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| Titel |
Emeishan volcanism and the end-Guadalupian extinction: New U-Pb TIMS ages |
| VerfasserIn |
Roland Mundil, Steve Denyszyn, Bin He, Ian Metcalfe, Xu Yigang |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250034811
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| Zusammenfassung |
| High-resolution geochronology with an age resolution at the permil level is instrumental in
testing proposed causal links between continental-scale, short-term volcanic events and
environmental crises that affect life globally. Synchroneity with large-scale volcanic events
has been shown for three of the five most severe extinctions, namely the end-Permian
extinction coinciding with Siberian Trapp volcanism, the end-Triassic extinction with Central
Atlantic Magmatic Province) volcanism and the end-Cretaceous with Deccan Trapp
volcanism. Recent studies also show that the magnitude of the extinction is not solely a
function of the size (volume) of the volcanic event but more importantly of the eruption rate
and also the nature of the host rock that is intruded, and the resulting reactions and release of
gases that can affect climate.
The end-Guadalupian (end Middle Permian, ca 260 Ma) biotic crisis has traditionally not
been included in the “big five” mass extinctions, possibly because of its close proximity in
time to the end-Permian event, although its magnitude (in terms of total extinction rate) is
comparable to the three most severe extinctions (end-Ordovician, end-Permian,
end-Cretaceous). As a result, research of the end-Guadalupian event has so far been
neglected and its timing as well as the temporal relation to the Emeishan volcanic
province in western China is as yet not fully studied. Geochronological data are so
far mostly based on ambiguous 40Ar/39Ar analyses of commonly altered basaltic
products and U-Pb zircon analyses on felsic products using micro-beam techniques
that typically result in radio-isotopic ages with percent-level uncertainty, and thus
insufficient for high-resolution correlations of events. In addition, no precise and accurate
radio-isotopic data exist from this time period so that evolutionary events (extinction and
recovery) on land and in the ocean are notoriously difficult to correlate though
biostratigraphic records are available from numerous sedimentary archives. A further
complication arises from the severe tectonic (and resulting thermal) overprint, due to the
closure of the Tethys and the collision of the Indian plate with Asia, of most of
the area where Emeishan volcanic products are exposed. Also, currently existing
paleo-environmental data are scarce and insufficient for testing this hypothesis
with confidence, because studies using stable isotopes as proxies are restricted
to short profiles from only a few sites. Therefore, fundamental questions remain
unanswered.
We present new data U-Pb IDTIMS ages with permil-level resolution that constrain the
timing of Emeishan volcanism and the timing of biotic events recorded in sediments. In
detail, U-Pb results are from felsic intercalations within late stage Emeishan products and
biostratigaphically calibrated marine sedimentary sections in southwestern and central China
as well as thick tuffs within terrestrial sections from the Bowen Basin in eastern Australia.
There is also great potential for obtaining precise U-Pb age results on volcanic products with
basaltic composition using the accessory mineral baddeleyite the occurrence of which we
have already confirmed. Geochronological and geochemical research is complemented with
paleo-enviromental studies and biostratigraphy. We expect that through integration of
U-Pb and 40Ar/39Ar geochronology with chemo- and biostratigraphy, the time scale
of the Middle through Late Permian will be greatly improved and will lead to a
more realistic evaluation of potential causes for the biotic crisis and its aftermath. |
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