RAPID SILL INTRUSIONS INTO EVAPORITE RICH SEQUENCES IN THE TUNGUSKA BASIN, SIBERIA; A PERFECT STORM FOR THE END-PERMIAN ENVIRONMENTAL CRISIS

The emplacement of the Siberian Traps Large igneous province (LIP) through the Tunguska Basin is regarded as the key player in end-Permian environmental crisis. Recent geochronology stress that sills were emplaced at the same time as the mass extinction, suggesting a causal relationship. Still, the lack of data from sills and contact aureoles in the Tunguska Basin represents one of the main challenges in understanding the link between the LIP formation and the crisis. Here, we present field data, petrography and geochemistry, thermal modelling, and results from a borehole database with more than 700 wells in the Tunguska Basin, where 293 boreholes are studied in detail and presented. The boreholes cover large parts of the basin, from Norilsk in the north (N69) to Bratsk in the south (N55), with a bias towards petroleum-bearing regions. In total, 93.5% of the studied boreholes contain sill intrusions. The sill thicknesses vary considerably from kilometer-scale intrusive complexes to individual thin sills of a few tens of meters. Thick sills are emplaced within the vast Cambrian salt formations, with average sill thicknesses in the 115-130 meter range. Petrographic investigations of metamorphic sediments, and thermal modelling of sediment heating, demonstrate high temperature devolatilization. Degassing to the atmosphere took place via explosive pipe degassing and gas seepage. We show that depending on the specific location within the province and the emplacement depth, the potential for degassing of both greenhouse gases (CH4, CO2), aerosols (SO2), and ozone destructive gases (CH3Cl, CH3Br) was substantial and can explain the end-Permian mass extinction.