Expedition 354 on the Bengal Fan; a Neogene record of Himalayan erosion

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http://abstractsearch.agu.org/meetings/2017/FM/OS54B-02.html
Author(s): France-Lanord, Christian; Spiess, Volkhard; Schwenk, Tilmann; Klaus, Adam; Galy, Albert
Author Affiliation(s): Primary:
Centre de Recherches Pétrographiques et Géochimiques, Vandoeuvre-Les-Nancy, France
Other:
MARUM-University of Bremen, Germany
Texas A&M University, International Ocean Discovery Program, United States
Volume Title: AGU 2017 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2017; American Geophysical Union 2017 fall meeting, New Orleans, LA, Dec. 11-15, 2017. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Drilling in the Bengal Fan generated a comprehensive record of Himalayan erosion over the Neogene and Quaternary. It documents the interplay between Himalayan tectonic and the monsoon. The fan is predominantly composed of detrital turbiditic sediments originating from Himalayan rivers, and transported through the delta and shelf canyon, supplying turbidity currents loaded with a wide spectrum of grain sizes. Turbiditic deposition makes that record at a given site is discontinuous which was the reason for an E-W transect approach. Exp. 354 drilled seven sites along a 320 km E-W transect at 8°N allowing the restitution of an almost complete record of Himalayan erosion at the scale of the Neogene. In spite of the transect's extension, a long absence of deposition was observed between 0.6 to 1.2 Ma indicating that turbiditic depocenter was derived more to the West for ca. 600 kyr. Turbidites have clear Himalayan origin with close mineralogical and isotopic analogy with those of the modern Ganga-Brahmaputra river sediments. Geochemistry shows relatively stable compositions throughout the Neogene and Quaternary and 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 is amplified in the modern time. Low weathering of the sediments at 8°N indicates that erosion was dominated by physical processes and that transport is rapid enough to prevent evolution of particles in the floodplain. In the modern Himalaya, low weathering is achieved primarily by landslides and rapid transfer through the floodplain, i.e. limited recycling of sediment deposited in the floodplain. Both processes are favored by the seasonality and the intensity of the monsoon. Although relatively stable, source tracers such as Sr-Nd isotopic compositions, and detrital carbonate compositions show organized variations with time. They imply that exposure to erosion of the different Himalayan formations has evolved as a result of the evolution of the thrusting structures. Data suggest that (1) Tethys Himalaya exposure to erosion was higher during Miocene than after 5 Ma and (2) that the exhumation of the Lesser Himalaya was initiated around 8 Ma.
Year of Publication: 2017
Research Program: IODP2 International Ocean Discovery Program
Key Words: 07 Marine Geology and Oceanography; Asia; Bay of Bengal; Bengal Fan; Cenozoic; Expedition 354; Himalayas; Indian Ocean; International Ocean Discovery Program; Marine sediments; Neogene; Sediments; Tertiary
Coordinates: N080023 N080026 E0884432 E0855058
Record ID: 2019025818
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