Mathematics – Logic
Scientific paper
Nov 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007e%26psl.263....1c&link_type=abstract
Earth and Planetary Science Letters, Volume 263, Issue 1-2, p. 1-15.
Mathematics
Logic
27
Scientific paper
Most mass extinctions coincide in time with outpourings of continental flood basalts (CFB). Some 20 years ago, it was shown [Courtillot, V., Besse, J., Vandamme, D., Montigny, R., Jaeger, J.-J., Cappetta, H., 1986. Deccan flood basalts at the Cretaceous/Tertiary boundary? Earth Planet. Sci. Lett. 80, 361 374; Courtillot, V., Feraud, G., Maluski, H., Vandamme, D., Moreau, M.G., Besse, J., 1988. Deccan flood basalts and the Cretaceous/Tertiary boundary. Nature 333, 843 846; Duncan, R.A., Pyle, D.G., 1988. Rapid eruption of the Deccan flood basalts at the Cretaceous/Tertiary boundary. Nature 333 841 843] that the age of the Deccan traps was close to the Cretaceous Tertiary (KT) boundary and its duration under 1 Myr. We have undertaken a new geochronological study, using the (unconventional) 40K 40Ar Cassignol Gillot technique which is particularly well suited to the potassium-poor Deccan lavas. The mean of 4 determinations from the topmost (Ambenali and Mahabaleshwar) Formations is 64.5 ± 0.6 Ma. They straddle the C29r/C29n reversal boundary for which they provide a new constraint. The mean age of 3 determinations from the oldest (Jawhar) Formation is 64.8 ± 0.6 Ma. The difference in age between top and bottom of a 3500 m composite section, probably comprising 80% of the total Deccan volume, is statistically insignificant, with the overall mean age being 64.7 ± 0.6 Ma (N = 7). Our results are consistent with the most recent 40Ar/39Ar determinations [Knight, K.B., Renne, P.R., Halkett, A., White, N., 2003. 40Ar/ 39Ar dating of the Rajahmundry Traps, eastern India and their relationship to the Deccan traps. Earth Planet. Sci. Lett. 208, 85 99; Knight, K.B., Renne, P.R., Baker, J., Waight, T., White, N., 2005. Reply to ‘40Ar/39Ar dating of the Rajahmundry Traps, Eastern India and their relationship to the Deccan Traps: Discussion’ by A.K. Baksi. Earth Planet. Sci. Lett. 239, 374 382], confirming that there should be no systematic difference between the two methods when they are used in an optimal way. An earlier, smaller but significant, pulse of volcanism between 68 and 67 Ma, extending over at least 500 km in latitude in the northern part of the Deccan CFB has also been identified. After 2 to 3 Ma of quiescence, the second, major phase of volcanism occurred near 65 Ma, expanding over most of the area covered by the first pulse and another 500 km to the South, consistent with drift of India by 300 to 450 km at ˜ 150 mm/yr during the quiescence period. New paleontological data from the remote Rajahmundry section [Keller, G., Adatte, T., Gardin, S., Bartolini, A., Bajpai, S., Humler, E., in prep. The Cretaceous Tertiary boundary in Deccan Traps of the Krishna Godavari Basin of southeastern India. EPSL to be submitted] suggest that this second pulse can itself be divided into two major pulses, one starting in C29r and ending at the KT boundary, the second starting in the upper part of C29r and ending within C29n.
Bajpai Sunil
Chenet Anne-Lise
Courtillot Vincent
Fluteau Frédéric
Quidelleur Xavier
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