Sedimentology and Paleoweathering Trends of Devonian/Mississippian Boundary Strata, Northeast/Central Pennsylvania: Implications for Glaciation in the Appalachian Basin

The Late Paleozoic Ice Age (LPIA, late Devonian–late Permian) serves as the best deep-time paleoclimate analog for the current Cenozoic icehouse (low atmospheric CO2, widespread glaciers and forests, last complete icehouse-to-greenhouse transition). The sedimentary record of LPIA glaciation on Gondwana is well-documented, but evidence for glaciation in Euramerica remains disputed. Diamictites, rhythmites, striated clasts, and dropstones in the Appalachian Basin have been attributed to alpine glaciation in the paleotropics. This study investigates the depositional processes and paleoweathering history of late Devonian/early Mississippian sediments in the Appalachian Basin, Pennsylvania to test for a glacial influence. The Catskill, the diamictite-bearing Spechty Kopf/Rockwell, and the Pocono Formations were sampled and described. Samples were analyzed for major elements using X-ray fluorescence (XRF) for use in paleoweathering indices. Sedimentology results indicate that diamictites are closely associated with mass transport processes (slumps/slides) and sediment gravity flows (debris flows and turbidites). Soft sediment folds, load and flame structures, evidence of tractive flows, and sheared beds are common. Paleoweathering indices indicate relatively high chemical weathering throughout the latest Devonian into the Mississippian, which would be unusual if glaciers covered the study area for a prolonged period. These results suggest the Spechty Kopf diamictites in our study area were likely deposited by subaqueous debris flows rather than direct glacial emplacement. However, indirect glacial influence cannot be ruled out by the results of this study and further work needs to be completed over a wider area to test the extent and timing of the hypothesized glaciation.