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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, B04101, doi:10.1029/2006JB004635, 2008

Determination of rapid Deccan eruptions across the Cretaceous-Tertiary boundary using paleomagnetic secular variation: Results from a 1200-m-thick section in the Mahabaleshwar escarpment

Anne-Lise Chenet

Laboratoire de Paléomagnétisme, IPGP, Paris, France


Frédéric Fluteau

Laboratoire de Paléomagnétisme, IPGP, Paris, France


Vincent Courtillot

Laboratoire de Paléomagnétisme, IPGP, Paris, France


Martine Gérard

Institut de Recherche pour le Développement and IMPMC, Paris, France


K. V. Subbarao

Centre for Earth Science and Space Sciences, University of Hyderabad, Hyderabad, India


Abstract

Flow-by-flow reanalysis of paleomagnetic directions in two sections of the Mahabaleshwar escarpment, coupled with analysis of intertrappean alteration levels shows that volcanism spanned a much shorter time than previously realized. The sections comprise the upper part of magnetic chron C29r, transitional directions and the lowermost part of C29n. Lack of paleosecular variation allows identification of four directional groups, implying very large (40 to 180 m thick) single eruptive events (SEEs) having occurred in a few decades. Paleomagnetism allows temporal constraints upon the formation of 9 out of 23 thin red bole levels found in the sections to no more than a few decades; the two thickest altered layers could have formed in 1 to 50 ka. The typical volumes of SEEs (corresponding to magnetic directional groups) are estimated at 3000 to 20,000 km3, with flux rates ∼100 km3 a−1, having lasted for decades. Flood basalt emission can be translated into SO2 injection rates of several Gt a−1, which could have been the main agent of environmental change. The total volume of SO2 emitted by the larger SEEs could be on the order of that released by the Chicxulub impact. Moreover, each SEE may have injected 10 to 100 times more SO2 in the atmosphere than the deleterious 1783 Laki eruption. The detailed time sequence of SEEs appears to be the key feature having controlled the extent of climate change. If several SEEs erupted in a short sequence (compared to the equilibration time of the ocean), they could have generated a runaway effect leading to mass extinction.

Received 18 July 2006; accepted 17 December 2007; published 30 April 2008.

Keywords: Deccan Traps; paleomagnetism; eruptive sequence.

Index Terms: 1527 Geomagnetism and Paleomagnetism: Paleomagnetism applied to geologic processes; 8408 Volcanology: Volcano/climate interactions (1605, 3309); 4901 Paleoceanography: Abrupt/rapid climate change (1605); 8450 Volcanology: Planetary volcanism (5480, 6063, 8148).

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Citation: Chenet, A.-L., F. Fluteau, V. Courtillot, M. Gérard, and K. V. Subbarao (2008), Determination of rapid Deccan eruptions across the Cretaceous-Tertiary boundary using paleomagnetic secular variation: Results from a 1200-m-thick section in the Mahabaleshwar escarpment, J. Geophys. Res., 113, B04101, doi:10.1029/2006JB004635.