Texture and mineralogy of sediments from the Ganges-Brahmaputra-Meghna river system in the Bengal Basin, Bangladesh and their environmental implications |
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| Authors: | D K Datta V Subramanian |
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| Institution: | (1) School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110 067, India, IN |
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| Abstract: | The Bengal basin, Bangladesh, represents one of the most densely populated recent floodplains of the world. The sediment
flux through the basin is one of the highest on a global scale. A significant portion of this sediment load find its sink
in the basin itself because of its lower elevation and frequent flooding. The textural, mineralogical and chemical nature
of the sediments thus have an important bearing on the environmental quality of the basin as well as for the Bay of Bengal.
The sediment load of the Ganges-Brahmaputra-Meghna (GBM) river system consists exclusively of fine sand, silt and clay at
their lower reaches within the Bengal basin, Bangladesh, and is deposited under uniformly fluctuating, unidirectional energy
conditions. The sediments have a close simitarity in grain size with the sediments of the surrounding floodplain. The mineral
assemblage is dominated by quartz and feldspars. Illite and kaolinite are the major clay minerals, and occur in almost equal
proportion in bed sediments. The heavy mineral assemblage is dominated by unstable minerals which are mostly derived from
high-rank metamorphic rocks. The characteristic smaller grain-size, i.e. having large surface-to-mass ratios, and the mineralogy
of sediments suggests that they are susceptible to large chemical adsorptive reactions and thus could serve as a potential
trap for contaminants. However, the sediments of the GBM river system in the Bengal basin, Bangladesh, shows lower concentration
of Pb, Hg and As, and a marginally higher value for Cd as compared to that of standard shale. Considering population density
and extensive agricultural practice in the basin, the sediments can in the long run become contaminated.
Received: 9 November 1994 · Accepted: 18 June 1996 |
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| Keywords: | Grain size distribution Mineralogy Bengal basin Bangladesh |
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