PALEOENVIRONMENTAL INFERENCES BASED ON FOSSILS AND LITHOLOGY OF AN OUTCROP OF THE UPPER PENNYSLVANIAN AMES MEMBER OF THE GLENSHAW FORMATION (CONEMAUGH GROUP), SOUTHEASTERN OHIO

The Upper Pennsylvanian Ames Member of the Glenshaw Formation outcrops in several counties in southeastern Ohio. This study concentrated on an outcrop in Noble County near Dudley, Ohio that consists of at least 4 ft (1.1 m) of basal dark gray, fossiliferous shale overlain by 1 ft (0.3 m) of light to medium gray, fossiliferous limestone . The evidence presented by several recent studies suggests that the Ames Member represents a relatively rapid transgressive-regressive cyclothemic sequence deposited by the Midcontinent Sea across this area in response to glacial-eustatic sea level changes. The Ames Member represents the marine transgression-regression unit overlying the Harlem Coal (not exposed at this locality) and at this location appears to represent a single transgression followed by a regression. Faunal analysis of the dark gray shale indicates that the shale represents a marine offshore lithofacies containing fossils indicative of an environment that had dysaerobic bottom conditions. This biofacies is dominated by the opportunistic thin-shelled brachiopod Neochonetes sp., but also contains small benthic molluscs. The limestone is dominated by crinoid columnals and pieces of stems, but also contains the brachiopods Neochonetes sp., Neospirifer cameratus, Juresania sp., and Linoproductus sp.; the bryozoans Rhombopora sp. and fenestellids; a few complete gastropods and bivalves and fragments of bivalves and gastropods; and shark teeth. This biofacies is dominated by stenohaline epifaunal suspension feeders and is interpreted to represent open marine, low turbidity, clear water conditions. The upper few inches of the limestone is a biocalcarenite consisiting of fragmented mollusc shells, brachiopod shells, and crinoid columnals with a lesser abundance of whole fossils, and may represent more shallow water conditions with stronger current action. This may (in part) represent the regressive portion of the sequence, however, with low detrital input and turbidity due to the distance from the Appalachian Highlands source area to the southeast and position on the cratonic ramp near the outer (western) edge of the Appalachian Basin. Nonmarine mudstone overlies the limestone lithofacies.