Abstract
A 39 m long sediment core (MD161-19) spanning 320 ka, collected from the intermediate water depths of (1480 m) of Mahanadi offshore was subjected to provenance analyses using Sr and Nd isotope systematics. The Sr–Nd isotope ratios of MD161-19 fall on the mixing line defined by Ganga and Brahmaputra main stem averages. Strontium and Nd isotope ratios along with Fe/Al ratio clearly show the predominance of Himalayan sediments in the study area. The significant temporal variations in the Sr–Nd isotope ratios observed for the entire depositional age (320 ka) may be attributed to changes in the relative sediment contribution by Ganga and Brahmaputra river systems draining terrains with contrasting Sr–Nd isotope ratios. The temporal geochemical profiles coupled with precipitation profile show that wet-phases during stadials led to enhanced erosion of the trans-Himalayan batholiths (THB) rocks (characterized by high εNd values) possibly due to glacial expansion in the higher reaches of the Brahmaputra catchment. The warm interstadials coupled with enhanced precipitation are accompanied by a shift towards lower εNd values which may be attributed to extensive erosion of the Ganga catchment area comprising rocks characterized by lower εNd values and diminished THB contribution due to lack of glacial influence.
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