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

N. Rajeshwara Rao ¹, Neloy Khare ², P. Periakali ¹

Affiliations
1 Department of Applied Geology, University of Madras, Guindy College Campus, A.C. College Building, Chennai 600 025, IN
2 Antarctic Study Centre, Vasco-da-Gama, Goa 403 802, IN

Abstract

Studies on Recent foraminifera from inner shelf sediments of the Bay of Bengal, off Karikkattukuppam, near Chennai (latitude 13°04'N; longitude 80°17'E), revealed the presence of a rare foraminiferal species. Taxonomic observations reveal this spinose taxon to be Glandulina spinata Cushman and is reported herein for the first time from Indian waters. Available data suggest it to be a tropical, inner shelf dwelling taxon, with a preference for muddy substrate.

Keywords

Palaeontology, Recent, Foraminifera, Taxonomy, Inner Shelf, Bay of Bengal.

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S. G. D. Sridhar ¹, S. M. Hussain ², P. Periakali ¹, V. Kumar ³

Affiliations
1 Department of Applied Geology, University of Madras, Guindy Campus, Chennai - 600 025, IN
2 Department of Geology, School of Earth and Atmospheric Sciences, University of Madras, Guindy Campus, Chennai - 600 025, IN
3 Department of Geology, National College, Tiruchirappali - 620 001, IN

Abstract

The shallow marine and tropical ostracod taxon Kotoracythere inconspicua(Brady) is encountered from the surface sediments of Indian waters Fifty-Two sediment and bottom water samples were collected over an year, representing the four seasons, in a transect (depth 0-13 m) off Rameswaram, southeast coast of India. Living specimens of this species are found in all the seasons. Systematics and ecology of the species are presented Biogeographically, this taxon has an extremely wide distribution in tropical, littoral zones of all oceans, excepting east Pacific. Its wide geographic distribution is explained through currents and by passive dispersal by ships.

Keywords

Ostracoda, Ecology, Biogeography, Palk Bay, Indian Ocean.

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M. Sathyanarayanan ¹, P. Periakali ¹

Affiliations
1 Department of Applied Geology, University of Madras, Guindy Campus, Chennai - 600 025, IN

Abstract

Mineralogic, hydrogeologic and geochemical data of ultrabasic and Peninsular gneissic rocks of Salem covering an areal extent of about 194 km² around Salem magnesite mine area were employed to determine the source of solutes to groundwater and to assess the chemical weathering processes. The results indicate that the flux of dissolved solids from the abandoned mines are controlled by interaction between ultrabasic rocks and materials derived from local bedrock. Mass balance calculations indicate that dissolution of feldspar and ferromagnesian minerals releases Na, Ca and Mg. The average denudation rate was found to vary from 0.3 to 4.2 tons/km²/yr for a discharge of 5.3 × 10⁸1/yr, and from 0.5 to 8 tonnes/km²/yr for a discharge of 10 × 10⁵ 1/yr. Mineral solubility study of Mg-phase in the system shows that serpentine is the dominant Mg²⁺ contributor.

Keywords

Groundwater, Geochemistry, Ultrabasics, Peninsular Gneiss, Salem, Tamil Nadu.

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N. Lakshmi Narayana ¹, M. Sathyanarayanan ², P. Periakali ²

Affiliations
1 Geohouse, H.No.2-3-173, Road No.2, Adarsh Nagar, Nagole, Hyderabad - 500 068, IN
2 Department of Applied Geology, University of Madras, Guindy Campus,Chennai - 600 025, IN

Abstract

No Abstract.

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P. Periakali ¹, S. Eswaramoorthi ¹, S. Subramanian ¹, P. Jaisankar ¹

Affiliations
1 Climate Change Research Unit, Department of Applied Geology University of Madras, Guindy Campus, Chennai 600 025, IN

Abstract

Fourteen sediment samples collected from Pichavararn mangrove were analysed for grain size, organic carbon, sedimentary sulphur, calcium carbonate, Fe, Mn, Al, Cu, and Hg. Factor analysis was carried out to infer the mechanisms controlling the behaviour of metals. Four factors accounted for around 75% variance. Fe, Mn, and Hg are associated with organic carbon and fine fraction content of the sediments and loaded onto factor I whlch accounted for 33.6% variance. This is due to the complexation of Fe, Mn, and Hg with organic matter and the adsorption of these organo-metallic compounds onto the finer sediments due to their high surface/volume ratio and presence of surface charge. Factor 2 accounted for 18.6% variance and is loaded with CaCO₃, finer fraction, Al and Cu, implying contribution of Al and Cu from detritai clay minerals. The association of CaCO₃, with this factor is not clearly understood. Factor 3 is loaded with organic carbon and coarse fraction of the sediments and it accounted for 13.3% variance. The association of organic carbon with coarse fraction of the sediments could be either due to the Ca²⁺ and Mg²⁺ ions induced adsorption of organic matter onto mineral grains, or due to the presence of coarse vegetal debris. The fourth factor accounted for 9.8% variance and is loaded with sedimentary sulphur; no metal is associated with this factor. This explains that though sulphate reduction occurs in the surface sediments, it could not result in the burial of Fe, Cu, and Hg as their respective sulphides. This could be due to their back oxidation by Mn oxides present in the sediments where upon FeS is converted to Fe hydrous oxide, and Cu and Hg are released to the water column.

Keywords

Geochemistry, Sediments, Pichavaram Mangroves, Trace Metals, East Coast of India.

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P. Periakali ¹, S. Eswaramoorthi ¹, S. Subramanian ¹

Affiliations
1 Climate Change Research Unit, Department of Applied Geology, University of Madras, Guindy Campus, Madras- 600025, IN

Abstract

The sequential extraction of core sediment samples of Pulicat lake for the determination of exchangeable, carbonate-bound. Fe-Mn oxides-bound, and organic-bound fractions of Fe and Mn were carried out to study the remineralization of organic matter in the sediments. Iron and manganese oxides are highly depleted in the upper portion (0-18 cm) of the core due to their reduction during organic matter oxidation. The model calculations based on the solid phase organic carbon depth profile indicate an average accumulation rate for organic carbon in the Pulicat lake sediments to be 13.5 gC/m².yr. The average remineralization rate is 12gC/m².yr. This is around 89% of the organic carbon deposited in thc sediments. The remineralization of organic carbon in this lake sediment could release 16 x 10³ tonnes of CO₂ /yr.

Keywords

Organic Geochemistry, Carbon, Sequential Extraction, Trace Metals, Core Sediments, Pulicat Lake, Tamil Nadu.

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