Tunguska сoals, Siberian sills and the Permian-Triassic extinction

Abstract

The latest Permian-Triassic volcanism that created the Siberian traps, including the products of the explosion and interaction of the magmas with regional volcanic and sedimentary rocks, is now considered to be the main driving forces of the end-Permian mass extinction - the greatest global extinction in the Earth history. As proposed, the trap magmatism induced metamorphism of the sedimentary succession that released the sediment-derived CO2 from the thermogenic cracking of coal by intrusive heating. Although the coal-intrusion interaction plays a central role in this model, the coal geology in Tunguska Basin, i.e. spatial and temporal distribution of coals, coal metamorphism and specifics of the metamorphism at the contact of coals and intrusions, has never been assessed from this prospective. The overall goal of this study is to clarify the role and contribution CO2 of the Tunguska coals to the model. The study suggests that the thickness and distribution of the sills within the coal-bearing successions at most minimally influence the overall metamorphic grade of the coals in Tunguska Basin. The age of the explosion pipes that delivered CO2 into the atmosphere most probably is early Triassic to Jurassic-early Cretaceous. The low degree of metamorphism driven by the magmatism, questions estimates of the amount of sediment-derived CO2 generated that could have influenced or driven the PTB extinction. Furthermore, as a mechanism to deliver such gases to the atmosphere, the explosion pipes post-date the extinction.