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| Titel |
Timing of Emeishan magmatic activity and implications for the end-Middle Permian biotic crisis |
| VerfasserIn |
R. Mundil, S. W. Denyszyn, J. G. Shellnutt, A. B. Jost, J. L. Payne, P. R. Renne, B. He, Y. Zhong, Y. Xu |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250064608
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| Zusammenfassung |
| Evidence from high-resolution geochronology combined with fossil records and proxies for
changes in the paleoenvironment suggest that there is a link between large-scale (but
short-term) volcanic events and mass extinctions. Synchroneity has been shown between
large-scale volcanic events and three of the five most severe mass extinctions: the
end-Permian extinction (P-T) coincides with Siberian Traps LIP; the end-Triassic extinction
(Tr-J) with Central Atlantic Magmatic Province; and the end-Cretaceous (K-P) with the
Deccan Traps LIP. Recent studies also show that the magnitude of the extinction is not a
simple function of the size (volume) of the igneous event; rather, the eruption rate and nature
of the host rock that is intruded exert important controls on the rate and magnitude of the
release of gases that affect climate and ocean chemistry. Consequently, high-resolution
geochronological constraints on LIP volcanism, biotic extinctions, and climatic
change are essential to understanding the role of magmatism in these evolutionary
catastrophes.
The end-Guadalupian (latest Middle Permian) extinction event shows a selectivity pattern
similar to the better-studied end-Permian extinction. Single zircon U-Pb ages from
intrusions related to the late Middle Permian ca 260 Ma Emeishan LIP (central
and southwest China) have recently been shown to have intruded within a very
narrow time interval between 260 and 257 Ma, broadly overlapping the timing of
end-Guadalupian biotic change. New zircon U-Pb ages from felsic volcanic rocks overlying
the youngest Emeishan related basalts show that effusive volcanism was terminated
between 258 and 259 Ma, suggesting that the main stage of volcanism was very short.
Unfortunately, 40Ar/39Ar analyses applied to minerals extracted from basalts have proven
notoriously difficult because of thermal overprint in the studied area. Whereas the
timing of Emeishan related magmatic activity is now better constrained by our new
U-Pb zircon analyses, there are so far only few robust geochronologic data from
biostratigraphically constrained sedimentary sequences across the Middle to Late Permian
boundary.
The volume of intrusive and effusive rocks related to the Emeishan LIP is difficult to
reconstruct, but is thought to be significantly smaller than the three LIPs mentioned
above. Consequently, the volume of gas release and its effects on the atmosphere and
hydrosphere may have been not as devastating as during the following three major
extinctions (P-T, Tr-J, K-P). Initial results from stable calcium isotope records in marine
carbonates and conodont microfossils across the Middle to Late Permian boundary
indicate the magnitude of changes in ocean carbonate and redox chemistry was much
smaller than those associated with the subsequent end-Permian mass extinction.
Ongoing research is aimed at corroborating this finding but compromised by the
scarcity of marine sedimentary archives of this age. In addition, our current efforts
concentrate on constructing a robust chronostratigraphic framework for this time interval. |
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