Sulfidic anoxia in the oceans during the Late Ordovician mass extinctions – insights from molybdenum and uranium isotopic global redox proxies

The Late Ordovician Mass Extinction wiped out 85% of animal species in two phases (LOME1 and LOME2). kill mechanisms for the extinction are debated, but deteriorating climate expansion marine anoxia appear to have been important factors. Nevertheless, spatial extent intensity its temporal relationship with extinctions not well understood. Here, we review existing global paleoredox proxy data based on molybdenum (Mo) uranium (U) isotopes from four paleocontinents combined new Mo isotope Dob's Linn, Scotland. Individually, these sedimentary records demonstrate significant redox fluctuations, our coupled dynamic oceanic mass balance model evolution U cycles reveals that globally expansive ocean is best constrained by ? 238 carbonates Anticosti Island record during LOME2. In addition, consider periodic sulfidic developing well-ventilated parts shallow oceans (e.g. warmer periods greater solar insolation) produced temporarily high seawater 98 values LOME1 accordance trends observed records. this view, oxygen loss had a causal role both Ordovician. • A across pulses at Ordovician–Silurian Boundary Stratotype (Dob's Scotland). Comparison Scotland, South China, Canada Libya. Evidence second pulse. Indication shallow-water euxinia first