Linking Paleobiological Patterns across Geographic Scales during the Late Paleozoic Ice Age: An Example from the Upper Mississippian Illinois and Appalachian Basins, USA

Recently, paleobiologists have aimed to link biotic patterns among geographic scales to better understand how local and regional processes drive long-term, ecological and evolutionary trends. In this study, we analyzed and compared regional patterns of taxonomic richness, turnover, and community structure during the onset of the late Paleozoic ice age (LPIA) – an interval associated with global biotic and environmental change. We collected richness and abundance data within a highly resolved sequence stratigraphic framework of Upper Mississippian depositional sequences, which record the start of the LPIA and that have been correlated over 300 km across the Illinois and Appalachian basins.

We observed a marked shift in the structure of biotic gradients across the onset the LPIA in the Illinois Basin. However, in contrast to global level studies we find that extinction played no role in altering the communities in this region. Instead, biotic gradients shifted as the morphology of the Illinois Basin changed from a flat, shallow carbonate ramp, to a more steeply dipping, deeper water ramp. A comparison with faunas from correlative sequences in the Appalachian Basin shows that the diversity, composition, and structure of biotic gradients did not vary geographically. We suggest that because the Illinois and Appalachian basins were connected during the study interval, that taxa were drawn from essentially the same species pool in each region. Despite this, taxonomic turnover was greater between glacio-eustatic sequences in the Appalachian Basin. We suggest that because subsidence was slower and the Appalachian Basin was shallower overall, that its ecosystems were more greatly affected by eustatic fluctuations. Our findings indicate that regional diversity patterns do not match global patterns across the onset of the LPIA and that regional factors, such as basin morphology or subsidence rates, governed the composition and structure of communities in the study area.