ProjectA4

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<h3>Background</h3>
<h3>Background</h3>
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[[image:Fig1_A4.jpg|left|thumb|350px|Figure 1. Correlation of mass extinction events with very large mafic magma eruptions]]
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There is considerable debate on the causes of the biological mass extinction events recognized in the Phanerozoic fossil record. There is consensus that extinctions reflect events of dramatic climate change but the underlying causes of the change remain controversial. Correlations between the mass extinctions and large volume volcanic eruptions (Fig. 1 from Courtillot & Renne, 2003) together with known temperature/climate modification effects of some historical eruptions such as Pinatubo (1991-1992) and Laki (1783-1784) are powerful arguments for a volcanic cause of many of the extinction events. To strengthen and test this hypothesis, large volcanic events have to be investigated in detail to establish (a) the precise timing of the volcanism, (b) volume-duration relationship during the volcanic event and (c) climate change modelling. Detailed results from one such study (Chenet et al, in press) on the Deccan Flood basaltic sequence, which correlates with the large extinction event at the K-T boundary, have shown that flow-by-flow palaeomagnetic sampling of well-characterized stratigraphic sequences allow geomagnetic secular variation data to be recovered from the lava flows. The secular variation can be used as a time proxy which has allowed considerable refinement of the details of the emplacement history of the volcanic sequence, in particular volume-duration relationships. Together with data from red boles intercalated in the lava sequence, results indicate that the Deccan was emplaced as a small number of discrete large-volume short-lived pulses without significant quiescence between them. Gas emissions (largely SO2) of each pulse are of the same order as those proposed for the Chixculub impact, the rival hypothesis for the K-T extinction. These data are strongly suggestive of Deccan volcanism having a significant impact on Earth‟s climate.</p>
There is considerable debate on the causes of the biological mass extinction events recognized in the Phanerozoic fossil record. There is consensus that extinctions reflect events of dramatic climate change but the underlying causes of the change remain controversial. Correlations between the mass extinctions and large volume volcanic eruptions (Fig. 1 from Courtillot & Renne, 2003) together with known temperature/climate modification effects of some historical eruptions such as Pinatubo (1991-1992) and Laki (1783-1784) are powerful arguments for a volcanic cause of many of the extinction events. To strengthen and test this hypothesis, large volcanic events have to be investigated in detail to establish (a) the precise timing of the volcanism, (b) volume-duration relationship during the volcanic event and (c) climate change modelling. Detailed results from one such study (Chenet et al, in press) on the Deccan Flood basaltic sequence, which correlates with the large extinction event at the K-T boundary, have shown that flow-by-flow palaeomagnetic sampling of well-characterized stratigraphic sequences allow geomagnetic secular variation data to be recovered from the lava flows. The secular variation can be used as a time proxy which has allowed considerable refinement of the details of the emplacement history of the volcanic sequence, in particular volume-duration relationships. Together with data from red boles intercalated in the lava sequence, results indicate that the Deccan was emplaced as a small number of discrete large-volume short-lived pulses without significant quiescence between them. Gas emissions (largely SO2) of each pulse are of the same order as those proposed for the Chixculub impact, the rival hypothesis for the K-T extinction. These data are strongly suggestive of Deccan volcanism having a significant impact on Earth‟s climate.</p>

Revision as of 15:46, 2 July 2009

Contents

Project A4: Large igneous provinces, impacts and climate change

French pi: F. Fluteau (with V. Courtillot)
South African pi: G. Marsh

Project Participants

France:

V. Courtillot, F. Fluteau, J. Besse, X. Quidelleur, G. Delpech, C Jaupart, M. Gérard, H. Bouquerel

South Africa:

J. Marsh, M. Watkeys, M. Klausen, A. Duncan, plus one or two Msc or PhD students to be determined

Project Summary

The project focuses on detailed flow-by-flow sampling for palaeomagnetic secular variation studies on two well-characterized Karoo volcanic sequences (a) The low-Ti Oxbow sequence of northern Lesotho, and (b) the high-Ti Olifants River sequence of northern Lebombo. Palaeomagnetic measurements will be done at IPGP and will be complemented by K/Ar and 40Ar/39Ar dating (IPGP) and additional geochemical studies (South Africa) where necessary. The project goal is to construct a refined model for the emplacement of the Karoo volcanic sequences with particular emphasis on volumes and duration of eruptive episodes (in particular identification of short large pulses) and their impact on climate modifications with implications for the end-Pliensbachian extinction. This will be compared to the case of the Deccan volcanics and KT mass extinction.

Background

Figure 1. Correlation of mass extinction events with very large mafic magma eruptions

There is considerable debate on the causes of the biological mass extinction events recognized in the Phanerozoic fossil record. There is consensus that extinctions reflect events of dramatic climate change but the underlying causes of the change remain controversial. Correlations between the mass extinctions and large volume volcanic eruptions (Fig. 1 from Courtillot & Renne, 2003) together with known temperature/climate modification effects of some historical eruptions such as Pinatubo (1991-1992) and Laki (1783-1784) are powerful arguments for a volcanic cause of many of the extinction events. To strengthen and test this hypothesis, large volcanic events have to be investigated in detail to establish (a) the precise timing of the volcanism, (b) volume-duration relationship during the volcanic event and (c) climate change modelling. Detailed results from one such study (Chenet et al, in press) on the Deccan Flood basaltic sequence, which correlates with the large extinction event at the K-T boundary, have shown that flow-by-flow palaeomagnetic sampling of well-characterized stratigraphic sequences allow geomagnetic secular variation data to be recovered from the lava flows. The secular variation can be used as a time proxy which has allowed considerable refinement of the details of the emplacement history of the volcanic sequence, in particular volume-duration relationships. Together with data from red boles intercalated in the lava sequence, results indicate that the Deccan was emplaced as a small number of discrete large-volume short-lived pulses without significant quiescence between them. Gas emissions (largely SO2) of each pulse are of the same order as those proposed for the Chixculub impact, the rival hypothesis for the K-T extinction. These data are strongly suggestive of Deccan volcanism having a significant impact on Earth‟s climate.