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

N. H. Hashimi ¹, R. Nigam ¹, R. R. Nair ¹, G. Rajagopalan ²

Affiliations
1 National Institute of Oceanography, Dona Paula, Goa-403 004, IN
2 Birbal Sahni Institute of Palaeobotany, Lucknow-226 007, IN

Abstract

A new Holocene curve is generated for the western Indian continental margin. While constructing this curve careful selection of the dates were made by giving due considerations to the genetic characteristics of the dated material. This new curve shows a low at 100 m depth around 14,500 years BP and a rise to 80.m depth around 12,000 years BP showing a rate of ˜10m/1000 years which was followed by astillstand for about 2,000 years. From 10,000 to 7,000 years it rose at a very high rate (˜20 m/1000 years). Beyond 7,000 years BP it showed minor fluctuations.

Keywords

Holocene, Sea Level Fluctuation, Sea Level Curve, Arabian Sea, West Coast of India.

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R. Saraswat ¹, A. Deopujari ², R. Nigam ¹, P. J. Heniriques ³

Affiliations
1 Micropaleontology Laboratory, National Institute of Oceanography, Goa - 403 004, IN
2 St Xavier College, University of Mumbai, Mumbai - 400 032, IN
3 St. Xavier College, University of Mumbai, Mumbai - 400 032, IN

Abstract

The relationship between abundance (relative as well as absolute abundance) and morphology (size of the shell, number of chambers and proloculus size) of benthic foraminifera Epistominella exigua has been studied in a core to understand the influence of changing environmental conditions on its morphology and distribution. A total of 50 samples from the top 100 cm section of a gravity core collected from the southern Bay of Bengal Fan were used. The changes in abundance of E. exigua match well with variation in average proloculus size of E. exigua. An opposite relationship however, is observed between the abundance and size of E. exigua shells. The higher abundance corresponds with smaller E. exigua shells. Similarly, the increased E. exigua abundance matches with a decrease in the number of chambers. The increased abundance of E. exigua shows favourable conditions for its growth and survival. Thus the study indicates that during favourable conditions, while the number of chambers in the shells and the size of the shells of E. exigua decreases, more number of specimens have a larger proloculus. Since asexual reproduction results in megalospheric specimens with larger proloculus, smaller size and less number of chambers, it is inferred that E. exigua prefers an asexual mode of reproduction during favorable conditions. The findings can be used to apply morphological characteristics of E. exigua as a proxy to infer past climatic conditions.

Keywords

Benthic Foraminifera, Epistominella exigua, Morphology, Reproduction.

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