Flood basalts of Siberian Traps doubled at a stroke

Erupted at the time of the Palaeozoic-Mesozoic boundary, and coinciding with the largest mass extinction during the Phanerozoic, the Siberian Traps are by far the biggest example of flood-basalt volcanism known.  They blanket a huge area of the Siberian Platform.  To the east of their outcrops is a large extensional downwarp, known as the West Siberian Basin, where recent deep drilling has cut through up to 1 km of flood basalts.  Dating samples from 15 boreholes proves that these too are members of the Siberian Trap suite (Reichow, M.K. et al. 2002.  40Ar/39Ar dates from the West Siberian Basin: Siberian flood basalt province doubled.  Science, v. 296, p. 1846-1849).  Combined, the two zones of Siberian Traps represent eruption of around 2.3 million km3 of plume-derived magma at around 250 Ma ago, possibly within 2 or 3 Ma.  Gas release from such a stupendous event is implicated in the Permian-Triassic mass extinction, either through climate change associated with CO2 and SO2, or toxic effects of hydrofluoric acid.  Unlike the end-Triassic and K-T extinctions, no clear evidence has emerged for coincident flood volcanism and major impact at the end of the Palaeozoic Era.  However, the use of tungsten isotopes as “fingerprints” for extraterrestrial debris in boundary sediments may help resolve the issue of whether an impact accompanied the Siberian Traps (see Tungsten and Archaean heavy bombardment, this issue)


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