ANALYSIS OF LANDSCAPE VARIABILITY THROUGH THE PENNSYLVANIAN-PERMIAN MONONGAHELA AND DUNKARD GROUPS, SOUTHEASTERN OHIO, USA

Paleosols and ichnofossils of the Late Pennsylvanian to Early Permian Monongahela and Dunkard groups of southeast Ohio provide significant paleoenvironmental data related to the Late Paleozoic climatic transition. The purpose of this study was to better understand how increased drying and seasonality of this time affected terrestrial paleolandscapes on a local scale and climatic variability on a regional scale. Twenty-six paleosols from three outcrops in between Athens and Coolville, Ohio were investigated. Methods included the description of paleosol profiles in the field and the analysis of thin sections. Clay mineralogy and bulk geochemistry were used to assess weathering processes and paleoprecipitation. Initial results, such as the distribution, abundance, and size of physical features including slickensides, pedogenic carbonates, and rhizoliths, as well as a transition from gleyed and weakly developed paleosols at the base to oxidized, well-developed, vertic paleosols at the top of the section record responses of the paleosols to alternating mildly seasonal to strongly seasonal conditions with a shift from more seasonally wet to seasonally dry conditions through the study interval. Paleosols of the Monongahela Group are interpreted as mildly to strongly seasonal, wet to wet-dry, sparsely to heavily vegetated fens to woodlands, forming on proximal to distal floodplain environments. Paleosols of the Lower Dunkard Group are interpreted as a strongly seasonal, wet-dry, sparsely to moderately vegetated scrublands to woodlands, forming on proximal to distal floodplain environments. Two adjacent outcrops with coeval paleosols allowed the assessment of lateral variability resulting from autogenic processes. Little lateral variation occurred in the lower portion of these sections, but variation increased up section suggesting a greater influence by autogenic processes. The overall vertical pattern of environmental change, however, remained the same. Variability in climate has occurred throughout geologic time having profound effects on paleolandscapes. By investigating changes in paleosols through episodes of climatic transition, we can better understand the impact these changes have on soils and soil ecosystems of the past and future.