Marine Anoxia as a Potential Trigger for Mid-Carboniferous Biocrisis

The mid-Carboniferous Serpukhovian biocrisis ranks as the second-order mass extinction of the Phanerozoic. Although climatic cooling has been attributed as the chief driver, the kill mechanisms for this mass extinction remain uncertain, in part owing to its synchroneity with a widely developed unconformity linked to Gondwanan glaciation and the Hercynian Orogeny. Here, we present high temporal-resolution, coupled carbon and uranium isotope records from a mid-Carboniferous (332–320 Ma) carbonate slope succession in South China spanning this event. Our records shed light on the evolution of global carbon-cycle dynamics and ocean-redox conditions during the Serpukhovian biocrisis. While the long-term cooling and Gondwanan glaciation could have caused thermal stress on the paleotropical ecosystem and resulted in a large glacio-eustatic fall and thus reduction in shelf niches, expanded area in marine anoxic seafloor, particularly on limited shelf regions, would also have exerted additional environmental stress.