Among regions of the world where tectonics and climate interact, southern Asia seems to illustrate the possible influences of one on the other more dramatically than any other region. The high elevation of the Tibetan Plateau and the rapid rise from the lowlands of northern India across the Himalaya profoundly affect both the average temperature structure of the atmosphere responsible for the seasonal winds and the localization of precipitation that characterize the south Asian monsoon. Concurrently, large seasonal variations in precipitation along the Himalaya affect erosion rates. Yet if the Tibetan Plateau and the Himalaya have influenced climate during Cenozoic time, the evidence suggesting such an influence is wholly inadequate to understand quantitatively how the development of these geographical features have done so.

Expedition 354 is designed to obtain data that can not only test proposed hypothetical links between climate and tectonics but also provide new data not easily anticipated but relevant to understanding a number of processes in the Earth. This expedition in the Bay of Bengal focuses on its record of the erosional history of the Himalaya and on the development of the Asian monsoon over Cenozoic time. Because geology lacks the tools for determining paleoelevations except in unusual and ideal circumstances, the sedimentary record of material eroded from a mountain belt holds the least ambiguous record of its paleotopography. Roughly 80% of the material eroded from the Himalaya has been deposited in the Bay of Bengal, making it the most complete record.

During Expedition 354, six sites will be drilled in an east–west transect at 8°N (Figs. F1, F2), including

  • One deep site to ~1500 m to reach prefan deposits (Site MBF-3A),
  • Two sites to ~900 m (Sites MBF-1A and MBF-2A) to recover sediment at least as old as 10–12 m.y. to study Neogene fan evolution and the impact of the monsoonal system on sediment supply and flux, and
  • Three sites to ~300 m to recover a complete terrigenous record of the Himalayan flux over the last 1–2 m.y.

This expedition builds on knowledge acquired during earlier drilling and seismic explorations of the Bengal Fan (Deep Sea Drilling Project [DSDP] Leg 22, Ocean Drilling Program [ODP] Leg 116, and R/V Sonne Cruises SO93, SO125 and SO188) and on current studies of the tectonic, geologic, geomorphological, and sedimentological processes acting on the Himalaya, the floodplain and delta of the Ganga-Brahmaputra, and the Bengal Fan. This expedition is one part of an integrated effort for drilling syntectonic basins around the Himalaya to improve our knowledge of monsoon evolution and its interaction with Himalayan growth and erosion.