Erosional History of the Himalayan Range Since the Last 180 kyr: Clay Mineralogical and Geochemical Investigations From the Bay of Bengal

Abstract:

Himalayan range and Indo-Gangetic plain are drained by one of the world’s largest river system of the world: the Ganges-Brahmaputra Rivers. This river system is the first in term of sediment transport and thus constitute an interesting region to establish a relation between erosion and climate. Sediments from the Bay of Bengal indicate that the strength of summer monsoon rainfall is an important factor driving weathering and erosion of the Himalaya.

Results of a high-resolution clay mineralogy study combined with major elements geochemistry and oxygen isotopes stratigraphy are reported for a deep-sea piston core collected 300 km off the Ganges-Brahmaputra Rivers estuary in the northern part of the Bay in Bengal. In this study, the top part (first 13.5 m) of Core MD12-3412 covers the last climatic cycle (last 180 kyr). This core reveals a monsoon-controlled chemical weathering and physical erosion history during the last 180 kyr in the Himalayan range and the Ganges-Brahmaputra Basin.

Data show the contribution of Ganges-Brahmaputra Rivers, which drain the Himalayan range and the Indo-Gangetic plain. Clay mineral assemblages are dominated by illite and smectite, with lesser abundance of chlorite and kaolinite. Smectite/(illite + chlorite) and illite chemistry index are used as indices of chemical weathering rates. Thirty five new samples for εNd(0) analyses were selected (in turbidite and hemipelagic layers) during glacial and interglacial periods.

 Himalayan range is characterized by εNd(0) ≈ -16, whereas εNd(0) values along the Arakan coast are around -8. In this work we compared with εNd(0) values obtained previously on the free-carbonated fraction on Core MD77-180 which show that sediment from the eastern Bay of Bengal results from the mixing of material from the Himalayan and Indo–Burman ranges (with an average value of εNd(0) ≈ -13 for the last climatic cycle). These analyses give us information about the material coming from Ganges-Brahmaputra Rivers system and Indo-Burman ranges and, in turn, on the Indian summer monsoon intensity.