Clay-mineral accumulation rates in the Arabian Sea during the late Quaternary

Abstract

The regional variations in clay-mineral concentrations in 39 turbidite-free and undisturbed deep-sea sediment cores from the Arabian Sea are compared with distribution patterns of clay-mineral accumulation rates during the Holocene and the last glaciation. Dust plumes from the Red Sea area, Arabia, Mesopotamia, Iran and Pakistan can be traced by accumulation rates of mineral-specific dust loads. During the late Quaternary, the major proportions of aeolo-marine sediments in the western Arabian Sea were derived from Arabia during the summer season. The clay-mineral assemblage in these dust plumes consists of illite, smectite, kaolinite, chlorite and palygorskite, in decreasing order of abundance. The distribution pattern of palygorskite in particular reveals that dust transport from southern Arabia occurs mainly with northwesterly to westerly winds in the mid-troposphere. Dust plumes from Iran and Pakistan, which are characterized by high chlorite content, are dispersed by northwesterly winds over the northwestern Arabian Sea. Dust contributions from the Red Sea area, which are rich in smectite and characterized by the occurrence of amphiboles, are transported to the Gulf of Aden. The amount of dust related to northeast monsoon winds during the winter season appears to be negligible when compared to the proportions borne on other dust-bearing winds. In addition to aeolian contributions we distinguish two fluvial contributions: a chlorite-, illite-, kaolinite- and quartz-rich assemblage from Oman and Pakistan into the Gulf of Oman, and a smectite-rich assemblage which is dominant off southern India, originating from rivers that drain the Indian subcontinent. The significant difference between the Holocene and glacial accumulation rates of wind-transported clay minerals consist in the higher abundance of quartz, illite and chlorite in the northwestern Arabian Sea during the last glaciation. This pattern indicates intensified dust contributions by northwesterly winds from the Persian Gulf area, which was dry during glacial times.