Geochemistry of sediments of the eastern continental shelf of India

A. Mascarenhas, A.L. Paropkari, P.S.N. Murty

Abstract



The bulk and partition geochemistry of Al, Fe, Ti, Mn, Zn, and Cu have been investigated in sediments of the eastern continental shelf of India. The results show that (1) the bulk geochemistry varies from one shelf unit to the other, (2) all the elements studied have both lithogenous and non-lithogenous components in the sediments, and (3) the percentage contributions made by the lithogenous component to the concentrations in the bulk samples are highest in respect of Al and Ti, followed next in order by Fe, lowest in respect of Mn, while the values for other elements lie in between the percentage contributions for Al and Ti on the one hand and Mn on the other hand. The variations in the bulk geochemistry of the sediments have been explained in terms of the variations in the percentage contributions made by the lithogenous and non-lithogenous components to the concentrations of the elements in the bulk samples, textural variations and dilution by the calcium carbonate phase of the sediments. In the non-lithogenous fraction, Fe hydroxide and Mn hydroxide appear to be the dominating constituents contributing to the concentrations of these elements in this fraction and other elements, through their ability to absorb trace metals from the waters. The inter-relationships obtained among the various elements support this conclusion. Similarity in the metal/Al ratios computed for the elements in the continental shelf region with those computed for the fluvial sediments from the adjacent river systems, suggest that colloids of Fe and Mn hydroxides could have been formed in the river systems, transported through the estuaries along with their trace metal content without any modification and deposited in the shelf region

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