Australia: The Land Where Time Began

A biography of the Australian continent 

End Permian Mass Extinction Confirmed to have Resulted from Voluminous Magmatism Before, During and After Extinction Event

The mass extinction event at the close of the Permian was the most severe of the Phanerozoic with 90 % of marine species and 75 % of terrestrial species going extinct in a maximum of 61,000 ± 48,000 years. The Siberian Traps Large Igneous Province (LIP) was known to have been emplaced around the time of the end-Permian mass extinction event, which was the most voluminous continental eruption since animals arose, has long been suspected of being involved to some extent in the mass extinction event. It has been hypothesised that magmatism rapidly injected massive amounts of greenhouse gasses into the atmosphere which resulted in the driving of climate change which subsequently destabilised the biosphere. To establish a causal link between the magmatism and the mass extinction event depends critically on the accuracy and precision of the relative timing of the 2 events and flux of magma. New U/Pb dates on the lava flows of the Siberian Traps LIP, sills and rocks that were explosively erupted indicate:

1.      About ⅔ of the of the lava/pyroclastic volume was erupted over about 300,000 years, before and concurrent with the mass extinction event of the end-Permian;

2.      The balance of the lavas continued to erupt for at least 500,000 years following the end of the extinction event; and

3.      Emplacement of sills into the shallow crust on a massive scale began concomitant with the mass extinction event, continuing for at least 500,000 years into the Early Triassic.

Burgess and Bowring suggest this age model is consistent with the magmatism of the Siberian traps LIP being a trigger for the mass extinction event of the end-Permian and suggest there was a role for the magmatism in the suppression of biotic recovery post extinction.

Conclusion

Extremely rapid injection of a large volume of carbon that is isotopically light in the form of methane/carbon dioxide into the ocean/atmosphere system, though conjectural, is favoured as a cause of the end-Permian mass extinction event which resulted in hypercapnia (retention of carbon dioxide in the blood), low ocean pH, a calcification crisis and a rise in the temperature of the atmosphere and the ocean. The short time scale of environmental and biotic response requires a source that is capable of generating immense greenhouse gas volumes over short time scales, though the source, isotopic composition and the volume of carbon that is injected, remain speculative.  According to Burges & Bowring their study has demonstrated robust synchrony between the end-Permian mass extinction event and magmatism of the Siberian Traps LIP at the level of ~0.04% or better, as well as lava and pyroclastic eruptions that predate the onset of the extinction event by 300,000 ± 126,000 years, would permit a causal connection. Also, ⅔ of an estimated 4 x 10⁶ km³ of magma were erupted/emplaced over this 300,000 year interval, prior to and during the mass extinction interval.

It is suggested by the relative timing of the voluminous magmatism and the mass extinction event, and the greenhouse gas generating potential, that the most severe extinction event that occurred in the Phanerozoic is inescapably related to a period of high magmatic flux from the Siberian Traps LIP. Burgess and Bowring suggest that as the result of recent improvements in the accuracy and precision to which the time scales of LIP eruptions/emplacement are known, there is an intriguing pattern that has emerged, with magmatism occurring long after a punctuated instance of extinction, as well as before and during the event. It is suggested by the striking disparity between the 2 events that an aliquot of the total magma that was erupted/emplaced in a very restricted interval might be more important than the enormous total volume of LIP magmas. Burgess and Bowring suggest that early intrusion and transit through a basin that was volatile rich, and that was untapped, may be this critical aliquot. There is suggested to be a need to repopulate the models of the atmospheric change that resulted from magmatism, as a result of ever-improving geochronology, palaeontology, and proxy stratigraphic constraints, and to re-evaluate the detailed relationship between magmatism and biotic crisis.

Sources & Further reading

1. Burgess, S. D. and S. A. Bowring (2015). High-precision geochronology confirms voluminous magmatism before, during, and after Earth’s most severe extinction.