INTEGRATIVE CARBON ISOTOPE ANALYSIS OF THE LATE ORDOVICIAN, EDENIAN STAGE, KOPE FORMATION STRATOTYPE

The Late Ordovician, Kope Formation has a well-established sequence- and chemo-stratigraphic framework which has been extensively researched. A large roadcut along KY-445 in Brent, Kentucky provides an almost complete exposure of the Late Ordovician, Kope Formation, which has been used as the new stratotype of the Edenian Stage and a key reference section for research on biostratigraphy, faunal gradient analysis, and magnetic susceptibility data and cyclostrigraphy/astrochronology. However, no carbon isotope data, a key chronostratigraphic tool, previously existed for this section. The Kope Formation contains a variety of facies including shale, siltstone, and fossiliferous limestone but most are calcareous enough for δ¹³C_carb analysis. This project focused on the generation of whole rock carbon isotope data and correlation with regional chemostratigraphic frameworks.

Carbon isotope analysis of the Brent, Kentucky section allows previous correlations made on the basis of faunal horizons, event beds, and biostratigraphy to be tested with a new tool. The carbon isotope profile of the KY-445 outcrop is atypical of units of a similar age, as it is fairly uniform in appearance. Most of the absolute values are between 0 ‰ and -1 ‰ with an average variation of ~0.5 ‰. One exception is a significantly negative excursion reaching -4.4 ‰ at its minimum, at 13 meters from the base of the outcrop. This negative excursion occurs below the lowest occurrence of Geniculograptus pygmaeus at this locality. The Kope excursion is expected to show a ~1 ‰ increase from background values, but the results of the 445-KY data set show lower variability of only ~.5 ‰. This integration of high resolution isotopic, biostratigraphic, and magnetic susceptibility data allows for detailed characterization and correlation from this classic reference locality.