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. (4th September 2019) - Cai, Mingjiang
Abstract: Systematic variation in elemental and Sr‐Nd isotopic compositions of the clay‐sized (<2 μm) 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 87 Sr/ 86 Sr, and low εNd 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 87 Sr/ 86 Sr and chemical index of alteration values, and high εNd 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. Plain Language Summary: The Indian summer monsoon is an extremely important part of the Earth's climate system. Weathering and erosion of sediments are deeply affected by monsoon rainfall. Since 3.8 Ma, the geochemical records suggest that the clay‐sized siliciclastic fractions at Site U1456 were mainly derived from the Indus River when the Indian summer monsoon was generally weak. In contrast, the siliciclastic sediment supply from the Deccan Traps increased when the monsoon intensified. In particular, we propose that chemical weathering intensities can be tracked using K/Al ratios and chemical index alteration and the smectite/(illite + chlorite) in the fine fraction of marine sediments from the eastern Arabian Sea since 3.8 Ma. Conducting research in the region is of great importance for understanding past and present climatic conditions. Key Points: The silicate weathering intensity in the western Himalayan flood plains has primarily been controlled by the monsoon climate since 3.8 Ma The Indus River and Deccan Traps are the two dominant provenances for clay‐sized sediments in the eastern Arabian Sea Summer monsoon intensity has dominated the input from the Indus River and Deccan Traps to the eastern Arabian Sea