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| Titel |
The Late Ordovician crisis: the Large Igneous Province hypothesis tested by global carbon cycle modeling. |
| VerfasserIn |
Vincent Lefebvre, Thomas Servais, Louis Francois, Olivier Averbuch |
| 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 |
250037053
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| Zusammenfassung |
| The causes of the well-known Late Ordovician-Hirnantian glaciation remain largely
debated. This global cooling event is generally attributed to a severe decrease of
atmospheric pCO2 during a time of general greenhouse climate but its duration is not
fully determined. The climate perturbation is synchronous with one of the biggest
biotic crisis of the Earth history. Some authors have shown that, considering the
Ashgillian paleogeography, a drop in pCO2 below a threshold of 8x to 10x PAL (Present
Atmospheric Level) may induce a decrease in temperature in high latitudes so that the
installation of an ice-sheet on Gondwana could be possible. Such a process requires an
intensification of silicate weathering and/or organic carbon burial that are the two major
processes potentially driving a decrease in atmospheric pCO2 at the geologic time
scale.
The Late Ordovician is known to be a period of high mantellic activity marked
by a lack of reversal magnetic field and high volcanic activity. Barnes (2004) and
Courtillot and Olson (2007) link this process to a superplume event that may give rise to
continental basalt flooding. In the present study, we tested this hypothesis with a
global carbon cycle numerical box-model coupled with an Energy Balance Climate
Model. The Model is an upgrade of that used by Grard et al. (2005) to simulate the
environmental impact of the Siberian traps at the P/T boundary. The configuration of
the box-model has been set using the Late Ordovician paleogeography. In each
oceanic box, the model calculates the evolution of carbon, phosphorus and oxygen
concentrations and alkalinity. It also calculates atmospheric pCO2, atmospheric and oceanic
δ13C.
We tested different scenarios of Large Igneous Province (LIP) emplacements and organic
carbon cycle interactions simulating atmospheric pCO2 drops of amplitude large enough to
produce the Hirnantian glaciation. We show that the hypothesis of low latitude LIP well
accounts for the Late Ordovician climate perturbations with a global warming event (the
Boda Event of Fortey and Cocks, 2005) prior to the development of the Hirnantian maximum
cooling. Our simulations furthermore show that a 600 000 km2 continental trap localized at
the equator is the minimum configuration required to reach the 8x PAL atmospheric pCO2
threshold. |
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