MARINE SNOWSTORM DURING THE PERMIAN – TRIASSIC MASS EXTINCTION

The Permian/Triassic mass extinction (PTME) is marked by a significant disruption of the global carbon cycle, as expressed by significant excursions in both the inorganic and organic carbon isotope record. Carbon cycle models have predicted large increases in bioproductivity to explain these trends, yet organic carbon rich rocks are not observed in most shelf sediments deposited at that time. Anomalous carbon rich sediments have been reported from rare abyssal plains sediments in Japan, however, and we report similar occurrence in obducted slices of ocean crust exposed in New Zealand. At the Waiheke section black shales deposited at the PTME had estimated original mean TOC levels of 4.6 wt. %, and with a maximum of 14.5 wt. %, extraordinarily high values for deep ocean sediments. Detailed study shows that these organic rick deposits are dominated by lamalginites comprised of unicellar solitary or colonial phytoplankton. Such deposits are typically formed by ‘marine snow’ formed during algal blooms driven by ocean fertilization. We modelled the impact of Fe loading from Siberian Trap eruptions to demonstrate the impact this could have had on marine bioproductivity and to explain these open-ocean organic rich deposits. We suggest that the eruption led to a marine snowstorm across the Panthalassa Ocean, causing a significant carbon drawdown event.