Environmental Engineering Reference
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(IETM), explaining both the subsequent global warming and a negative excursion
in carbon isotopes. Svensen et al .( 2007 ) proposed that complexes intruded into the
Karoo sedimentary basin would have emitted 27,400 Gt of CO 2 , and contributed to
the global warming observed during the Toarcian (disputed by Gröcke et al .,
2009 ). Ganino and Arndt ( 2009 ) estimated that the release of sediment-derived
CO 2 would have been from 3.6 to 8.6 times larger than that due to magma
degassing in the Emeishan Traps (
258 Ma). Finally, heating of organic-rich
shale and petroleum bearing evaporites by the Siberian Traps would have generated
100,000 Gt of CO 2 , explaining global warming at the Permo-Triassic boundary
and carbon isotopic excursions. The amounts of thermogenic gases are generally
extrapolated from the analyses of a small number of outcropping sections of
sedimentary formations intruded by dikes and sills. This remains dif
~
cult, due
to the size of the intrusive systems and potential lateral variability of intruded
formations. Also, the precise tempo of emission of gases needs to be evaluated.
With the exception of the NAIP (relatively well constrained by palynozones
-
Svensen et al ., 2004 ), the ages of thermogenic events are known only through
isotopic dating of volcanic intrusive complexes. Stratigraphic relationships within
dike and sill complexes are not as clear as in a sequence of lava
ows.
15.6 Summary
Thermal/compositional plumes, a component of convective motions within the
Earth
'
s mantle, are considered to be responsible for exceptional volcanism,
and also to play a role in localizing continental stretching and breakup. The large
mushroom-shaped heads of plumes would generate LIPs. The past ~ 35 years
have seen tremendous advances in our understanding of the links between this
LIP volcanism and mass extinctions.
The KTB extinction has been the main focus of attention, following the
1980 paper suggesting the impact of an asteroid and the mid-1980s papers suggesting
that Deccan volcanism could have been a major player. In order to establish a more
general interpretation, other
flood basalts, impact craters and mass extinction events
had to be studied. Successive reviews of available age determinations of the
three kinds of events strengthened the idea that impacts were the exception and
ood
basalt volcanism the general rule. The correlation is now such that the association
of LIPs with mass extinctions is unavoidable. Only the KTB has convincing
evidence for co-eval impact and volcanism at the time of extinction.
Successive advances have helped in constraining the timing of volcanism,
based on bringing together results from many disciplines. Our group has focused
on paleomagnetism, paleontology and geochronology. This has led to a picture
of several embedded timescales. In many LIPs, the total duration between the
rst
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