LATE PLEISTOCENE SEDIMENTATION - A CASE-STUDY OF THE CENTRAL INDIAN-OCEAN BASIN

Concentration-depth profiles of excess Th-230 have been measured in fi ve sediment cores from the central Indian Ocean Basin to determine the ir accumulation rates and excess Th-230 flux to the depositional envir onment. Sedimentation accumulation rates ranged between 1 and 5 mm ky- 1. The excess Th-230 inventories in the cores range from 44 to 481 dpm cm-2, considerably lower than that expected from its production in th e overlying water column. These low excess Th-230 inventories (relativ e to its production) have been attributed to the effects of winnowing by bottom currents. The absence of Th-230ex in core (SK-176) has been attributed to the lack of sediment deposition in this area caused by t he influence of Antarctic Bottom Water (AABW). This study shows that t he deposition of biogenic silica and lithogenic components exhibited o rders of magnitude variations during Late Pleistocene. The biogenic fl ux variation are attributed to productivity changes while the episodic variations in the non-biogenic flux could result from major changes i n the influx of terrigenous materials via the Ganges-Brahmaputra.