A major sulphur isotope event at c.510 Ma:: a possible anoxia-extinction-volcanism connection during the Early-Middle Cambrian transition?

A new approach to constraining seawater delta S-34 and sulphate concentration using francolite-bound sulphate reveals an abrupt increase in delta S-34 to +50% around the Early-Middle Cambrian boundary. Such high delta S-34 values are best explained by increased rates of pyrite burial due to ocean anoxia coupled with an increased sensitivity of the ocean sulphate reservoir to perturbations due to low sulphate concentrations of 500-700 mu gL(-1). We argue that the spread of anoxic waters at this time was partly the result of greenhouse warming related to the eruption of the Kalkarindji Large Igneous Province of northern Australia and that it triggered the collapse of early metazoan reef ecosystems during the latest Early Cambrian. Mass extinctions of the last 260 Myr have all coincided with enhanced volcanic activity, while several are also associated with positive shifts in seawater delta S-34. Extending this correlation back in time further implicates volcanically induced climate change as a major determining factor in biosphere evolution.