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. Importantly, 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 eight positions along two different bedding plane surfaces in each outcrop. Ichnofossil abundance was determined by counting the number of individual traces, density was assessed by evaluating the ichnofabric index, and diversity was assessed by counting the number of unique ichnogenera. Composition was assessed by evaluating ichnofossil complexity, measuring the burrow widths, and evaluating the number of different behavioral classifications based on morphology. Samples were collected within the grids to make vertically oriented thin sections in order to assess the amount of vertical penetration of the substrate. This data was used to test the hypothesis that ichnofossil diversity and abundance would increase from the Allegheny to Dunkard groups, composition of ichnofossils would reflect a change to communities composed of mostly opportunistic, generalist organisms, and these changes likely resulted from a trend toward more reduced primary productivity due to a shift to a drier, more seasonal climate. This study will help 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.