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

S. Ramasamy ¹, J. Madhavaraju ¹, J. Armstrong Altrin Sam ¹

Affiliations
1 Sedimentology Lab, Department of Geology, School of Earth and Atmospheric Sciences, University of Madras, Guindy Campus, Chennai 600 025, IN

Abstract

Recent field study of Gondwana sediments in the Palar basin near Chennai brings to light the occurrence of assorted size of boulders of extraneous source in argillaceous siltstones. These boulders are regarded as glacial in origin. It is interpreted that icebergs carried such boulders into a pro-glacial lake. Melting of the icebergs resulted in dropping of boulders into the depositional environment. The present study discusses the depositional environment and paleoclimate that prevailed during the deposition of these exotic boulders.

Keywords

Depositional Environment, Paleoclimate, Dropstones, Gondwana Sediments, Icebergs, Pro-Glacial, Palar Basin, Tamil Nadu.

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J. Armstrong Altrin Sam ¹, S. Ramasamy ¹, A. Makhnach ²

Affiliations
1 Sedimentology Laboratory, Department of Geology, University of Madras, Guindy Campus, Chennai - 600 025, IN
2 Institute of Geological Sciences, National Academy of Sciences of Belarus, Kuprevich Street 7, 220141 Minsk, BY

Abstract

The results obtained from stable isotope study of Neogene carbonates of Kudankulam, Tamil Nadu show negative values for δ¹³C, which range from -2.6‰ to -9.7‰ PDB. The δ¹⁸O values range from -4.5‰ to -11.4‰ PDB. The depleted nature of the δ¹⁸O and δ¹³C values suggests the strong effect of meteoric diagenesis in the Kudankulam carbonates. Standard bivariate plots of δ¹⁸O versus δ¹³C for carbonate materials/rocks helped to identify their depositional and diagenetic environments. Petrographic study points out large-scale emplacement of ferroan sparry calcite cement into vugs and other leached cavities.

Keywords

Limestones, Miocene, Petrography, Geochemistry, Stable Isotopes, Diagenesis, Tamil Nadu.

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S. Ramasamy ¹, J. Armstrong Altrin Sam ¹

Affiliations
1 Sedimentology Laboratory, Department of Geology, University of Madras, Chennai - 600 025, IN

Abstract

Rhodoids are laminated algal nodules generally found in shallow marine environment. Algal crusts and nodules are poorly exposed between Kudankulam and Sattankulam in the coastal area near Cape Comorin. The thickness of the bed of algal limestone varies from 0.5 to 1.5 m. The occurrence of abraded rhodoids with lack of terrigenous material suggests moderate to high energy depositional condition. The present study of the rhodoids, points out that the Neogene tectonic activity has played a significant role for the development of algal limestone and rhodoids in the study area.

Keywords

Palaeoenvironment, Rhodoids, Neogene Carbonates, Tamil Nadu.

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