Applying Regional Chemostratigraphic Variability to Refine Sequence Stratigraphic Frameworks within the Woodford Shale, Oklahoma
Bryan W. Turner, Jessica A. Tréanton, and Roger M. Slatt
The Woodford Shale provides an opportunity to test recent advances in handheld XRF (HHXRF) technology to develop sequence stratigraphic frameworks by comparing chemostratigraphic profiles directly to gamma ray logs and measured stratigraphic sections obtained from the same locations. Gamma ray profiles allow a direct integration of these newly ob-tained chemostratigraphic profiles into previously interpreted sequence stratigraphic frameworks. One field site and three cores of the Woodford Shale have been scanned using the HHXRF to develop a preliminary analysis of the regional variability of chemostratigraphic profiles for this formation.
Three cores from Caddo, Washington, and Pottawatomie Counties in Oklahoma and one outcrop at the Hunton Anticline Quarry (HAQ) in Murray County, OK represent both proximal and distal environments of the Woodford Shale. Clean surfaces at each area are scanned at one foot intervals using the HHXRF to determine the elemental profiles. At the same resolution, a gamma ray profile is scanned using a GR scintillometer or core spectral gamma ray. The lithologic description, gamma ray profile, and elemental profiles are then used to develop the sequence stratigraphic interpretation.
Correlations based on regional scale variations in chemostratigraphic proxies show an overall increase in sedimentation in proximal settings with a decrease in sedimentation in distal settings. Drops in continentally derived sedimentation are interpreted from dilution of the Zr and Ti signals, associated with clastic sedimentation, relative to the concentration of K and Al which are associated with clay mineral accumulation. All these elements are regarded as relatively immobile elements. In the distal setting the chemostratigraphic ratios between clastic and clay proxies show a dilution of Ti and Zr between 10-60% in the upper Woodford relative to the lower Woodford, while in the proximal setting these ratios are concentrated up to 12-15% in the upper Woodford relative to the lower. These changes are indicative of a landward shift in sedimentation.
AAPG Search and Discovery Article #90205 © AAPG Geoscience Technology Workshop, Permian and Midland Basin New Technologies, September 4-5, 2014, Houston, Texas