The end of the Permian period is marked by global warming and the
biggest known mass extinction on Earth. The crisis is commonly
attributed to the formation of the Siberian Traps Large Igneous Province
although the causal mechanisms remain disputed. We show that heating of
Tunguska Basin sediments by the ascending magma played a key role in
triggering the crisis. Our conclusions are based on extensive field work
in Siberia in 2004 and 2006. Heating of organic-rich shale and petroleum
bearing evaporites around sill intrusions led to greenhouse gas and
halocarbon generation in sufficient volumes to cause global warming and
atmospheric ozone depletion. Basin scale gas production potential
estimates show that metamorphism of organic matter and petroleum could
have generated > 100,000 Gt CO(2). The gases were released to the
end-Permian atmosphere partly through spectacular pipe structures with
kilometre-sized craters. Dating of a sill intrusion by the U-Pb method
shows that the gas release occurred at 252.0 +/- 0.4 million years ago,
overlapping in time with the end-Permian global warming and mass
extinction. Heating experiments to 275 degrees C on petroleum-bearing
rock salt from Siberia suggests that methyl chloride and methyl bromide
were significant components of the erupted gases. The results indicate
that global warming and ozone depletion were the two main drivers for
the end-Permian environmental crisis. We demonstrate that the
composition of the heated sedimentary rocks below the flood basalts is
the most important factor in controlling whether a Large Igneous
Provinces causes an environmental crisis or not. We propose that a
similar mechanism could have been responsible for the Triassic-Jurassic
(similar to 200 Ma) global warming and mass extinction, based on the
presence of thick sill intrusions in the evaporite deposits of the
Amazon Basin in Brazil. (C) 2008 Elsevier B.V. All rights reserved.