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

S. Das Sharma ¹, D. J. Patil ¹, R. Murari ¹, K. Gopalan ¹, G. V. Nesterenko ²

Affiliations
1 National Geophysical Research Institute, Uppal Raod, Hyderabad-500007, IN
2 Vernadsky Institute of Geochemistry, Kosygin Street 19, Moscow-117075, RU

Abstract

No Abstract.

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B. Kumar ¹, S. Das Sharma ¹, M. Shukla ², M. Sharma ²

Affiliations
1 National Geophysicai Research Institute, Uppal Road, Hyderabad - 500 007, IN
2 Birbal Sahni Institute of Palaeobotany, Lucknow - 226 007, IN

Abstract

Carbon isotope records on carbonates from the Bhima basin are characterized by ¹³C enriched values (up to 4‰ PDB). These data are integrated with the available palaeontological records to suggest a Terminal Proterozoic (post - Varanger) age for the Bhima sediments. The carbon isotope compositions of Katamadevarhalli and Shahabad carbonates analysed in the present study exhibit two distinct trends. While the Katamadevarhalli carbonates show a positive trend, those from Shahabod display a negative trend from bottom to top, probably indicating long-term temporal trend of carbon isotope values.

Keywords

Chronostratigraphy, Carbonates, Carbon and Oxygen Isotopes, Bhima Basin, Terminal Proterozoic, Karnataka.

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S. Sarangi ¹, K. Gopalan ¹, A. B. Roy ², B. Sreenivas ¹, S. Das Sharma ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN
2 Jai Narayan Vyas University, Jodhpur - 342 00 1, IN

Abstract

Pb-Pb isochron age of carbonate rocks of the Jhamarkotra Formation of the Aravalli Supergroup from the Udaipur sector in Rajasthan has been measured for the first time as 1921±67 Ma (2σ). We consider this as a reset age, as it is indistinguishable from the earlier reported Rb-Sr isochron age of 1900±8O Ma for the Darwal Granite formed synkinematically with the Aravalli deformation. The depositional age of the Jhamarkotra carbonates could be 200-300 Ma older as suggested by the positive δ¹³C anomalies noted in these carbonate rocks.

Keywords

Pb-Pb Isochron Age, Carbonates, Aravalli Supergroup Rajasthan.

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P. Senthil kumar ¹, G. Parthasarathy ¹, S. Das Sharma ¹, R. Srinivasan ¹, P. Krishnamurthy ²

Affiliations
1 National Geophysical Research Institute, Uppal Road, Hyderabad-500 007, IN
2 Atomic Minerals Directorate for Exploration and Research, AMD Complex, Begumpet, Hyderabad-500 01 6, IN

Abstract

Carbonate veins up to few metres thick have been recognised in the E-W striking Salem-Attur deep fault zone which represents the eastern extention of the Moyar fault in the southern granulite terrane of India. X-ray diffraction, FTIR spectroscopy and chemical analyses show calcite, ankerite, siderite and benstonite as dominant minerals besides minor apatite and green biotite. Whole rock compositions show enrichment of light REE, Ba, Sr and Nb. C and 0 isotopic data determined for calcite (δ¹³C= -4.9 to -5.1%0 V-PDB and δ¹⁸0 = 9 to 9.2%0 V-SMOW) points to a mantle origin. The chemical characteristics therefore suggest that the carbonate veins have carbonatitic affinity. The FTIR spectra provide evidence for presence of H₂0 and CH₄ in addition to CO₂ in the carbonate minerals of these veins.

Keywords

Ferrocarbonatites, Benstonite, FTIR Spectroscopy, X-Ray Diffraction, Geochemistry, Isotopes, Tamil Nadu.

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