Erosion regime and climate of the Himalayan basin during Neogene as recorded in the Bengal fan

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Author(s): France-Lanord, C.; Galy, A.; Galy, V.; Spiess, V.
Author Affiliation(s): Primary:
Université Lorraine, CNRS, Centre de Recherches Pétrographiques et Géochimiques, Vandoeuvre les Nancy, France
Woods Hole Oceanographic Institution-Marine Chemistry & Geochemistry, Woods Hole, MA, United States
University of Bremen, Bremen, Germany
Volume Title: AGU 2018 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2018; American Geophysical Union 2018 fall meeting, Washington, DC, Dec. 10-14, 2018. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: In Himalaya, the monsoon precipitations and tectonic exert a primary control on erosion. Monsoon intensity acts on the extension of the glacier cover, landslide activity, river incision, vegetation cover, and export of sediments towards the floodplain. The monsoon also exerts a primary control on the chemical erosion as weathering rates are limited by transport efficiency. IODP Expedition 354 drilled the Bengal fan (France-Lanord et al. 2016) generated a record of Himalayan erosion over the Neogene and Quaternary. Most of the sediments composing the fan are turbidites issued from the Ganga-Brahmaputra delta and northern Bengal shelf. Turbiditic deposition being discontinuous, the Expedition 354 drilled an E-W transect of seven sites in order to capture as much as possible the displacement of the depocenter. Turbiditic sediments show mineralogical, geochemical and isotopic characteristics which reveal a close analogy with the modern Ganga-Brahmaputra sediments. Internal variability reveals that turbidites are not permanently a mixing of both rivers. There are evidences during the Quaternary that Brahmaputra was for some periods the only source of the turbidites. Major and trace element geochemistry show relatively stable compositions throughout the Neogene and Quaternary. They reveal a very weak regime of chemical weathering with no significant variation through time. Concentrations in mobile elements such as Na and K relative to Al are significantly higher than in modern sediments suggesting that weathering or soil erosion is amplified in the modern time. The record of detrital carbonate deposition shows variations with higher concentrations during the Miocene then falling concentrations during the Plio-Pleistocene. This suggests either a change in the exposition of Tethyan series in Himalaya or significantly lower chemical weathering during Miocene. Overall, the record of erosion at 8°N reveals a relatively stable erosion regime dominated by physical erosion. These observations combined with the reconstitution of paleo-precipitation δD (V. Galy et al., this session) suggest that since 20 Ma the Himalaya was exposed to a monsoonal climate i.e. a highly seasonal climate able to ensure high physical erosion.
Year of Publication: 2018
Research Program: IODP2 International Ocean Discovery Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Bay of Bengal; Bengal Fan; Cenozoic; Climate change; Expedition 354; Himalayan Orogeny; Indian Ocean; International Ocean Discovery Program; Lithostratigraphy; Neogene; Paleoclimatology; Paleoecology; Paleoenvironment; Tertiary
Coordinates: N080023 N080026 E0884432 E0855058
Record ID: 2019040316
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