Growth rate and life span of Eocene/Oligocene Nummulites tests: inferences from Sr/Ca ratio |
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| Authors: | S. Sarangi,A. Sarkar,M. M. Sarin,S. K. Bhattacharya,M. Ebihara,& A. K. Ray |
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| Affiliation: | Department of Applied Geology, Indian School of Mines, Dhanbad 826 004, India,;Physical Research Laboratory, Ahmedabad 380 009, India,;Faculty of Science, Tokyo Metropolitan University, Tokyo 192–03, Japan,;Department of Geology, Presidency College, Calcutta 700 073, India |
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| Abstract: | The problem of growth rate and life span of Nummulites foraminifers, attaining giant sizes during the Eocene, has been addressed by analysing their Sr/Ca ratio across the Eocene/Oligocene Boundary (EOB) of Kutch, western India. The Eocene ratio (˜ 1) rapidly decreases during the Oligocene (˜ 0.5) and is coincident with the extinction of most of the Eocene Nummulites species, a rapid enrichment of δ18O and decrease in both test size and species diversity across the boundary. The high Sr/Ca ratio in Eocene foraminifers can be explained by their rapid growth under a favourable climatic condition. The climatic deterioration (e.g. δ18O cooling) across the boundary and during the early Oligocene possibly forced the Nummulites to adopt a slower growth rate (and stunted growth). The rapid growth of the Eocene Nummulites indicates that the giant sizes of these protists need not necessarily involve a large life span. |
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