Devonian upper ocean redox trends across Laurussia: Testing potential influences of marine carbonate lithology on bulk rock I/Ca signals

The Devonian is characterized by major changes in ocean-atmosphere O 2 concentrations, colonialization of continents plants and animals, widespread marine anoxic events associated with rapid δ 13 C excursions biotic crises. However, the long-term upper ocean redox trend for still not well understood. This study presents new I/Ca data from well-dated Lower through Upper limestone sections Great Basin (western Laurussia) Illinois (central Laurussia). In addition, to better address potential influences lithology stratigraphy on signals, are reported here as carbonate lithology-specific. Results indicate that lithologic do exert a dominant control bulk trends, but effects some diagenetic overprints cannot be ruled out. For Basin, low values (more reducing) recorded during Pragian Emsian increased fluctuating Eifelian Givetian. trends suggest local oceans were more reducing Lochkovian, oxic Pragian-Emsian, return Eifelian, then increasingly oxic, Givetian-Frasnian. variations at likely share similarity global condition (compared Basin) based its position adjacent Panthalassic Ocean temporal co-variation environmental volatility trends. overall variable conditions (if signal) Middle Late coincide evidence suggesting seawater may have been an important part instability this time.