END-PERMIAN MASS EXTINCTION FROM MASSIVE BASALT-COAL INTERACTION

The Great Dying at the end of the Permian Period preferentially decimated ~95% of carbonate shell-bearing marine organisms. Ocean acidification is a likely mechanism, as a dissolution horizon exists in carbonate sections at the boundary. It is well known that the Siberian flood basalts are contemporaneous with this mass extinction, but flood basalts do not release enough CO2 and sulfur at a fast enough rate to produce ocean acidification. Furthermore, flood basalts alone do not produce tall enough eruption columns to deposit these volatiles and particulates high enough into the atmosphere to have a rapid global impact. Here we suggest a viable extinction mechanism involving flood basalts that overcomes these problems. A massive intrusion of 1000s of cubic kilometers of basalt intruded 10s of meter thick coal beds mobilizing a comparable volume of coal over a broad area. Mechanically the deformable rheology and low density of the coal bed confined the basaltic magma into sills. Once heated to a few 100°C, the coal became viscous and released volatiles through a process analogous to industrial coke production. The coal-magma-volatile mixture behaved as a volatile-rich explosive magma with a viscosity similar to andesite or dacite, but a much lower density. This mixture ascended at numerous locations spaced scaling to the depth of the bed and ignited when it mixed with the air, forming widespread pyroclastic vents. The additional thermal and kinetic energy provided by coal ignition produced buoyant eruption columns capable of transporting volatiles and particulates much higher into the atmosphere than a typical phreatic eruption. Initially, dust quickly cooled the climate especially in the Northern Hemisphere. The sudden CO2 and methane release then resulted in strong global warming. There was insufficient time to renew the mixed layer of the ocean, resulting in much stronger acidification than in the present ocean. Overall, changes that occur over less than the lifetimes of organisms are more likely to have catastrophic biological effects than slow changes. Therefore a sudden massive release of CO2 from coal burning over a few years is a more likely mass extinction mechanism than the gradual release of CO2 from metamorphism over 10000s of years in the Siberian basin.