EARLY EFFECTS OF THE LATE PALEOZOIC CLIMATE TRANSITION ON SOILS AND SOIL ECOSYSTEMS OF THE APPALACHIAN BASIN (CONEMAUGH, MONONHAHELA, AND DUNKARD GROUPS)

The late Paleozoic climatic transition is well represented by the upper Pennsylvanian to lower Permian Conemaugh, Monongahela, and Dunkard groups of the western Appalachian Basin. These units contain abundant paleosols possessing suites of ichnofossils that serve as indicators of soil moisture, organic content, water table level, precipitation, and landscape stability which can be used to refine details of changes in landscapes through time. A study of these paleosols through southeast Ohio and southwest West Virginia resulted in the recognition of 24 pedotypes formed in palustrine, levee, proximal to distal floodplain, interfluve, backswamp, marsh, and fen settings with distinct ichnofossil assemblages produced by various plants, gastropods, and larval to adult soil arthropods.

An up section shift in pedotypes from Argillisols to Vertisols and Calcisols as well as an increase in pedotype diversity records a profound change in soil-forming processes and landscapes. Late Pennsylvanian landscapes were characterized by well-developed, clay-rich soils of woodland ecosystems. By the early Permian, soils experienced strongly seasonal climates and prolonged dry periods, producing well-developed shrink-swell features and carbonate horizons. Climatic conditions, especially mean annual precipitation, were prone to shifting, resulting in a heterogeneous landscape that changed significantly through time. A corresponding upward increase in ichnofossil diversity and changing ichnocoenoses suggests an increased dependence on the soil as a refuge from extreme surface conditions, such as rapidly changing moisture or temperature, or as a food resource as surface food resources became more sparsely distributed. Both uses were shown by the morphologies of various dwelling and deposit feeding burrows that appeared in the Monongahela and Dunkard groups.

Overall, growing instability of the climate during the Pennsylvanian-Permian transition led to a more diverse, heterogeneous landscape in the study area which promoted colonization of a diverse assemblage of soil organisms. The trend toward more seasonal conditions and reduced surface vegetation made burrowing activities, such as feeding, dwelling, and brooding, more advantageous as it offered additional protection and a source of stored nutrients.