PRELIMINARY REVISION OF THE SEQUENCE STRATIGRAPHY AND NOMENCLATURE OF THE UPPER MAYSVILLIAN-LOWER RICHMONDIAN STRATA EXPOSED IN KENTUCKY

Late Ordovician (Katian) strata of Kentucky, in the Cincinnati Arch region, display a regional change in lithologic and faunal gradients corresponding to a southeast-shallowing epicontinental ramp. While a detailed sequence stratigraphic framework has been established for the lower Cincinnatian, that of the upper Maysvillian-lower Richmondian succession of northern and central Kentucky has not been studied in detail. Moreover, locally and inconsistently applied lithostratigraphic terms reflecting facies changes along the ramp have complicated precise subdivisions of sequences into component cycles and inhibited recognition of regionally consistent patterns.

This study uses high-resolution facies analysis and tracing of distinctive stratigraphic markers including biostromal horizons, rhythmic intervals, erosion and flooding surfaces, and distinctive fossil epiboles across lithofacies and nomenclatorial boundaries to reveal stratigraphic consistencies largely overlooked by previous researchers. By using these methods, it is possible to refine the depositional sequences whilst creating a nomenclature that can be applied more consistently throughout the region. Preliminary results indicate that much of the past terminology can be retained and refined, allowing the use of one unified set of names on the member scale level that will be integrated into formations. This will allow easier correlations along the Cincinnati arch. Moreover, this will lead to a refined sequence stratigraphic framework for a better understating of depositional environments and changes in faunal gradients. Because these sequences span offshore to peritidal facies they provide the possibility of testing for changes in sequences and their component systems tracts across a proximal-distal gradient. Finally, the beds record the onset of the Richmondian invasion and high-resolution stratigraphy will provide a framework to examine the details of this important ecological evolutionary event.