Minor Δ33S anomalies coincide with biotic turnover events during the Great Ordovician Biodiversification Event (GOBE) in South China

In this study, we report multiple S-isotopic data (δ34S and Δ33S) of sedimentary pyrite in Early to Late Ordovician sections from South China. The results reveal two distinct groups of negative Δ33S anomalies during the Dapingian and Sandbian to Early Katian stages, which coincide with two faunal turnover events. The negative Δ33S values reflect the mixing of sulfides with strongly negative δ34S and positive Δ33S, and sulfide with strongly positive δ34S and positive Δ33S. This mixing scenario may have resulted from the impinging of deep anoxic waters onto the continental shelves possibly facilitated by sea-level rise. The temporal co-occurrence of negative Δ33S anomalies with intervals of faunal turnover in brachiopod assemblages of South China suggests that the encroachment of anoxic waters may have driven the diversity crises. Our results provide evidence for a dynamic mechanism linking the recurrent upwelling of deep anoxic waters and faunal turnovers during the Early to Late Ordovician