Among regions of the world where tectonics and climate interact, southern Asia appears to illustrate the possible influences of one on the other more dramatically than in any other region. The high elevation of the Tibetan Plateau and the abrupt rise of the Himalayan barrier profoundly affected both the temperature structure of the atmosphere responsible for the seasonal winds and the localisation of precipitation that characterise the Asian monsoon (Molnar et al. 2010; Boos & Kuang 2011). Concurrently, monsoonal precipitation along the Himalaya generated one of most important erosional flux of the planet. This surface mass transfer acted on the thermal structure and the stress field of the range, and partly determined its morphology (e.g. Avouac & Burov, 1996). Finally, erosional processes participated in the global drawdown of atmospheric CO2 responsible for the Cenozoic global cooling (fig. 1-2) through organic carbon burial and silicate weathering (Raymo and Ruddiman, 1992; France-Lanord and Derry, 1997). Yet if the Tibetan Plateau and the Himalaya have influenced climate during Cenozoic time, the actual evidence suggesting such an influence is wholly inadequate to understand quantitatively how the development of these geographical features have done so. This is mostly due to the fact that direct records of the erosion of the range are rare or temporally limited so there is no consensus on the mass accumulation rate generated by Tibet-Himalayan erosion to date (Clift. 2006). Due to the lack of an adequate sedimentary archive, the Himalayan evolution before the late Miocene is essentially unknown.
The Himal-Fan proposal builds on IODP Expedition 354 (Feb-Mar 2015) that drilled the Bengal Fan as a direct record of the erosion history of the Himalaya (France-Lanord, Spiess, et al. 2016). Primary data include accumulation rates in the fan and core’s sedimentological and geochemical characteristics to trace the geological formations exposed to erosion, and their exhumation rate, weathering, and environmental conditions in the continental basin. Exp. 354 drilled 3 deep sites and 4 shallow sites along a 320 km-long E-W transect across the Bengal Fan at 8°N (fig 3). They compose a 2D overview of the primarily turbiditic depositional system, comprising the Bengal deep sea fan. Exp. 354 has extended the record of early fan deposition by 10 Ma to the MioceneOligocene boundary. It not only collected the first complete Neogene record of Himalayan erosion but also gathered data that will allow the reconstruction of the growth rate of the fan through time. It also cored sediments affected by minimum diagenesis compared to any foreland basin record for which Miocene sediments were buried down to 3-4 km.
This proposal aims to improve our understanding of the Himalayan tectonic construction and its coupling with regional and global climate. Combining Exp. 354 archives, and detailed seismic datasets imaging the fan, it will quantify at different time scales the Himalayan erosion and deposition fluxes, and analyse the response of erosion to tectonic and climate changes. The questions can be rationalised in 3 main issues related to nested temporal windows that are developed bellow, before presenting the Bengal fan and it’s IODP record.