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

M. K. Bera ¹, Kasturi Bhattacharya ¹, A. Sarkar ², A. Samanta ², Kishor Kumar ³, Ashok Sahni ⁴

Affiliations
1 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur - 721 302, IN
2 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur -721 302, IN
3 Wadia Institute of Himalayan Geology, Dehradun - 248 001, IN
4 Centre of Advanced Study in Geology, Panjab University, Chandigarh - 160 014, IN

Abstract

Oxygen isotope composition (δ¹⁸O) of fossil bone and tooth enamel phosphate (bioapatite) is an important tool for estimating the isotopic composition of past environmental water. Lack of analytical facility was a hindrance for studying such bioapatites in spite of large number of fossil materials reported from various geological ages in India. We have established in our laboratory, based on available methods, the chemical procedure for extraction of very small amount (<1000 μg) PO₄ ^-3 from bioapatite and on-line mass spectrometric measurement of its δ¹⁸O composition by high temperature (∼1450 °C) pyrolysis. The achieved precision is ∼± 0.3 ‰ similar to obtained elsewhere, with interlaboratory calibration showing excellent agreement of standard phosphates. Inferred δ¹⁸O values of environmental water, based on the analysis of teeth and bones of sharks, fish and terrestrial mammals from the Paleogene successions of the northwest sub-Himalayan and the Peninsular India show strong correspondence with animal habitats. The freshwater δ¹⁸O values are much depleted having range similar to modern monsoon precipitation. However, owing to our small dataset it is not possible at this stage to infer about the existence of monsoon over the Indian sub-continent during the Eocene-Oligocene time.

Keywords

Phosphate, Pyrolysis, Oxygen Isotope, Monsoon.

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