LANDSCAPE AND CLIMATE RECORDS DERIVED FROM DEVONIAN VERTIC FLOODPLAIN PALEOSOLS, CATSKILL FORMATION, CENTRAL PA

Changes in paleosol morphology and chemistry resulting from pedogenesis within differing paleoenvironments were evaluated for Devonian Catskill Fm. exposures near Selinsgrove, PA. Systematic changes that occur upward in the stratigraphic section include: 1) increasing size, depth and density of root traces, 2) increasing abundance and thicknesses of pedogenic carbonate horizons, and 3) increasing morphological and chemical development of paleosols. Irish Valley (IV) paleosols formed in muddy coastal-margin environments characterized by repeated small-scale transgressive-regressive cycles and generally contain both vertical and horizontal, small (1-3 mm diameter, 5-15 cm long), clay-lined root traces. Many IV paleosols show significant retention of primary depositional fabrics, either due to low density of plant cover or to transgressive events that terminated pedogenesis. Pedogenic carbonate horizons in IV paleosols are very sparse, thin, and consist of dolomitic lenses with tubular-fenestral morphology, suggesting precipitation in association with mat-like vegetation of diminutive stature. Sherman Creek (SC) paleosols, in contrast, formed in a lower to middle alluvial plain setting, characterized by sluggish, low-gradient rivers and by poorly to moderately drained floodplains subjected to rare marine incursions associated with incised valley fills. Pedogenesis was more complete, evidenced by greater thicknesses of profiles and their differentiation into distinct "horizons", especially pedogenic carbonate (Bk) horizons, probably due to a more significant plant cover and more time for pedogenesis between floodplain depositional events. Root trace size increases upward through the SC, from small near the base, to large stature, drab-haloed root traces (up to 5 cm diameter, up to 0.5-1 m long) within the middle and upper SC member, which indicate existence of arborescent vegetation, perhaps large lycophytes or progymnosperms. Pedogenic carbonate horizons in SC paleosols are morphologically complex, dominated by rhizolith morphology, and partial replacement of micrite and calcite by dolomite is common. These observations suggest strong control of paleoenvironment, especially soil drainage and salinity, as well as geomorphic stability, on early and mid-Paleozoic soil systems.