CONSTRAINING REDUCING CONDITIONS IN THE PRAGUE BASIN DURING THE LATE SILURIAN LAU/KOZLOWSKII EXTINCTION EVENT

The Silurian was marked by repeated extinctions, carbon cycle volatility, and significant intervals of climatic change. The most notable of these events were the Ludfordian Lau/Kozlowskii extinction and associated Mid-Ludfordian Lau carbon isotope excursion, both of which have been linked to a period of global cooling and expanded reducing conditions in the global oceans. Here we present new data that characterize marine paleoredox conditions of the Prague Basin, a peri-Gondwanan terrane. This study utilizes iodine-to-calcium ratios to assess local redox conditions in a shallow water carbonate succession and iron speciation and redox-sensitive trace element concentrations to assess local redox conditions of a deeper water sequence. Consistently low values of I/Ca in the shallow water section suggest either persistent local anoxia or possibly diagenetic overprinting. Iron speciation data suggest that bottom water redox conditions in the deeper shelf setting were consistently anoxic with possible intermittent euxinia. Concentrations of redox-sensitive trace elements consistently higher than upper continental crust values also indicate persistent reducing conditions in the deeper part of the basin. These local redox proxy data, taken in concert with trends in new pyrite sulfur isotope (δ³⁴S_pyr) data, are consistent with findings that major changes in global marine redox conditions occurred during this interval of the late Silurian.