SOME ASPECTS ON THE VARIATIONS IN DEPOSITIONAL FLUX OF EXCESS THORIU-230 IN THE CENTRAL INDIAN BASIN DURING LATE QUATERNARY

Examined in this paper is the tentative history of the depositional fl ux of Th-230xs (the unsupported fraction of Th-230 scavenged from the overlying water column), for the Late Quaternary period from a sedimen t core of the Central Indian Basin (CIB). The measured depositional fl ux of Th-230-xs is found substantially higher than that of the possibl e theoretical flux from the overlying water column. Historical records , reconstructed from the Th-230-xs chronology suggests that the deposi tional flux has varied considerably with time, reflecting an enhanced scavenging during the Holocene and the preceding interglacial periods whereas, comparatively lower flux than the predicted one occurred duri ng the Last Glacial Maximum (LGM) period. The average ratio of the mea sured depositional flux to that of the predicted flux from the overlyi ng water column, indicates that the core site acts as a sink for Th-23 0-xs and based on the existence of bottom current activity; the Th-230 -xs could be the result of focusing of younger sediments. The depositi onal index (Di) has also been calculated to quantify the extent of lat eral supply throughout the core with time. The estimated (Di) suggests that bottom focusing and feeble deposition and/or winnowing processes had occurred and that the former was most prevalent during the Holoce ne and the preceding interglacials, whereas the latter was observed at the LGM period.