Vertical and Lateral Variability in Paleosols and Ichnofossils of the Late Pennsylvanian Monongahela Group, Southeast Ohio: Local Complexity and Regional Patterns

Paleosols formed in response to the climatic and environmental conditions of geologic past. They are, therefore, very useful in the interpretation of paleoclimate and paleoenvironment. They are also important sources of paleoecological data in the form of trace fossils. The Late Pennsylvanian Monongahela Group of southeast Ohio is characterized by thin units of siliciclastic and carbonate rocks interpreted as continental deposits in floodplain, fluvial channel, small lake, and marsh environments. Most of the fine-grained siliciclastic units contain evidence of past pedogenic modification. The purpose of this study is to document changes in Late Pennsylvanian soil properties and ecosystems in southeast Ohio through the description of lithologic, pedologic, ichnologic, and paleontologic characteristics of 10 laterally extensive paleosol profiles along five closely spaced outcrops of the Monongahela Group within Athens County.

The Monongahela Group paleosols consist of blocky red, gray, and green mudstones from 0.5 to 2.5 m thick, containing yellow and green mottles, iron nodules, layers of carbonate nodules, slickensides, rhizoliths, and burrows. The assemblage of pedogenic properties lead to the classification of these paleosols as protosols, calcisols, gleysols, and vertisols. The properties of the paleosols, however, vary vertically through the Monongahela section and laterally across the different outcrops. The lateral variations reflect the small-scale complexity of the paleoenvironment across the Pennsylvanian alluvial plain. As a broad pattern, the paleosols indicate that the region was characterized by a seasonal climate with alternating wet and dry periods. The high degree of lateral variability of Monongahela Group paleosols, however, suggests that many of the pedogenic features were the result of local hydrologic and biologic conditions that differed widely across the basin.