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

R. Nagarajan ¹, J. S. Armstrong-Altrin ², R. Nagendra ³, J. Madhavaraju ⁴, J. Moutte ⁵

Affiliations
1 School of Civil Engineering, Sastra University, Thanjavur - 61 3 402,, IN
2 Centro de Investigaciones en Ciencias de la Tierra, Universdad Autonoma del Estado de Hidalgo, Crudad Universitaria, Carretera Pachuca-Tulancingo km 4 5, Pachuca, Hidalgo 42 1 84, MX
3 Department of Geology, Anna University, Chennai - 600 025, IN
4 Institute do Geologia, Estacion Regional del Noroeste, Universidad Nacional Autonoma de Mexico, Apart Postal 1039, Hermosillo, Sonora 83000, MX
5 Centre SpiNC, Ecole des Mines, 158 cours Fauriel, F 42023, Sant-Etienne, FR

Abstract

Petrographic, major, trace, and rare earth element compositions of quartz arenites, arkoses, and siltstones of Neoproterozoic Rabanpalli Forrnation of Bhima Basin have been investigated to understand the provenance. The quartz arenites, arkoses, and siltstones have large variations in major element concentrations. For example, quartz arenites and arkoses contain the hlgher Si0₂ (average with one standard deviation being 97±1,73±2,respectively) and lower Al₂O₃ (0 95±0 4, 9 6±O 9, respectlvely) concentrations than siltstones (SiO₂=64±4, A1₂0₃=14±1), which is mainly due to the presence of quartz and absence of other Al-bearing minerals in relation with rock types. This is also supported by our petrography, since quartz arenites and arkoses contain significant amount of quartz relative to feldspar and lithic fragments. The observed low CIA values and A-CN-K diagram suggest that the sedimentary rocks of Rabanpalli Formation have undergone K-metasomatism.

The Co, Ni, Cr, Ba, Zr, Hf, and Th values are higher in siltstones than quartz arenites and arkoses. The EU/EU^*, (La/LU)_en, La/Sc, Th/Sc, Th/Co, Th/Cr, Cr/Th ratios, and Cr, Ni, V, and Sc values strongly suggest that these sediments were mainly derived from the felsic source rocks. This interpretation is also supported by the Th/Sc versus Sc bivariate and La-Th-Sc triangular plots. The rare earth element (REE) patterns of these rocks also support their derivation from felsic source rocks. Further more, these rocks exhibit higher LREE/HREE ratio (8±4) and a significant negative Eu anomaly (0 77±0 16), which indicate the felsic igneous rocks as a possible source rocks.

Keywords

Geochemistry, Paleoweathering, Provenance, K-Metasomatism, Sandstone, Bhima Basin, Karnataka.

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N. Gladwin Gnana Asir ¹, S. Ramasamy ², J. S. Armstrong-Altrin ³, J. Madhavaraju ⁴, V. Stephen Pitchaimani ²

Affiliations
1 People's Action for Development, 2/29, Sebastian Kovil Street, Vembar - 628 906, IN
2 Sedimentology Lab, Department of Geology, University of Madras, Chennai - 600025, IN
3 Centre de Investigaciones en Ciencias de la Tierra, Universidad Autdnoma del Estado de Hidalgo, Ciiidad Universitana, Carretera Pachuca-Tulancingo km. 4.5, Pachuca, Hidalgo, 42184, MX
4 Universidad Nacional, Autonoma de Mexico, Institute de Geologia, Estacion Regional del Noroeste, Hermosillo, Sonora, MX

Abstract

An 8.8m of consolidated core obtained below 20m of unconsolidated marly sediments near the Tuticorin coast was subjected to detailed stratigraphic, petrographic and geochemical analyses. A lithological succession with eight minor Litho-Units in ascending order has been established: Shell limestone, lower sandy shell limestone, calcareous conglomerate, middle sandy shell limestone, algal limestone, upper sandy shell limestone, calcareous sandstone and calcrete. The petrographic types are mostly the variants of wackestone, boundstone, arenite and calcrete. CaO is high in shell limestone, algal limestone and sandy shell limestone and proportionately SiO₂ is low in these litho-units. Algal limestone is enriched in MgO content, The conversion of high Mg-calcite to low Mg-calcite, aragonite inversion as well as mixed zone diagenetic setting resulted in depletion of both δ¹³C and δ¹⁸O, The petrographic evidence and assemblage of the juvenile gastropods, pelecypods, bryozoans, algae and benthic foraminifers suggest a fluctuating inner neritic to a moderately high saline lagoonal depositional environment. The absence of sparry calcite indicates an early marine to mixed zone diagenetic settings and the shell limestone unit experiences a moderate burial diagenesis while the upper units experience a shallow burial diagenesis. A Late Tertiary age is assigned to the shell rich limestone unit.

Keywords

Depositional And Diagenetic Environments, Petrography, Stable Isotopes, Shallow Core, Tuticorin Coast, Tamil Nadu.

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J. S. Armstrong-Altrin ¹, J. Madhavaraju ², S. Ramasamy ², N. Gladwin Gnana Asir ²

Affiliations
1 Centro de Investigaciones en Clencias de la Tierra, Universidad Autonoma del Estado de Hidalgo, Ciudad Universitaria, Carretera Pachuca-Tulancingo km 4 5, Pachuca, Hidalgo- 42184, MX
2 Department of Geology, School of Earth and Atmospheric Sciences, University of Madras, Guindy Campus, Chennai - 600 025, Tamil Nadu, IN

Abstract

Quartz grains from Kudankulam Formation were studied using Scanning Electron Microscope(SEM), which brought out eighteen microtextures. The quartz grams of Kudankulam Formation show different types of conchoidal fracture, arcuate steps, V-shaped patterns, pits and sub angular to Sub-Rounded outline. The presence of conchoidal fracture and arcuate steps suggest that these quartz grains were derived from the nearby crystalline source. The microtextures such as V-shaped patterns, pits, straight and curved scratches are characteristic of marine environment.

Keywords

Quartz Grains, Microtextures, Kudankulam Formation, Provenance, Depositional History, Tirunelveli District, Tamil Nadu.

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