REEVALUATION OF THE SUNBURY SHALE (MISSISSIPPIAN) AND RELATED STRATA OF THE APPALACHIAN BASIN IN OHIO

The brownish-black, carbonaceous Sunbury Shale represents an upper transgressive phase of the widespread Devonian-Mississippian black shale sequence of the North American mid-continent region. Surface exposures in the southern and central Ohio portions of the Appalachian basin show the Sunbury overlies the Berea sandstone and siltstone, a regressive deltaic sequence, and is overlain by various regressive siliciclastic lithologies of the Cuyahoga Formation. Identification and correlation of the Sunbury, based on limited exposures, suggest the shale has a maximum thickness of slightly more than 40 feet near its type section in central Ohio but thins southward and merges with the underlying Devonian Ohio Shale near Irvine, Kentucky, to form the upper portion of the New Albany Shale. In northern Ohio, the Sunbury is reported to consist of brownish-black to bluish-black shale that is about 25 feet thick near Berea but thins to the east and pinches out near the Ohio-Pennsylvania line. The Sunbury is the basal part of the Orangeville Shale Member of the Cuyahoga Formation in northern Ohio. The Sunbury is not exposed between central and northern Ohio outcrop areas because of glacial cover; thus, correlation between these regions has been based on meager well data and drillers’ reports. Recent mapping and a reevaluation of the relationship between the Sunbury and the overlying Cuyahoga indicate the Sunbury consists of a wedge of brownish-black shale that thickens to over 110 feet in north-central Ohio. Eastward, the Sunbury grades laterally into Cuyahoga rocks that formed as prograding delta and shelf sediments contemporaneous with Sunbury deposition. The Sunbury Shale in southern and central Ohio is coeval with the Orangeville Shale Member, Sharpsville Sandstone Member and, in part, the Meadville Shale Member of the Cuyahoga Formation of northeast Ohio and western Pennsylvania.