Department of Earth Sciences
Fall 2022 Seminar Series
Dr. Amy Weislogel
Friday September 23, 2022
12:30PM
Storrs Hall WW16
Dynamics of rivers and forests during glacial-interglacial climate cyclicity: Lessons from the Late Paleozoic Ice Age Abstract:
Climate models over century time scales forecast anthropogenic greenhouse gas emissions will cause significant loss of polar ice, a climatic phenomenon last experienced during closure of the Late Paleozoic Ice Age (LPIA). Deep-time LPIA records are needed in order to better forecast magnitudes, rates, drivers and impacts of this change on terrestrial systems and critical zones (i.e., TS/CZ) that are vital to human civilization. Furthermore, TS/CZ dynamics hold important implications for feedback processes that compound climate variation (e.g., peat burial, alluvial chemical weathering, pedogenic carbon deposition). Among the richest archives of low-latitude TS/CZ deposits is the Allegheny foreland basin in West Virginia, which formed far from the shoreline, preserving hydrologic depositional signals unaffected by glacioeustacy. We conducted detailed sedimentologic analysis of the Middle Pennsylvanian Allegheny Formation, and determined that lower sandstones were deposited by shallow, multi-thread channels with high flow velocities. This suggests low-latitude TS/CZ environments experienced aridity and extreme seasonality during a period when coeval atmospheric composition models indicate overall low, fluctuating pCO2 (200-600 ppm) conditions. However, younger Allegheny Formation sandstones display attributes indicating deposition by deeper, single-thread channel morphologies, consistent with a meandering fluvial system. This fluvial style shift could reflect a climatic shift toward wetter conditions, consistent with the increased lycopsid abundances observed in the associated Lower Kittanning coal, or alternately could reflect increased water delivery due to tectonic-driven change in fluvial catchment hydrology. The latter hypothesis is supported by sandstone petrology data that reflects a decrease in lithic grain abundance with overall increasing detrital feldspar abundance in these younger channels. We hypothesize that this sandstone composition signals orogen unroofing during waning uplift of the Blue Ridge Thrust Complex, likely accompanied by drainage catchment expansion that facilitated a more sustained water discharge to the basin year-round. Ongoing work will generate improved chronostratigraphic, paleotemperature and provenance models to more precisely align fluvial sedimentation and intervening paleosol/coal deposits to pCO2 conditions developed over 10^5 cycles, providing multiple, natural glacial-interglacial climate cycles to compare with the ongoing anthropogenic-influenced climate phase.
For more information, contact: Christin Donnelly at christin.donnelly@uconn.edu