EFFECTS OF THE LATE PALEOZOIC CLIMATE TRANSITION ON SOIL ECOSYSTEMS OF THE APPALACHIAN BASIN, (MONONGAHELA AND DUNKARD GROUPS): EVIDENCE FROM ICHNOFOSSILS

The Upper Pennsylvanian to Lower Permian Monongahela and Dunkard groups of Ohio and West Virginia contain abundant paleosols possessing varying suites of ichnofossils. Through comparison to modern analogs, these ichnofossils serve as indicators of soil moisture, soil organic content, water table level, precipitation, evapotranspiration, and landscape stability. As a result, ichnofossils of soil fauna are excellent indicators of fluctuations in biological activity in response to changes in environment and climate through time. The Late Paleozoic transition is a critical interval in Earth history in terms of tectonics, climate, and life. Analysis of ichnofossils in paleosols can be used to refine the details of the changing terrestrial landscapes of this time.

A study along a 50 km long, north-south transect of multiple 30-50 m high sections of the Monongahela and Dunkard groups through southeast Ohio and West Virginia resulted in the recognition of 12 pedotypes with distinct ichnocoenoses. Ichnofossils included rhizoliths, lined and unlined burrows, plant-feeding traces, and coprolites produced by various plants, larval and adult arthropods, and vertebrates. Soil-forming environments included palustrine, levee, proximal to distal floodplain, interfluve, backswamp, marsh, and fen settings. In general, ichnocoenoses were less diverse and comprised of shallow and simple ichnofossils in poorly drained Entisols and Inceptisols of the lower part of the studied sections. Ichnocoenoses became more diverse and comprised of deeper and more complex ichnofossils in well-drained Vertisols in the middle portion of the section. Near the top of the studied section, diversity and abundance of traces decreased again, but maintained their depth in calcareous Vertisols. The ichnocoenoses indicate an upward decrease in precipitation and an increase in seasonality. In addition to this trend through time, however, the nature of the ichnocoenoses varied within each interval recording short-term oscillations in soil properties and precipitation.

Terrestrial ichnocoenoses serve as an important archive of environmental data not otherwise preserved in the sedimentary record. Analysis of these suites of ichnofossils is critical to evaluating climatic conditions in deep time and their effects on soil ecosystems.