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The Detection and Importance of Subtle Biofacies within a Single Lithofacies: The Upper Ordovician Kope Formation of the Cincinnati, Ohio Region

¹ Department of Geology, University of Georgia, Athens, GA 30602-2501
² Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013
³ Department of Geosciences, Weber State University, Ogden, UT 84408

Environmental controls on the distribution of fossils most commonly are found by recognizing that certain distinctive fossil assemblages are associated with particular lithofacies. Lack of change in lithofacies commonly is used as indicating a lack of significant environmental effects on the stratigraphic distribution of fossils. The results presented here challenge that view. The Upper Ordovician Kope Formation of the Cincinnati, Ohio, area has long been considered a single unit, both lithostratigraphically and in terms of depositional environment. Gradient analysis of over 1000 fossil assemblages reveals subtle environmental control on the distribution of fossils, in the absence of obvious lithologic change. This gradient analysis is used to construct an ecological model of the Kope fauna, with values of preferred depth, depth tolerance, and peak abundance estimated for the most common fossils. This method, conducted within a single lithofacies, offers the potential for reconstructing sequence architecture because faunas can be more sensitive recorders of environment than lithofacies. In addition, the presence of subtle facies control as in the Kope raises the prospect that environmental controls on paleobiologic and biostratigraphic patterns may be more pervasive than generally acknowledged.