Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Rajiv Nigam ¹, M. G. Anantha Padmanabha Setty ¹, N. V. Ambre ¹

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

Abstract

Sixty-Four benthonic foraminiferids are reported from Dabhol-Vengurla innershore neritic environmentand they are listed in orderof their relative abundance. Small microenvironments or milieus createdby the dominance of Trochammina inflata and Ammobaculites agglutinens on the one handand the miliolid fauna on yhe other are noted.

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Rajiv Nigam ¹, J. S. Sarupria ¹

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

Abstract

Q-mode cluster analysis explains the spatial distribution data of living benthonic foraminiferids from the inner shelf off Ratnagiri. Two main biotopes and two subbiotopes are recognised within the study area; biotope A, characterised by Trochammina inflata (Montagu), covers the inner shelf north of Ratnagiri and demarcates the influence of fresh-water from Shastri and Vashishti rivers. Biotope B characterised by Nonion and Ammonia covers the inner shelf south of Ratnagiri and represents less influence of fresh water from Rajapur and Vaghotan rivers. Two sub-biotopes in Bare represented by the additional occurrence of Ammobaculites agglutinans and Nonionella respectively. Relatively low and high rate of sedimentations were noted in areas of biotopes A and B respectively.

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Rajiv Nigam ¹

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

Abstract

One hundred and two taxa of benthic foraminifera are reported from the neritic environment (15-60 m) of Vengurla-Bhatkal area. Q-mode factor analysis reveals 6 important foraminiferal assemblages accounting for 92% of the information given in original data matrix. The assemblages are - Nonion - Bulimina Ammobaculites, Bolivina, Bulimina - Nonionella - Ammobaculites Nonionella - Bulimina and Ammonia. Based on the ecology of the fauna it is concluded that a general hyposalinal environment prevails in the study area. Geographical distribution of well-known hyposalinaI species/assemblage can be used to study the spread of brackish water along the coastal area.

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S. N. Bhalla ¹, Rajiv Nigam ²

Affiliations
1 Department of Geology, Aligarh Muslim University, Aligarh, IN
2 National Institute of Oceanography, Dona Paula, Goa, IN

Abstract

Q-mode cluster analysis of thirty species of foraminifera from six sandy beaches of India reveals that the East and West coasts belong to two different faunal realms. Some possible ecological factors responsible for differences in fauna are summarised.

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Rajiv Nigam ¹, Neloy Khare ¹

Affiliations
1 Geological Oceanography Division, National Institute of Oceanography, Dona Paula, Goa 403 004, IN

Abstract

Twenty one surface sediment samples collected from the inner shelf region off Karwar at 22-52 m water depth range have been studied for foraminiferal content. Based on the external test morphology the entire foraminiferal population (148 species) can be placed into two broad morpho-groups namely angular-asymmetrical and rounded-symmetrical morpho-groups. The surficial distribution of these groups revealed that angular-asymmetrical morpho-group gets adversely affected by high turbulence associated with increased fresh water river disCharge, whereas, rounded-symmetrical morpho-group responded in a reverse manner. Since areal extent of river induced turbulence depends upon fresh water discharge due to monsoonal rains, the results show high potential in generating proxy data for the reconstruction of paleomonsoonal history through the study of morpho-groups in sub surface sediments of coastal regions.

Keywords

Foraminifera, Morphology, Palaeoclimate, West Coast, Arabian Sea.

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Rajiv Nigam ¹, Afimjit Mazumder ¹, Pravin J. Henriques ², Rajeev Saraswat ¹

Affiliations
1 Geological Oceanography Division, National Institute of Oceanography, Dona Paula - 403 004, IN
2 Geology Department, St. Xaviers College, Mumbai- 400 001, IN

Abstract

In order to study the response of benthic foraminifera, especially the rectilinear bi- and Tri-Serial benthic foraminifera (RBF) to oxygen-Depleted conditions from the Arabian Sea off central west coast of India, 103 surface sediment samples collected from a water depth of 15m to 3300m were studied for the benthic foramini feral content. A total of 383 recent benthic foraminiferal species were identified. Out of the total 383 benthic foraminiferal species identified in the study area, 65 species belong to 18 rectilinear bi- and tri-serial benthic foraminifer genera. The RBF abundance remains consistently high (>40%) between 90 m to ∼1200 m water depth. The intermediate depth zone of increased abundance of RBFs coincides with the prominent intermediate water oxygen minimum zone of the Arabian Sea (upper boundary ∼100 m and lower boundary ∼1000 to 1250 m). The other significant abundance (>40%) of rectilinear benthic foraminiferal forms is reported from the water depth range &#∼60 m with the maximum abundance reaching ˜78% at the water depth of 56 m. This zone has also been reported to be affected by seasonal severe Oxygen-Depleted conditions. Therefore, we propose that the increased abundance of RBF may be used as an indicator of Oxygen-Depleted conditions in the Arabian Sea. This benthic foraminiferal response to oxygen-depleted conditions, especially from the shallow water depths is significant as it can be applied to document the geologic extent of shallow water Oxygen-Depleted conditions that have been suggested as a consequence of spurt in the anthropogenic activities in the coastal regions.

Keywords

Oxygen Minima Zone, Rectilinear Benthic Foraminifera, Deep And Shallow Water OMZ, Central West Coast Of India.

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Rajiv Nigam ¹, Rajeev Saraswat ¹, Sujata R. Kurtarkar ¹

Affiliations
1 Micropaleontology Laboratory, Geological Oceanography Division, National lnstitute of Oceanography, Dona Paula - 403 004, Goa, IN

Abstract

Culture experiment has been carried out to observe the response of Pararotalia nipponica (Asano) to different salinities and its salinity tolerance limits. The specimens of P nipponica kept in 33%0 saline water achieved optimum growth, while rest of the specimens maintained under either higher or lower salinities showed comparatively lower growth Pararotalia nipponica specimens kept at 10%0 and 15% salinity started becoming opaque and later their test dissolved, within a span of 25 days. Towards the end of experiment in order to find the maximum salinity tolerance limit, the salinity was gradually increased to 100%o, in the culture dishes having specimens at 40%0 saline water and it was noted that P nipponica specimens were alive even at 100%o salinity. It is concluded that comparatively lower sallinities are much more detrimental to the foraminiferal tests than higher salinities. Results are significant as the salinity response of benthic foraminifera is being used for environmental assessment.

Keywords

Benthic Foraminifera, Salinity Tolerance, Pararotalia nipponica, Culture Experiment, Retarded Growth, Dissolution, pH.

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Rajiv Nigam ¹, N. H. Hashimi ¹

Affiliations
1 Geological Oceanography Division, National Institute of Oceanography, Dona Paula, Goa - 403 004, IN

Abstract

No Abstract.

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