THE END-PERMIAN ENVIRONMENTAL CRISIS TRIGGERED BY VOLCANISM AND SEDIMENT DEGASSING OF THE TUNGUSKA BASIN, SIBERIA

The emplacement of the Siberian Traps Large Igneous Province is regarded as the main trigger of the end-Permian environmental crisis. The causal link is, however, still under investigation. We propose that the main trigger of the environmental crisis was the eruption of large volumes of poisonous gases from the intensely intruded Tunguska Basin in Siberia. Over the past decade we have collected extensive field and borehole samples from both the intrusive complexes and the sedimentary host rocks from Bratsk in the south to Norilsk in the north. The samples have been analyzed and dated by petrographic, organic and inorganic geochemical, biostratigraphical, and high-precision zircon TIMS geochronological methods. The sill geometries and thicknesses vary considerably from kilometer-scale intrusive complexes to local meter thick sills. Thick sills (up to 900 meters in thickness) occur in high abundance in the upper part of the sedimentary succession, affecting the coal-rich Tunguska Series sediments and deeper Cambrian salt formations and organic-rich rocks. Petrographic investigations of the metamorphic sediments demonstrate that widespread high temperature devolatilization took place. We show that depending on the specific location within the province and the emplacement depth, the potential for degassing of greenhouse gases (CH4, CO2), aerosols (SO2), and ozone destructive gases (CH3Cl, CH3Br) was substantial and can explain the crisis. The geochronological data further reveal a strong temporal correlation between the magmatism and the environmental crisis, supporting the aureole degassing hypothesis.