RESPONSE OF SOILS AND SOIL ECOSYSTEMS TO THE PENNSYLVANIAN-PERMIAN CLIMATE TRANSITION IN THE UPPER FLUVIAL PLAIN OF THE DUNKARD BASIN, SOUTHEASTERN OHIO, USA

Small scale studies (<1 km) of paleosols and ichnofossils yield high resolution data that can be used to assess autogenic and allogenic processes through comparison of spatial and temporal trends in their properties and compositions. Direct exposure to the atmosphere during formation make paleosols vital to the reconstruction of past climate while ichnofossils provide evidence of soil biota not typically preserved as body fossils making them critical to paleoecological analyses. The aim of this study was to bridge the gap in the Pennsylvanian-Permian terrestrial record of the Appalachian Basin and further understanding of the response of soils and soil ecosystems to Late Paleozoic climate transition. Field and laboratory analyses were used to gather data from Upper Monongahela and Lower Dunkard group paleosols on Ohio Route 33, Meigs County, Ohio along a 1400 m succession of outcrops. Paleosols and ichnofossils were described in the field and samples were collected for thin section analysis and determination of clay mineralogy and bulk geochemistry. Clay mineralogy was used to qualitatively assess paleoclimate and bulk geochemistry was used to calculate weathering indices and mean annual precipitation. The data were compared to contemporaneous paleosols 30 km to the north and other Late Pennsylvanian-Early Permian paleosols from the North American midcontinent. Observations of the field site suggest an overall drying trend overprinted by complex hydrologic variation. Each outcrop displays three distinct paleosol zones. Starting from the bottom of the section, Zone 1 is the most laterally variable and contains Inceptisols and Vertisols, Zone 2 contains Vertisols overprinted by a laterally continuous Gleysol and Histosol, and Zone 3 contains noncalcareous to calcareous Vertisols. These data suggest a strong autogenic influence and a semi-arid to arid seasonal climate during the formation of Zone 1 paleosols. Zone 2 paleosols suggest an initial semi-arid to arid seasonal climate followed by a temporary shift to a more humid climate. Finally, Zone 3 paleosols suggest a return to a semi-arid to arid seasonal climate with evidence of increasing aridity up section. Lateral variation of the paleosols suggests channel migration was a major autogenic control, however, a strong allogenic climate signal is preserved.