Depositional history and Indian summer monsoon controls on the silicate weathering of sediment transported to the eastern Arabian Sea: Geochemical records from IODP Site U1456 since 3.8 Ma

Systematic variation in elemental and Sr-Nd isotopic compositions of the clay-sized (<2 mu m) siliciclastic fraction from the International Ocean Discovery Program (IODP) Site U1456 (Laxmi Basin) provides valuable insights into dynamic changes in continental weathering intensity in the western Himalayas and sediment inputs from the Indus River and Deccan Traps to the eastern Arabian Sea. Long-term, high-resolution proxy records from the sediment core reveal that the main sources (i.e., Indus River and Deccan Trap basalts) of the fine-grained detrital sediments have significantly changed with Indian summer monsoon variation over the studied time interval. During two depositional periods (3.8-3.3 and 2.7-1.2 Ma) corresponding to a weak Indian summer monsoon, the Indus River contributed fine-grained sediments with high K/Al, high Sr-87/Sr-86, and low epsilon Nd to the study site. Between 3.3 and 2.7 Ma and between 1.2 and 0 Ma, deposition in the eastern Arabian Sea was governed by large inputs of Deccan Trap-derived basaltic sediments, characterized by high Mg/Al and Fe/Al, low Sr-87/Sr-86 and chemical index of alteration values, and high epsilon Nd values, associated with a change to a stronger Indian summer monsoon driving stronger chemical weathering. Synchronous changes in the geochemical proxies since 3.8 Ma highlight that variations in the inputs of siliciclastic sediments and Indian summer monsoon development are closely coupled.