November Monthly Luncheon

Greenhouse conditions of the early Paleozoic contributed to increased ocean stratification and the development of widespread deep-water anoxia. An expanding geochemical dataset from marine sedimentary rocks from the Argentine Precordillera suggests changing nutrient availability under fluctuating climatic conditions during the Middle Ordovician. Changes in ocean circulation patterns resulting from global cooling in the Middle-Late Ordovician would have led to the disruption of stratified ocean waters characteristic of early Paleozoic greenhouse environmental conditions, upwelling of nutrient-rich deep water, and perturbations in oceanic nutrient budgets. Evidence for such oceanographic change is found worldwide in the C- and S-isotope records of marine carbonate in the Middle Ordovician as the Middle Darriwilian isotope carbon excursion (MDICE) and large changes to the marine sulfur cycle recorded in carbonate associated sulfate (CAS) and pyrite (PY).