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Australia: The Land Where Time Began |
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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.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |