Abstract
Pennsylvanian cyclothems record climatic variability during the late Paleozoic Ice Age, Earth's penultimate glaciation. Cyclothems form from fluctuations in global sea level caused by the waxing and waning of continental ice, or glacio-eustacy. Magnitudes of glacio-eustatic change are typically inferred from facies stacking patterns and stratal geometries but can also be determined by oxygen isotopic shifts archived in fossils within cyclothems. Fossil oxygen isotopic composition records seawater oxygen isotopic composition, which is a function of both global changes in ice volume and local hydrologic processes. Here we utilize conodont chemistry to quantify changes in global ice volume and local hydrology of the Midcontinent Sea, USA. Conodont oxygen isotope and strontium isotope time series within the lower Kasimovian (Pennsylvanian) Swope Cyclothem of Kansas City, MO exhibit episodic variability. Decreases in oxygen isotopic composition accompanied by increases in strontium isotopic composition indicate episodic influxes of fresh water to the Midcontinent Sea. Increases in the carbon to nitrogen ratio and carbon isotopic composition of associated organic matter confirm these findings. Collectively, these geochemical measurements inform an inverse model used to quantify the freshwater influx driven by increased tropical precipitation. Conodont and rock geochemical time series enable isolation of the freshwater influx signal on glacio-eustatic estimates derived from intra-cyclothem changes in conodont oxygen isotopic composition. Conodont geochemistry reveals and quantifies both global and local climatic variability during deposition of a Pennsylvanian cyclothem.