SR ISOTOPES AS AN INDICATOR OF GANGES-BRAHMAPUTRA PROVENANCE CHANGES DRIVEN BY SHIFTING SOUTH ASIAN MONSOONS

Sediments carried by the Ganges-Brahmaputra river system and deposited in the Bengal delta have their main sources in rock outcrops of the Himalayas and Tibetan Plateau. The major rock units of this region each have characteristic Sr-isotope signatures, which can be used to determine the dominant source areas for sediments deposited in the delta. This makes Sr-isotopes a useful tool for determining temporal changes in erosion patterns and sediment provenance for the Ganges and Brahmaputra rivers. During the Late Quaternary, the strength and distribution of the southwest monsoon has varied with regional insolation, resulting in a major precipitation peak in the early Holocene. Downcore variations in Sr-isotope ratios suggest that delta response to such millennial-scale climate changes can be resolved from the stratigraphic record. In this study, ⁸⁷Sr/⁸⁶Sr has been measured on borehole samples from Holocene deposits of the Ganges-Brahmaputra delta to determine the effects of shifting monsoon patterns on this sediment dispersal system. These data provide valuable information regarding the short-term response of Himalayan erosion to the changing South Asian monsoon climate.