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Cambrian-Ordovician of North-Central Ohio

James A. Noel

Recent exploration activity in Richland and Ashland Counties, together with an interest in the correlation problems related to the Trenton-Black River and Black River-Gull River boundaries, prompted this subsurface study. The study area in north-central Ohio includes eastern Morrow, western Knox, Richland, northwestern Ashland, western Medina and Loraine, and eastern Huron Counties.

An examination of geophysical logs and completion records at the Ohio Geological Survey reveals that there are nearly as many opinions about the locations of the Trenton-Black River and Black River-Gull River boundaries as there are geologists who correlate them. Additionally, it has been suggested that all of the production in Morrow and adjoining counties is not Trempealeau but may be Gull River or even Black River. This study presents evidence to solve the correlation problems and therefore the source of the production.

Outside of Morrow County, in the study area, 338 wells have been drilled into Cambrian sediments. Of these, 11 were drilled to the Precambrian. Two wells are currently being drilled in Richland County. Of the 338 wells, 63 have been producers. The wells were drilled in clusters surrounding early producers, so that regional analysis requires some interpretation.

Cross sections, structure contour maps, and isopach maps substantiate the conclusions concerning the correlations and present a valid portrayal of the Cambrian-Ordovician stratigraphy.

AAPG Search and Discovery Article #91031©1988 AAPG Eastern Section, Charleston, West Virginia, 13-16 September 1988.