Effects of climate and sea level change on sedimentation in the eastern Bengal Fan during the late Quaternary

Abstract

The Bengal Fan is a vast repository of clastic sediments from the Himalayas, Peninsular India and Indo-Burman ranges. Many ancient submarine channels through which the turbidity currents operated in the Bay of Bengal are currently inactive. These defunct channels provide some of the best sediment records of continental weathering and climate. Here, we present the results of a sedimentological, geochemical, and Sr-Nd isotopic study done on a well-dated sediment core (27–1.5 kyrs BP) collected from the now-defunct submarine channel in the eastern Bay of Bengal to examine the roles of various environmental factors on the growth of the fan. Results of our study suggest that active fan progradation at the eastern margin of the Bengal basin continued until ∼12 kyrs BP, with rapid deposition of coarse-grained terrigenous flux. Deposition of sediments from Indo-Burman-Arakan (IBA) ranges and Ganga-Brahmaputra rivers through channel E7 was active during 27 to 12 kyrs. Subsequently, hemipelagic sedimentation from the Irrawaddy increased. Unlike other major fans, the Bengal Fan had a very active coarse-grained terrigenous flux during the Last Glacial Maximum and subsequent deglacial period. The post-12 kyr BP cessation of coarse-grained terrigenous deposition despite significant sediment influx from the Himalaya/Indo-Burman-Arakan Ranges was likely a result of the inland retreat of river mouths due to sea level rise and the subsequent detachment of the submarine channels from the coast. Our study also suggests that the sedimentation in the Bengal Fan is less sensitive to the variations in the rainfall associated with the Indian Summer Monsoon than the sea level changes. These findings underscore the complex interplay between the climate and coastal geomorphology in shaping the Bengal Fan.