K-Ar Dating and Paleomagnetic Contributions : still more Evidence for the Short Duration of the Deccan Large Igneous Province

Mathematics – Logic

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1100 Geochronology, 1522 Paleomagnetic Secular Variation, 1605 Abrupt/Rapid Climate Change (4901, 8408), 8408 Volcano/Climate Interactions (1605, 3309)

Scientific paper

Particular interest in Continental Flood Basalts (CFBs) comes from the suggestion that they might be associated with mass extinction of species. The most studied case is the Cretaceous-Tertiary boundary (KTB), for which evidence of both impact of an extraterrestrial object and large-scale volcanism has become overwhelming. The problem is to attempt to unravel the respective contributions of these two events to the extinction pattern. We present here evidence for environmental and climatic consequences following the emplacement of the Deccan traps. We report 8 new K-Ar ages obtained in the Orsay geochronological laboratory (France) from samples distributed within the Western Ghats Formations (India). The data are distributed in two groups, revealing two phases of lava emplacement. A first, volumetrically smaller, pulse has been dated at 67.4 ± 1.0 Ma. A second, dominant, event has a mean absolute age of 64.7 ± 0.6 Ma. Individual ages range from 64.1 ± 0.9 Ma to 64.8 ± 0.9 Ma, possibly implying a total duration for the major volcanic phase forming the Western Ghats as short as 500 kyr. This is in agreement with paleomagnetic analyses constructed on all Formations from the Western Ghats. Based on records of secular variation of the geomagnetic field by lava flows, in addition to volcanological constraints, we have been able to reconstruct the eruptive history of the Main Deccan Province. A rather small number of very large volcanic pulses (lasting possibly a few decades) comprising much of the 3000m-thick pile of lava, and the huge amounts of sulfur dioxide which they injected into the atmosphere are most likely a determining factor of a global environmental perturbations incurred at the KTB time.

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