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Abstract
The Ordovician–Silurian contact in parts of the Cincinnati Arch region is an irregularly pitted erosion surface reflecting karstic weathering during a lower-mid Silurian (Aeronian) lowstand, superimposed on the Hirnantian–Rhuddanian Cherokee Unconformity. This irregular unconformity is overlain by a unit termed the “golden Brassfield”, which grades laterally into strata identified as the “red Brassfield”, a probable equivalent of the Oldham Limestone to the east–southeast. These units are Aeronian or early Telychian, considerably younger than the Rhuddanian–early Aeronian Brassfield Formation sensu stricto. Preservation of erosional topography, resulting from rapid flooding and burial of karstic surfaces, is typical of unconformities representing moderate durations.
Acknowledgements
Funding for this research was provided by NSF Grant EAR 0819820 to CEB, a Dry Dredgers Paul Sanders Award to JRT, and Society for Sedimentary Geology (SEPM) and Geological Society of America (GSA) student research grants awarded to NBS. Patrick Cullen and Daniel List (University of Cincinnati) provided field assistance. Kyle Hartshorne (Dry Dredgers) assisted significantly with research into Brassfield stratigraphy. Previous versions of this article were improved by reviews by Bradley D. Cramer (University of Iowa) and Markes E. Johnson (Williams College). This is a contribution to the International Geoscience Programme (IGCP) Project No. 591 – The Early to Middle Paleozoic Revolution.