Extraction of effective sedimentary signals from rivers in Bangladesh and their application in the Bay of Bengal

Abstract

River sediments compositions in Bangladesh were measured to extract effective signals of chemical weathering, sedimentary processes and provenances and applied to sedimentary record in the Bay of Bengal (BoB). Weathering indexes including the chemical index of alteration (CIA), weathering index of Parker (WIP), αAlE and related diagrams indicated overall weak to intermediate chemical weathering intensity in modern Ganges-Brahmaputra-Meghna (G-B-M) catchment. Sedimentary processes controlled sediment mineralogical and chemical composition to a certain extent, as reflected in the distinctions between suspended loads and bedloads. The suspended loads were richer in phyllosilicates than the bedloads in the Brahmaputra and the Meghna River sediments, and the Meghna River bedload exhibited sedimentary recycling and quartz dilution features. The Ganges River sediments showed multiple recycling and source mixing features. Extracted provenance proxies indicated that the Brahmaputra River sediments got relatively more effects from Himalayan mafic to intermediate rocks, while the Ganges River sediments indicate a mixture from the Himalaya and Indian Peninsula. more effects from ultramafic rocks were revealed for the Meghna River sediments. By comparing the extracted provenance proxies of different rivers and applying them to the identification of sediment sources in the Bay of Bengal (BoB), the Brahmaputra River is suggested to have been the primary supplier of sediments to the central-northern BoB since the last glacial period as a result of the highest erosion rate in the eastern syntaxis, which provides a new understanding of the sediment “source-sink” process in the BoB and indicates that effective extraction of fluvial information is crucial for marine sedimentology studies.