PALEOENVIRONMENTAL RECONSTRUCTION OF A FOSSIL-RICH PENNSYLVANIAN-PERMIAN OUTCROP, DUNKARD GROUP, SOUTHEASTERN OHIO, USA

An outcrop on the eastern side of the north fork of Veto Lake in southeastern Ohio preserves a rich record of flora and fauna associated with the Pennsylvanian-Permian transition. The purpose of this study was to examine the sedimentology and paleontology of the outcrop in order to reconstruct the paleoenvironment, and to assign an age to the rocks. The outcrop consists of interbedded sandstones and mudstones. Sandstones are fine to very fine grained, decimeters to ~2 m thick, and exhibit trough cross stratification, current ripple cross lamination, 3-D combined-flow ripple marks and cross laminae, planar stratification, and trace fossils. Paleoflow was to the NNW. Sandstones tend to thin laterally and one splits laterally as it thins. Individual mudstones are decimeters to ~1.5 m thick. One type of mudstone is dominated by planar laminae, but displays cross laminae locally. In places, some of these mudstones exhibit mudcracks. Other mudstones display turbation, ped structures, slickensides, clay cutans, small calcite nodules, and iron oxide segregations indicative of pedogenesis. Well-preserved plant fossils are abundant as impressions within mudstones. Tree trunks also are preserved locally. Plant fossils are dominated by the tree fern Pecopteris (52% of the 1436 plant fossils identified) with fewer Sphenophyllum, Lepidodendron, Neuropteris, and other plants. Faunal remains and traces include ostracods, spiral worm tubes, xenacanth shark coprolites, and the trace fossils Skolithos, Cruziana, Scoyenia, & Cochlichnus. Faunal and floral evidence suggest brackish to fresh water conditions. Collectively, the data indicate that the depositional environment was an interdistributary bay or lake (possibly both at different times) that was occasionally subject to changes in water levels. Laminated mudstones represent deposition within the bay/lake in slow moving or stagnant water. Sandstones are interpreted as crevasse splay and/or levee deposits that episodically prograded into the bay/lake. Alternations between subaqueous laminated mudstones and subaerial paleosols & mudstones with mudcracks reflect episodic changes in water levels. The fossils present are common to both the Upper Pennsylvanian and Lower Permian, and suggest that the strata are part of the Pennsylvanian-Permian transition zone.