Large perturbations of the carbon and sulfur cycle associated with the Late Ordovician mass extinction in South China

High-resolution δ¹³C data of organic carbon from a continuous section of the Late Ordovician–Early Silurian reveal two positive δ¹³C excursions that are associated with the mass extinction in South China. The first stratigraphic δ³⁴S measurements on pyrite tied to well-established biostratigraphy indicate a large perturbation of the sulfur cycle, consistent with major sea-level changes related to the glaciation. The elevated δ³⁴S values of pyrites and a large, short-lived negative δ³⁴S excursion of ~20‰ associated with the decay of the glaciation suggest deep-water anoxia during the Hirnantian Stage, in contrast to the conventional view that the global oceans were oxygenated. We suggest that deep-water anoxia may have contributed to the Late Ordovician mass extinction in South China and possibly elsewhere.