THE SIBERIAN TRAPS VOLCANISM AND ITS ENVIRONMENTAL IMPACT THROUGH PERMIAN-TRIASSIC TIMES

The Siberian Traps are the world’s largest continental flood basalt province encompassing an area of some 5 million km². The bulk of this volcanism occurred synchronous with the most severe extinction on Earth at the end of the Permian Period, some 251 million years ago. A characteristic feature of the extinction was its protracted nature, with a long period of oceanic anoxia. Sustained recovery began primarily in the early part of the Middle Triassic, some 4 to 8 million years after the extinction itself. This apparent delay of biological renewal could reflect the time scale necessary for reintegration of ecosystems, or reflect persistently unfavourable environmental conditions through part or all of the Early Triassic.

Widespread basaltic and rhyolitic volcanic sequences are buried within northeast–southwest trending grabens in the southern Urals. Extensive drilling, seismic studies and rock exposures reveal that the basaltic volcanic sequences cut through rhyolites and extend over a region approximately 41,000 km² and are up to 2.0 km thick towards the centres of the grabens, making this a substantial volcanic province. New ⁴⁰Ar/³⁹Ar age determinations on these basaltic rocks are ~245 Ma whereas rhyolites provide zircon U/Pb ages of 250.9 ± 0.2 and 250.7 ± 0.7 Ma (2σ) demonstrating that volcanism in SE-Siberia occurred in at least two stages. We provide here the first evidence for Permo-Triassic bimodal volcanism in Siberia demonstrating that the basalt volcanism is not related to the main activity of the Siberian Traps. The Permo-Triassic volcanic activity recorded in the southern Urals may have contributed and maintained environmental stress throughout and after the main extinction well into the Triassic. This volcanism may have provided a potential source for CO₂, which is recorded in a series of negative and positive excursions that continued throughout the early part of the Triassic.