DEATH METAL IN THE EARLY PALEOZOIC

Some, if not most, of the major Ordovician-Silurian extinction events coincided with glacial episodes. However, it has become increasingly clear that cooling, itself, is not a viable kill-mechanism to explain these extinctions. Interestingly, these events are announced by the appearance of malformed organic-walled fossil zoo- and phytoplankton. New geochemical analyses (using ToF-SIMS and LA-ICP-MS) of these teratological microfossils and their host rocks, through a mid-Pridoli event, show a correlation between teratology and a dramatic increase in redox sensitive metals. By analogy with metal-induced teratology in modern marine environments, our results suggest that these in vivo teratological reactions result from the pollution of the Silurian marine environment by toxic metals. These new data appear to link the initiation of the mass extinctions with the cycling of harmful redox sensitive metals likely related to Ocean Anoxic Events (OAEs), rather than with climate change. Our work introduces metal-induced teratology as a potential and independent proxy for the monitoring of paleo-ocean geochemistry in deep time.