Evidence for provenance change in deep sea sediments of the Bengal Fan: A 7 million year record from IODP U1444A

摘要

Previously published geochemical and mineralogical data have revealed conflicting views on the provenance of the deep-sea sediments in the Bengal Fan. Here we report results of a study for a 330-m sequence consisting of both turbitide and semi-pelagic sediments recovered at the Site U1444A during the IODP 353 Expedition. A novel technique using the optically and thermally stimulated luminescence (OSL and TL) signatures from quartz and K-feldspar has been employed to characterise the mineral compositions of the sediments. We show that the quartz luminescence sensitivity clearly differentiates the four sedimentary units. There is a distinct increase of quartz luminescence sensitivity in Unit 2 during the time interval of similar to 3.5-0.5 Ma. Analyses of the luminescence signal components in quartz and the ratio of the K-feldspar and quartz also point to a change in Unit 2 relative to the other three units. We interpret such changes in the mineralogical compositions through the sequence as reflecting a change in the provenance over the last 7 million years in the western Bengal Fan. We attribute the quartz with enhanced luminescence sensitivity in Unit 2 to the contribution from the sources associated with Indian rivers. We infer that the delivery of the sediments from Indian peninsula to IODP Site U1444A is facilitated by a weakening in the turbidite deposition which is dominated by weathering products from the Himalayas. We speculate that the relatively high elevation of the 85 degrees E Ridge may act against the flow through and the associated deposition of turbidity current originated from the Himalayas.