5:15 PM - 6:45 PM
[MIS12-P28] Reconstruction of paleoenvironmental changes by biomarker analysis of deep-sea drilling cores from the Bay of Bengal during the Pliocene to Pleistocene
Keywords:Mangrove, Turbidite, IODP, Alkenone, Long chain alkyl-diols, Terpenoids
The Bengal Fan in northeastern Indian Ocean is a submarine fan formed by transport of huge clastic sediments by the confluent Ganges and Brahmaputra rivers as a direct result of the India–Asia collision and uplift of the Himalayas and the Tibetan Plateau (Curray et al., 2002). Turbidite in submarine fan is basically formed by turbidity currents caused by flood and earthquake, and terrigenous organic matter (OM) by delivering from land area through the turbidity current is abundant. Thus, the sedimentary OM analysis can be applied to evaluating transport and depositional processes in the turbiditic sediments. In the present study, we analyzed biomarkers in sediment core samples from the Bengal Fan to reconstruct depositional environments of turbiditic sequences and the variations in marine paleoenvironments and paleovegetation of hinterland from the Pliocene to Pleistocene.
We used the sediment cores recovered at the Bengal Fan, Site U1444, by Integrated Ocean Drilling Program (IODP) Expedition 353. Freeze-dried sediments were extracted by solvents and then separated into fractions by silica-gel column. These fractions were analyzed by GC-MS and GC-FID.
We identified algal biomarkers such as long-chain alkenones, long-chain alkyl diols, and steroids, as well as terrestrial plant-derived biomarkers such as long-chain alkanes and terpenoids. In the turbidite sediments, we evaluated sedimentary processes by analysis of algal and mangrove-derived biomarkers. In particular, the world’s largest mangrove forest is known to distribute in the Ganges Delta, and the mangrove-derived OM was likely to be delivered with clastic sediments to the Bengal Fan. Thus, our results that the abundant detection of the mangrove-derived biomarker is concordant with the depositional setting and vegetation of hinterland. In the hemipelagic sediments, we reconstructed sea surface and subsurface paleotemperatures based on long-chain alkenones (UK’37) and alkyl diols (LDI), although it is only low-resolution analysis. These temperature records indicate gradually decrease with global cooling during the Pliocene to Pleistocene. The paleoclimatic trends recorded by terrestrial plant biomarkers including mangrove-derived one is different from those of marine algal biomarkers, indicating the differences of climatic responses between terrestrial plants and marine algae.
We used the sediment cores recovered at the Bengal Fan, Site U1444, by Integrated Ocean Drilling Program (IODP) Expedition 353. Freeze-dried sediments were extracted by solvents and then separated into fractions by silica-gel column. These fractions were analyzed by GC-MS and GC-FID.
We identified algal biomarkers such as long-chain alkenones, long-chain alkyl diols, and steroids, as well as terrestrial plant-derived biomarkers such as long-chain alkanes and terpenoids. In the turbidite sediments, we evaluated sedimentary processes by analysis of algal and mangrove-derived biomarkers. In particular, the world’s largest mangrove forest is known to distribute in the Ganges Delta, and the mangrove-derived OM was likely to be delivered with clastic sediments to the Bengal Fan. Thus, our results that the abundant detection of the mangrove-derived biomarker is concordant with the depositional setting and vegetation of hinterland. In the hemipelagic sediments, we reconstructed sea surface and subsurface paleotemperatures based on long-chain alkenones (UK’37) and alkyl diols (LDI), although it is only low-resolution analysis. These temperature records indicate gradually decrease with global cooling during the Pliocene to Pleistocene. The paleoclimatic trends recorded by terrestrial plant biomarkers including mangrove-derived one is different from those of marine algal biomarkers, indicating the differences of climatic responses between terrestrial plants and marine algae.