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10Be - Sr - Nd applied on Bengal fan Expedition 353-354: A record of Late Cenozoic Himalayan erosion

Abstract : Global records of erosion have led to conjecture that the Quaternary climatic transition was linked to an acceleration of erosion on Earth (Zhang et al. 2001, Herman et al. 2013). However, the reality of this increase of the erosion rates remains debated (e.g. Willenbring and von Blanckenburg 2010). In order to implement the debate at the scale of a major orogen, we have applied to the Himalaya a distinct approach, which is not affected by the same possible bias than for previously developed methods. We present a new record of Himalayan erosion from IODP drilled cores in the Bengal fan. The fan mainly consists of sand-rich turbidites that originate from sediments eroded in the Himalaya and transported by the Ganga and the Brahmaputra since at least 20 Ma onwards. IODP Expeditions 353 and 354 (Clemens et al. 2016, France-Lanord et al. 2016) recently drilled 1 site at 14°N and a transect of seven sites at 8°N in the fan. These cores were dated by magnetostratigraphy and biostratigraphy. The provenance of Plio-Pleistocene sediments was traced using 87 Sr/ 86 Sr and 143 Nd/ 144 Nd ratios from bulk silicates. Contrasted isotopic signatures characterize the Himalayan formations and the Transhimalaya, which results in distinct compositions for modern Ganga and Brahmaputra river sediments. Sr and Nd isotopic ratios range from 0.72 to 0.76 and from-17 to-13. They imply significant variations in the provenance mixture between Himalayan and Transhimalayan formations since 6 Ma. In particular, we notice a higher proportion of Transhimalayan provenance for the last 0.2 Ma. Past erosion rates (mean values over timescales of ~1 kyr) were traced using in-situ cosmogenic 10 Be paleo-concentrations in the quartz of the sandy 75-250 μm fraction (e.g. Charreau et al. 2011). 10 Be paleo-concentrations vary in a range similar to the concentrations measured on the Brahmaputra and Ganga modern sands (Lupker et al. 2012; 2017). Although paleo-concentrations appear rather variable before 2 Ma and steadier afterwards, the time-averaged signal is relatively constant over the whole Plio-Pleistocene period and highlights a steadiness of the Himalayan erosion rates. Even if dominant sources of sediments seem to fluctuate in the Brahmaputra-Ganga watershed, our dataset suggests that the Himalayan erosion may not have been sensitive to climate cooling at the Quaternary transition, and that its erosion patterns may be mainly controlled by regional tectonics. References Charreau J, Blard PH, Puchol N, Avouac JP, Lallier-Vergès E, Bourlès D, Braucher R, Gallaud A, Finkel R, Jolivet M, Chen Y, Roy P (2011) Paleo-erosion rates in Central Asia since 9 Ma: A transient increase at the onset of Quaternary glaciations? Earth Planet Sci Lett 304: 85-92. (2013) Worldwide acceleration of mountain erosion under a cooling climate. Nature 504: 423-426. Lupker M, Blard PH, Lavé J, France-Lanord C, Leanni L, Puchol N, Charreau J, Bourlès D (2012) 10Be-derived Himalayan denudation rates and sediment budgets in the Ganga basin. Earth Planet Sci Lett 333-334: 146-156.
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https://hal.archives-ouvertes.fr/hal-02328670
Contributor : Christian France-Lanord <>
Submitted on : Wednesday, October 23, 2019 - 11:52:33 AM
Last modification on : Thursday, November 21, 2019 - 4:22:12 PM

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Sébastien Lénard, Jérôme Lavé, C. France-Lanord. 10Be - Sr - Nd applied on Bengal fan Expedition 353-354: A record of Late Cenozoic Himalayan erosion. 33rd Himalaya-Karakorum-Tibet workshop, Sep 2018, Lausanne, Switzerland. ⟨hal-02328670⟩

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