LINKING MIDDLE TO LATE PENNSYLVANIAN CLIMATE CHANGE TO VARIATIONS IN ICHNOFAUNA AND PEDOGENIC DEVELOPMENT IN FLOODPLAIN AND LACUSTRINE PALEOENVIRONMENTS OF THE APPALACHIAN BASIN

The transition from an ever-wet to a seasonally arid climate during the Middle to Late Pennsylvanian (Desmoinesian - Missourian) impacted a complex and diverse terrestrial ecosystem. A rapid turnover from lycoposid- to fern-dominated wetland forests occurred at the time of this climate shift in North America. In southeast Ohio, this transition occurs near the contact of the Allegheny and Conemaugh Groups. The purpose of this study is to determine the effects of the climate change on paleosol properties and soil ecosystems represented by ichnofossils. Field studies involved the description lithologic, pedologic, ichnologic, and paleontologic changes in paleosol profiles below, within, and above the Desmoinesian–Missourian boundary. Ichnofossil distribution was used to define a vertical sequence of changes in soil biota diversity, abundance, and tiering with respect to pedogenic development and paleoclimate.

Allegheny Group paleosols are tan to gray-green, contain platy and blocky ped structures, preserved organic matter and plant fossils, rhizoliths, and thick horizons of clay concentration characteristic of argillisols. These paleosols are typically capped by a thick coal unit indicating the presence of a high water table and mire development. Conemaugh Group paleosols are red-green to red-yellow, contain angular blocky ped structures, horizons of calcium carbonate nodules, rhizocretions, little organic matter, abundant ichnofossils, and pseudoanticlines associated with slickensides characteristic of vertisols. Changes in paleosol properties indicate the transition from an ever-wet climate with poorly drained soils in the Desmoinesian to a seasonally dry climate, well-drained soils in the Missourian. Additional overprinting of different pedogenic properties within individual paleosol profiles both below and above the contact is diagnostic of variable climatic and hydrologic conditions during paleosol development. These features suggest short-term local or regional changes during the development of a single paleosol profile. Ichnofossil assemblages also vary across the Desmoinesian–Missourian boundary. The diversity, abundance, and distribution of ichnofossils prove to be excellent indicators of soil moisture, water table level, precipitation, and environmental stability.