The Paleogene record of Himalayan erosion: Bengal Basin, Bangladesh

Najman, Y. and Bickle, M. J. and BouDagher-Fadel, M. and Carter, A. and Garzanti, E. and Paul, M. and Wijbrans, J. and Willett, E. and Oliver, G. and Parrish, R. and Akhter, S.H. and Allen, R. and Ando, S. and Chisty, E. and Reisberg, L. and Vezzoli, G. (2008) The Paleogene record of Himalayan erosion: Bengal Basin, Bangladesh. Earth and Planetary Science Letters, 273 (1-2). pp. 1-14. DOI

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A knowledge of Himalayan erosion history is critical to understanding crustal deformation processes, and the proposed link between the orogen's erosion and changes in both global climate and ocean geochemistry. The most commonly quoted age of India-Asia collision is ~ 50 Ma, yet the record of Paleogene Himalayan erosion is scant -- either absent or of low age resolution. We apply biostratigraphic, petrographic, geochemical, isotopic and seismic techniques to Paleogene rocks of the Bengal Basin, Bangladesh, of previously disputed age and provenance. Our data show that the first major input of sands into the basin, in the > 1 km thick deltaic Barail Formation, occurred at 38 Ma. Our biostratigraphic and isotopic mineral ages date the Barail Formation as spanning late Eocene to early Miocene and the provenance data are consistent with its derivation from the Himalaya, but inconsistent with Indian cratonic or Burman margin sources. Detrital mineral lag times show that exhumation of the orogen was rapid by 38 Ma. The identification of sediments shed from the rapidly exhuming southern flanks of the eastern-central Himalaya at 38 Ma, provides a well dated accessible sediment record 17 Myr older than the previously described 21 Ma sediments, in the foreland basin in Nepal. Discovery of Himalayan detritus in the Bengal Basin from 38 Ma: 1) resolves the puzzling discrepancy between the lack of erosional evidence for Paleogene crustal thickening that is recorded in the hinterland; 2) invalidates those previously proposed evidences of diachronous collision which were based on the tenet that Himalayan-derived sediments were deposited earlier in the west than the east; 3) enables models of Himalayan exhumation (e.g. by mid crustal channel flow) to be revised to reflect vigorous erosion and rapid exhumation by 38 Ma, and 4) provides evidence that rapid erosion in the Himalaya was coincident with the marked rise in marine 87Sr/86Sr values since ~ 40 Ma. Whether 38 Ma represents the actual initial onset of vigorous erosion from the southern flanks of the east-central Himalaya, or whether older material was deposited elsewhere, remains an open question.

Item Type: Article
Uncontrolled Keywords: 08AREP; IA57;
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
05 - Petrology - Igneous, Metamorphic and Volcanic Studies
02 - Geodynamics, Geophysics and Tectonics
Divisions: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Journal or Publication Title: Earth and Planetary Science Letters
Volume: 273
Page Range: pp. 1-14
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 26 Mar 2009 17:10
Last Modified: 23 Jul 2013 09:54

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