Cincinnatian Geology in Southwest Hamilton County, Ohio

Abstract

Cincinnatian rock units in southwest Ohio are distinguished here for mapping purposes on the basis of their bulk lithologic characteristics: specifically, the proportion and relative thickness of interbedded limestone and shale. Clastic-ratio and bedding-index logs derived from detailed section measurements confirm the observed lithostratigraphic relations. The predominance of either shale or limestone strata in alternating sequence results in a succession of rock units with distinctive lithofacies that grade into or intertongue with each other. Earlier Cincinnatian nomenclature is largely biostratigraphic by definition and commonly inapplicable in practical field and subsurface studies. The lowest strata are referred to the Kope Formation. A distinctive sequence of strat in the upper Kope is proposed as a member. Fairview is redefined as a lithostratigraphic unit. Kope-Fairview relations require recognition of a lower Fairview and an upper Kope tongue. A unit of recurring Kope lithofacies overlies the Fairview. Bellevue is redefined as a rock unit. Direction of regional dip corresponds with direction of intertonguing. Dominantly calcareous units are structurally high. They grade laterally into shaly units that are correspondingly low. Regional dip is partly lithofacies controlled. A simplified grouping of seven existing and three newly proposed limestone classes expresses the gradational differences in their sedimentary history and depositional environments. Distribution of the groups illustrates that the bulk of limestone deposition occurred in a high-energy environment, probably governed by the existence of shallow shoal banks.