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Ch M. Rao ¹, A. L. Paropkari ¹, A. Mascarenhas ¹, P. S. N. Murty ¹

Affiliations
1 National Institute of Oceanography, Dona Paula, Goa 40300, IN

Abstract

Phosphate content in the bulk sediments range from 0.02 to 2.17% and on carbonate free basis it varies from 0.03 to 6.57%. The partition studies indicate that contribution from the acid resistant detrital minerals (HCl insolubles) is negligible. In the inner shelf, the phosphorus is mainly associated with iron (as ferric-phosphate?) and organic carbon. In the outer shelf/slope its association with carbonate suggests its authigenic/diagenetic origin. This is also supported by X-ray diffraction studies wherein the apatite peak is revealed in some samples. In general, sympathetic relationship of phosphorus with organic carbon in the study region indicates genetic relationship between these two elements, which is an important condition for phosphatogenesis. Further, these studies suggest that the outershelf/slope region between Bombay and Quilon is the promising area for detailed exploration for phosphorite deposits.

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V. Purnachandra Rao ¹, Ch. M. Rao ¹, A. Mascarenhas ¹, K. Mohan Rao ², N. P. C. Reddy ², H. C. Das ³

Affiliations
1 National Institute of Oceanography, Dona Paula 403 004, Goa, IN
2 National Institute of Oceanography, Regional Centre, 52, Kirlampudi, Layout, Visakhapatnam 530 023, IN
3 Oil India Limited, Duliajan, Assam 786 602, IN

Abstract

Sedimentological and geochemical investigations of the sediments in a core from the eastern continental margin of India, at a water depth of 1200m, revealed two distinct sediment types. The Late Pleistocene sediments are greyish-black in colour and consist of mud turbidites in the lower part and dolostone breccia in the upper part. They also consist of illite and chlorite-rich clay minerals with high organic carbon and sulfur. Organic matter is of dispersed nature. These are similar to black shales and are apparently formed by rapid burial of terrigenous organic matter by turbidites with intermittent reducing conditions during lowered sealeveIs. Dolostone fragments appear to have been transported by mass movement processes during the terminal pleistocene. The Holocene sediments: are moderate yellowish-brown in colour and with detrital vivianite nodules at the base. These sediments are clayey with mont-morillonite-rich, illite-poor clay minerals, lower organic carbon and sulfur contents and ferruginised pyrite grains, deposited under oxidising conditions. The marked changes in the sedimentary environments are attributed to climate and sealevel changes during Pleistocene and Holocene.

Keywords

Environment, Pleistocene, Holocene, Black Shales, Off Penner River, Continental Margin.

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