the Hunton Anticline Quarry inMurray County, OK record both proximal and distal regions of the Arkoma Basin. Handheld X-ray fluorescence data and gamma-ray profiles together with lithological descriptions can be used to develop sequence-stratigraphic interpretations. Stratigraphic successions that are challenging to correlate based on gamma-ray (GR) profiles alone can be correlated accurately by utilizing surfaces that are recognized within chemostratigraphic profiles. Within the Arkoma Basin, Oklahoma, the chemostratigraphic profile of the Woodford Shale is interpreted within a sequence-stratigraphic framework using the following general criteria. The Lowstand Systems Tract (LST) is defined by increasing concentrations of Ti, Zr, Al and K as well as high levels of Mo and V. The Transgressive Systems Tract (TST) is defined by declining concentrations of Ti and Zr, although Al and K may remain elevated;Mo and V also show general declines. The Highstand Systems Tract (HST) is defined by increasing concentrations of Ti, Zr, Al and K, but is distinguished from the LST by low levels of Mo and V. [ABSTRACT FROM AUTHOR]