ABSTRACT

Previously, Upper Pennsylvanian carbonate rocks and associated strata in southeastern Ohio were interpreted as freshwater deposits. Detailed examination of these units has led to the recognition of depositional environments which include marine, intertidal, and supratidal.

Upper Conemaugh units contain an abundant marine fauna and grade upward into lower Monongahela sandstone, shale, and coal. Monongahela sandstones occur as elongate, lenticular bodies. Thin sandstone beds which extend from the lenticular sandstone and interfinger with green shale contain rip-up limestone fragments, stromatolites, and mudcracks. Middle Monongahela limestones and dolomitic limestones overlie these sandstones and shales and are interbedded with green shale. The carbonate rocks contain a sparse fauna of ostracods, gastropods, pelecypods and, locally, fish teeth and scales. Carbonate rocks are thick-bedded, brecciated micrites which contain bird’s-eye structures, gypsum crystal molds, and stromatolites. Red-mottled claystones dominate the upper part of the sequence and are interbedded with thin, nodular, conglomeratic algal limestones.

Upper Conemaugh strata represent shallow-marine deposition offshore from a shifting Monongahela barrier-bar system. Behind these barrier bars, coal swamps developed which evolved into tidal flats on which dolomitic carbonate muds and clay muds were deposited. As tidal flats became more extensive, supratidal conditions developed, ranging from hypersaline to fresh water and subaerial, and clay and carbonate muds were deposited.

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