Abstract: Subsurface Siluro-Devonian Carbonate Interval (Bass Islands-Columbus/Onondaga and Oriskany in Ohio

Alan H. Coogan

Siluro-Devonian dolomite and limestone strata in the subsurface of Ohio consist of zero to 650 feet of late Bass Islands dolomite, Devonian Helderberg (Keyser) limestones, Oriskany sandstone (of Ohio), and the Columbus and Delaware (Onondaga) limestones. The sequence is ripped up by unconformities causing the Silurian Salina and Bass Islands dolomites to toplap below the Columbus Limestone on the "Bass Islands platform". The gas-producing Oriskany sandstone is limited to the "Helderberg basin" northeast of the Cambridge Arch. In that basin, Oriskany strata are absent over the Silurian Niagaran reef. In contrast, the Columbus Limestone thickens over the Niagaran reef. In the northeastern portion of the "Helderberg basin", Oriskany and Helderberg strata are preserved like t e Salina B salt; i.e. they occur north of a line marked by the Smith-Suffield-Akron fault zone. Southwest of the Cambridge Arch, the Silurian Bass Islands Dolomite is beveled by erosion, then onlapped by the Columbus Limestone. At the wedge edge just north of the Rome Trough in Kentucky, all Salina strata are removed by subaerial erosion and then onlapped by the Devonian shale. From the wedge edge, the Devonian limestone depocenter is northeast, a departure from the southeast direction of the depocenter of earlier Silurian deposition.

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas