Sequence boundaries and chronostratigraphic gaps in the Llandovery of Ohio and Kentucky: The record of early Silurian paleoceanographic events in east-central North America

Abstract

New and published data are integrated herein to resolve the age and stratigraphic relationships for problematic strata of the Aeronian and Telychian (Llandovery; Silurian) in Ohio and Kentucky (USA). At least two major depositional sequences were traced along the eastern flank of the Cincinnati Arch; these are separated by a regionally angular unconformity with complex topography. Underlying units are progressively truncated to the northwest while overlying strata change facies, condense, and onlap in the same direction. The basal unit of the upper sequence is the Waco Member of the Alger Shale Formation in Kentucky and southern Ohio and the Dayton Formation in western Ohio. A persistent, positive carbonate carbon isotope (δ13Ccarb) excursion associated with the mid-Telychian Valgu Event is recognized in the upper subunit of the Waco Member; the absence of a comparable signal in the Dayton Formation corroborates interpretations that it is significantly younger. The correlations proposed here can be used to understand the nuanced depositional history and chronostratigraphic completeness of the lower Silurian in eastern North America. This framework can be used to characterize sea-level history and local conditions that prevailed during global paleoenvironmental events.