Sources of organic carbon and depositional environment in the Bengal delta plain sediments during the Holocene period |
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Authors: | Hossain M Anawar Takahito Yoshioka Eiichi Konohira Junji Akai M C Freitas Shafi M Tareq |
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Institution: | 1. Instituto Tecnológico e Nuclear Reactor, Apartado 21, E.N. 10, 2686-953, Sacavém, Portugal 2. Field Science Education and Research Center, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, 606-8502, Japan 3. Graduate School of Environmental Studies, Nagoya University, Chikusa-ku, Nagoya, 464-8601, Japan 4. Department of Geology, Niigata University, Ikarashi 2-no-cho, Niigata, 950-2181, Japan 5. Department of Environmental Sciences, Jahangirnagar University, Dhaka, 1342, Bangladesh
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Abstract: | This study investigated the sources of organic matter and sediment depositional environment within fluviatile sediments of
the Ganges–Meghna (GM) delta plains. The very low contents of trace metals e.g., chromium (Cr), cobalt (Co), scandium (Sc),
and vanadium (V), organic carbon content, and cerium (Ce)-anomaly data of sediments indicate the redox conditions that fall
within the boundary of oxic–anoxic condition, with dominantly oxic conditions in the sediment deposition environment. The
higher atomic carbon nitrogen (C/N)a ratios and depleted stable carbon isotope ratio (δ13C) values for sediments from three study areas indicated the terrestrial sources of organic matter derived from C3 plant materials, whereas the contribution of organic materials from C4 vegetation and riverine productivity is low. Some silty sand samples exhibited lower (C/N)a ratios and enriched δ13C values in Sonargaon and Faridpur areas that are attributed to the adsorption of ammonium ions on clay minerals and the contribution
of organic matter from C4 plants. Total sulfur over total organic carbon (TS/TOC) ratios in sediments of the Ganges delta reflect the nonmarine environments
of sediment deposition. The lower ratios of syringyl to vanillyl phenols (S/V), cinnamyl to vanillyl phenols (C/V), and acid
to aldehyde in vanillyl phenols (Ad/Al)v observed in Daudkandi indicate that the lignin in sediments derived from dominant
woody gymnosperm sources and is very highly degraded. By contrast, the S/V ratio, C/V ratios, and Ad/Al]v ratios in Faridpur
suggest that the lignin in sediments derived from a mixture of woody and nonwoody angiosperm plant tissue contribution that
underwent high degradation as well. |
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