ABSTRACT

Major Silurian rock units that crop out in stone quarries in Ohio are, in ascending stratigraphic order, the Lockport Dolomite, Greenfield Dolomite, Tymochtee Dolomite, and Bass Islands Dolomite. The Lockport Dolomite is the major reef-bearing unit; it contains metazoan, stromatolite, and thrombolite reefs. The Greenfield, Tymochtee, and Bass Islands Dolomites are all peritidal carbonate units in the Findlay arch region. The Tymochtee Dolomite in the Ohio basin, was formed in a carbonate-evaporite tidal flat (sabkha).

Possibly the most controversial aspect of Silurian rock units in the Findlay arch region involves whether or not episodes of evaporative drawdown took place in the Michigan basin during the Silurian. Since all of the Silurian rock units in the Findlay arch region represent overall shallow water shelf sedimentation, these units should have been very susceptible to subaerial exposure as a result of even "minor" episodes of evaporative drawdown in the Michigan basin. Major evidence bearing on this problem includes a major regional subaerial unconformity between the Lockport Dolomite and the overlying Greenfield Dolomite, and the nature, abundance, and stratigraphic position of microbialites (stromatolites and thrombolites) in Silurian rocks in the Findlay arch region. Complicating understanding of Silurian rocks units in Ohio is the role of tectonics. It is proposed that recurrent block faulting during the Silurian along the Findlay arch and the Cincinnati arch affected the sedimentology and degree of subaerial exposure of various Silurian rock units in western Ohio.