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M. V. Shankaranarayana Guptha ¹

Affiliations
1 Natiopal Institute of Oceanography, Dona Paula, Goa - 403004, IN

Abstract

The degree of fragmentation and colour of the skeletal fragments, colouration in benthic foraminifers have been studied in surficial sediment samples collected from forty stations from the continental shelf region between Ratnagiri in the south and Indus canyon in the north. The abundance peaks of fragmented shells correspond to the terrace depths of -65, -75, -85 and -92 m in the outer shelf region off Ratnagiri which indicate the different phases of eustatic sea levels. It is inferred from the occurrence of abundance peaks at similar depths in the other regions of the continental shelf that they must correspond to the presence of lowered strands. The disposition of the black shells in a linear fashion parallel to the coast line at the depths mentioned above also supports the proposition.

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R. R. Nair ¹, N. H. Hashimi ¹, M. V. Shankaranarayana Guptha ¹

Affiliations
1 National Institute of Oceanography, Dona Paula, Goa-403004, IN

Abstract

Dredging on the western continental shelf of India has shown that the most common rock types outcropping on the irregular topography of the outer shelf (70-90 m) are algal limestones and shelly limestones containing superficial ooids and pelletoids, while those on the upper continental slope (130-180 m) are algal bryozoan limestones. The limestones have a radiocarbon age ranging between 9,000 and 11,000 years. Depositional environment on the continental shelf during the Holocene appears to be characterised by shallow waters in association with lagoon-barrier beach environment.

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M. V. Shankaranarayana Guptha ¹

Affiliations
1 National Institute of Oceanography, Dona Paula, Goa 403004, IN

Abstract

Authigenic gypsum has been encountered in a deep sea core RC9-157 from the southeastern Arabian Sea at a depth of 4111 m which is a zone of lysocline. The formation of gypsum in the deep sea region is attributed to the prevailing sulphate rich equatorial waters which were constantly fed by calcium through the dissolution of calcareous tests. Another plausible mechanism that may be proposed is that of the sulphate rich Antarctic bottom water which is playing a vital role in bringing about the crystallisation of gypsum by utilising the calcium available through dissolution.

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M. V. Shankaranarayana Guptha ¹

Affiliations
1 National Institute of Oceanography, Dona Paula, Goa 403004, IN

Abstract

A deep sea core RC9-156 collected in the Arabian Sea at a water depth of 4583m was analysed for calcareous nannoplankton and dissolution studies. Twelve species of nannoplankton were identified and based on the assemblage, it is suggested that the age of the sediment is late Quaternary. The alternate fossiliferous and un-fossiliferous bands encountered in the core is attributed to the fluctuations in the rate of sedimentation by the river Indus during glacial and interglacial periods.

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M. V. Shankaranarayana Guptha ¹

Affiliations
1 National Institute of Oceanography, Dona Paula (Goa) 403004, IN

Abstract

Fifty-four snapper samples from the northwestern continental shelf of India have yielded fifteen species of calcareous nannoplankton along with a few reworked ones. Among the species encountered, Gephyrocapsa oceanica was most predominant, being distributed in all the stations. The patchy and sparse distribution of nannoplankton suggests that the flora has undergone intense grazing. Low diversity of nannoplankton indicates a marginal environment.

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