CLIMATE-INDUCED CHANGES IN FLUVIAL ICHNOFOSSIL ASSEMBLAGES OF THE PENNSYLVANIAN-PERMIAN APPALACHIAN BASIN

The long-term response of terrestrial communities to shifting climatic conditions can be addressed by the ichnofossil record. Notably, continental ichnofossils represent a climate-sensitive component of terrestrial communities. They can, therefore, help interpret shifts in ecosystems because organism behavior is typically altered in response to changes in environmental factors. The Late Paleozoic included a shift from an ever-wet to wet-dry climate in the Appalachian Basin, making it an ideal study area for this problem. Changes in the diversity, abundance, complexity, and composition of ichnofossil assemblages were investigated in fluvial sandstones representing point bar successions from five roadside outcrops of the mid-Pennsylvanian to Early Permian Allegheny, Conemaugh, Monongahela, and Dunkard groups located in southeast Ohio and northwest West Virginia. Ichnofossil data was collected using a 0.5 x 0.5 meter grid placed on 8-16 positions along bedding plane surfaces in each outcrop. Samples were collected within the grids to make 43 vertically oriented thin sections to better assess total substrate disturbance. Ichnofossil abundance was determined by counting the number of traces, density by evaluating the ichnofabric index, and diversity by counting the number of unique ichnogenera present. Composition was assessed by evaluating ichnofossil complexity, measuring burrow widths, and the number of different behavioral classifications based on morphology. Abundance, density, diversity, and burrow widths increased through the sections. Behaviors changed from stationary- to mobile-deposit feeding while community composition shifted towards more opportunistic, generalist organisms. These changes in ichnofossil assemblages suggest a shift to a drier, more pronounced seasonal climate where short- to long-term occupation of the substrate became 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 time 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.