Provenance Of Detrital Sediment Fraction In The East Arabian Sea As Well As The Response To The South Asian Moonsoon Since Pliocene

Clay mineralogy and siliciclastic grain-size of the detrital fraction of sediments from IODP Site U1456 (Laxmi basin) have been analyzed to establish past evolutions of monsoon intenisty and sediment inputs to the eastern Arabian Sea since 5.3 Ma.The results show that the main components of clay minerals in the terrigenous sediments of site U1456 are composed of illite,smectite,chlorite and kaolinite. The main components are smectite (0?90%, the average content of smectite ?44%) and illite (the average content of illite ?44%),the secondary components are chlorite(1?26%,the average content of chlorite?7%) and kaolinitc (0?19%,the average content of kaolinite ?5%)Based on the variations of the smectite, illite, kaolinite and chlorite in clay minerals compositions since 5.3 Ma, the site U1456 could be divided into four distinct depositional units. Zone 1 (early to middle Pliocene; 5.3-3.2 Ma, illite contents mostly display higher values -60%), Zone 2(middle Pliocene; 3.2-1.7 Ma, smectite contents mostly display higher values ?56%), Zone 3 (late Pliocene to middle Pleistocene;1.7-1.2 Ma, illite contents mostly display higher values ?63%), Zone 4 (middle Pleistocene to Holocene; 1.2-0 Ma, smectite contents mostly display higher values?59%).Clay mineral distribution show that the sediment in IODP Site U1456 are mainly from the Indus River from 5.3 to 3.2 Ma and from 1.7 to 1.2 Ma. A significant increasing of sediment supply from Deccan Trap have been observed from 3.2 to 1.7 Ma and since 1.2 Ma ago. The increase of Indian summer monsoon intensity is associated with a decrease of smectite / (illite + chlorite) ratio and vice versa.The shift of the IODP U1456 sediment sources around 3.2 Ma, 1.7 Ma, 1.2 Ma could be associated to the change of the Indian summer monsoon intensity. The detrital sediments in the east Arabian Sea were mainly derived from the Indus River when the South Asian monsoon was persistently weaker; however, Sediment from Deccan Traps increased significantly when the Indian summer monsoon intensified.The sharply increase of mass accumulation rate in 1.7-1.2 Ma could be corresponding with a reorganization of Indus tributary (one tributary shifted from Ganges River to Indus River) and/or enhanced physical erosion rate of the Himalayas.