Analysis of the cyclostratigraphy at the Devonian-Carboniferous boundary in south-central Oklahoma

Abstract

An outcrop in La Serre, France, was officially ratified by the ICS in 1989, and the IUGS in 1990, as the location of the Global Boundary Stratotype Section and Point (GSSP) for the Famennian–Tournaisian, and subsequently the Devonian–Carboniferous (D–C) boundary. GSSPs, like this one, are official outcrops that provide physical representations of geologic time boundaries, essentially geological standards that define geologic time, providing a vital framework to model a variety of interpretations of geological phenomena from paleoclimate to paleontological. It has been acknowledged that the GSSP in La Serre, France is in need of revision due to fossil reworking and general outcrop quality. The D–C boundary has also traditionally been a challenging boundary to place with precision because of problems associated with Siphonodella sulcata, whose first occurrence is the current definition of the boundary. With the aim of improving D–C boundary correlation, especially in the central United States, outcrops from the Woodford Shale in south-central Oklahoma and a New Albany Shale core from Johnson County, Indiana have been analyzed for cyclostratigraphy through measurement of mass-dependant, low-field magnetic susceptibility (χ), and also gamma radiation (GR). Gamma Ray Spectroscopy (GRS; field based) measurements were used for general correlation, along with previous conodont biostratigraphic work. Combined use of χ and GR measurements for 40K allows for a deeper layer of stratigraphic comparison. With the combined statistical techniques of the periodogram, multi-taper method (MTM), and wavelet analysis, a detailed timescale was pieced together for both the Oklahoma outcrops and Indiana core by comparing the periodic elements of the cyclostratigraphic signal represented by these geophysical proxies. Future work studying faunal assemblages can be compared with the cyclostratigraphic framework provided here to allow greater precision in interpretation.