Revised Conodont Biostratigraphy for Lower Silurian Surface and Subsurface Strata of the Cincinnati Platform and Appalachian Basin and Implications for Ohio’s Lower Silurian “Layer-Cake” Stratigraphy

Kleffner, Mark A.
Department of Geological Sciences, The Ohio State University at Lima, Lima, OH

The upper part of the Brassfield and the “Stray Clinton” are within the D. kentuckyensis Zone in Adams, Brown, Greene, Miami, and Preble Counties (Cincinnati Platform) and Ashtabula, Licking, Mahoning, Muskingum, and Perry Counties (Appalachian Basin). Neither formation is younger than middle Aeronian. The Dayton in Adams and Brown Counties is within the Pt. eopennatus Zone (early Telychian). The “Packer Shell” in Ashtabula and Mahoning Counties is within that zone and also the succeeding Pt. am. angulatus Zone (early Telychian). The Dayton in Greene and Miami Counties and the “Packer Shell” in Licking, Muskingum, and Perry Counties are within the Pt. am. amorphognathoides Zone (late Telychian). The Dayton in Preble County is within the Pt. am. amorphognathoides through O. s. rhenana Zones (early Sheinwoodian). The Brassfield/Dayton contact in Adams and Brown Counties and “Stray Clinton”/”Packer Shell” contact in Ashtabula and Mahoning Counties are both unconformities representing the middle Aeronian to early Telychian. The Brassfield/Dayton contact in Greene, Miami, and Preble Counties and the “Stray Clinton”/”Packer Shell” contact in Licking, Muskingum, and Perry Counties are also unconformities representing the middle Aeronian to late Telychian.

The Dayton and “Packer Shell” are significantly diachronous. All Silurian time scales published since 1989 show a duration of at least 1.5 my for the Telychian. It seems unlikely that transgression of the epeiric sea over the exposed and eroded Brassfield and “Stray Clinton” of Ohio during the late Llandovery required 1.0 my or more. Instead, both the Dayton and “Packer Shell” are more likely names given to several different units that all have the same basic stratigraphic position, suprajacent to the Brassfield or “Stray Clinton.”

AAPG Search and Discovery Article #90031©2004 AAPG Eastern Section Meeting, Columbus, Ohio, October 3-5, 2004