SEEING THE LATE PALEOZOIC ICE AGE AT A FINER SCALE: ECCENTRICITY SCALE CONODONT O AND SR ISOTOPIC TRENDS

Icehouses have been relatively rare in Earth History, with only two major periods of continental glaciation since the evolution of multicellular life and vascular plants. The late Paleozoic Ice Age (LPIA), which occurred between 325 to 260 Mya, shared many similarities with the current icehouse, but was likely more dynamic and possibly more acute. One aspect of the LPIA that remains poorly constrained is the timing and extent of continental glaciers in southern Gondwana. There is increasing evidence that Southern Hemisphere glaciation was characterized by numerous ice sheets rather than a single massive ice sheet and that glacial events may have progressed diachronously across southern Gondwana during the Pennsylvanian and early Permian. The extent of continental ice and its volume in turn would have strongly impacted ocean circulation and glacioeustasy, climate, terrestrial biomes, continental weathering and likely atmospheric pCO₂. Low-latitude sedimentary archives of glacioeustasy capture the global sum of changes in ice volume and are argued as the most robust record of ice volume changes during the LPIA. Here we present a U-Pb calibrated conodont-based oxygen isotopic (d¹⁸O) record from the Donets Basin that is resolved at the eccentricity time-scale and argued to record changes in seawater d¹⁸O during several glacial-interglacial transitions of the LPIA. The influence of seawater temperature of measured conodont d¹⁸O is evaluated using published and new clumped isotope (D₄₇) temperatures from paleotropical precipitates. The percentage of surface vs. thermocline dwellers in the Donets limestones varies systematically with inferred sea level at the 10⁵ and 10⁶ yr scale. We couple conodont taxonomic trends with d¹⁸O and Sr isotopic compositions from key intervals of inferred rapid sea level and climate change in order to evaluate potential climate-weathering linkages and their impact on ocean chemistry and structure. Comparison of the conodont-derived records to contemporaneous sea-level, tropical climate, and paleo-atmospheric CO₂ records reveals coincident changes that indicate repeated perturbation to the climate system during our penultimate icehouse.