Climate-induced changes in fluvial ichnofossil assemblages of the Pennsylvanian–Permian Appalachian Basin

The long-term response of riparian communities to shifting climatic conditions can be addressed by the ichnofossil record, because organism behavior is typically altered in response to changes in environmental factors. During the late Paleozoic, the Appalachian Basin experienced a shift from an ever-wet to wet–dry climate. Changes in the abundance, diversity, density, and composition of ichnofossil assemblages were investigated in fluvial point bar sandstones from five roadside outcrops of the Middle Pennsylvanian-to-early Permian Allegheny, Conemaugh, Monongahela, and Dunkard groups located in southeast Ohio and northwest West Virginia. Ichnofossil data were collected using a 0.5 × 0.5-m grid placed on bedding plane surfaces and from vertically oriented thin sections. Abundance, density, diversity, and burrow widths increased through the study interval. Behaviors changed from stationary- to mobile-deposit feeding, while community composition shifted toward more established, permanent generalists. These changes in ichnofossil assemblages suggest that the shift to a drier, more pronounced seasonal climate made short- to long-term occupation of the point bar sands more advantageous as surface conditions were more unfavorable and resources limited. This study helps us understand how terrestrial community composition and ecosystem dynamics shift over long time intervals in response to environmental perturbations. By assessing these changes, we can better predict what future impacts climatic shifts will have on continental ecosystems and terrestrial communities.