USING VARIATIONS IN ICHNOFAUNA AND PEDOGENIC PROPERTIES OF MIDDLE TO LATE PENNSYLVANIAN FLOODPLAIN PALEOSOLS TO DETERMINE THE IMPACT OF CLIMATE CHANGE ON EARLY SOIL ECOSYSTEMS

A rapid turnover from lycoposid- to fern-dominated wetlands occurred during the Middle to Late Pennsylvanian in North America. The extinction is hypothesized as a result of a transition from an ever-wet to a seasonally arid climate. This also would have affected a developing soil ecosystem. In southeast Ohio, this ecosystem change occurs near the contact of the Allegheny and Conemaugh Groups. The purpose of this study is to document changes in soil properties and ecosystems through the description of lithologic, pedologic, ichnologic, and paleontologic characteristics of 30 paleosol profiles.

Allegheny Group paleosols include less than 1 m thick, poorly developed gleysols and histosols. Ichnofossils consist of only shallow rhizoliths. Conemaugh paleosol properties vary between the lower Glenshaw and upper Casselman formations. Glenshaw paleosols are 1-3 m thick vertic calcisols and vertisols. Ichnofossils include rhizoliths, lined burrows, and mottles that follow passively-filled tunnels and chambers. Casselman paleosols are 1-8 m thick argillisols, compound calcic vertisols, and cumulative vertisols. Ichnofossils include rhizoliths, scratch-marked burrows, shafts with terminal chambers, subvertical tunnels, large sinuous tunnels, and 5-10 cm wide chambers. Geochemical analyses indicate an upward increase in oxidation, calcification, and salinization with decreased leaching. Using the chemical index of alteration, mean annual precipitation values were calculated as 1350 mm for the Allegheny Group, 600-800 mm for the Glenshaw Formation, and 1100 mm for the Casselman Formation.

The paleosols indicate the development of a seasonal distribution of rainfall and fluctuating soil moisture levels from the Middle to Late Pennsylvanian. Increased lateral variability of Conemaugh Group paleosols suggests that many of their features were the result of local hydrologic and biologic conditions that differed across the basin. Most ichnofossils represent locomotion, feeding, and dwelling behaviors of soil arthropods. Larger structures were likely temporary to permanent dwellings of tetrapods. Increasing ichnodiversity was likely due to changes in local hydrology and nutrient availability in addition to surface climatic conditions that resulted in the development of stable, well-drained soils.