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

S. Chidambaram ¹, V. Vijayakumar ¹, K. Srinivasamoorthy ¹, P. Anandhan ¹, M. V. Prasanna ¹, S. Vasudevan ¹

Affiliations
1 Department of Earth Sciences, Annamalai University, Annamalai Nagar - 608 002, IN

Abstract

Hydrogeochemistry of a region is a reflection of the hydrodynamic processes, Lithological composition and physical constraints. Case study has been carried out in a varied lithologica] terrain with Archaean, Gondwana and Cretaceous rocks to unravel the hydrogeochemical process. The study area is around Perambalur region lying between Latitudes 11°O8OO" - ll°31OO" and Longitudes 78°35'00" - 78°5950" P_co2 values of water samples show wide variation in lithology, reflecting higher saturation index in carbonate minerals Mixing of water was witnessed in the Cretaceous formation Release of bicarbonate ions into the system is mainly derived from weathering of carbonate minerals reflecting lesser significance of silicate weathering. Thermodynamic equilibrium plot shows grouping of samples in the Kaolinite field with seasonal variation Saturation index (SI) for carbonate minerals is higher than silicate minerals Dilutions of samples are noted in the Archaean formation during Post-Monsoon season and migration of SI plume of carbonate minerals is towards southeast during Post-Monsoon season Geochemical reactions determining the water chemistry of the study area are also obtained by statistical analysis.

Keywords

Hydrogeochemistry, Lithological Differentiation, Saturation Index, Perambalur Area, Tamil Nadu.

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A. T. Rao ¹, K. Srinivasa Rao ¹, V. Vijayakumar ¹

Affiliations
1 Department of Geology, Andhra University, Visakhapatnam - 530 003, IN

Abstract

Basalts near Kateru, north of Rajahmundry in the East Godavari district and near Pangidi in the West Godavari district of Andhra Pradesh along the East Coast of India are of particular interest to investigators on account of their separation from the well known West Coast Deccan Basalts, localised around Bombay. The basalts around Rajahmundry are tholeiitic with equigranular, subophitic to ophitic textures. The principal constituents are plagioclase (An_55-56) and brownish nonpleochroic augite. The REE patterns of Rajahmundry basalts have a marked increased enrichment in LREE due to crustal contamination. The K-Ar age of Kateru basalts is 75.1±4.9Ma. The reported biochronostratigraphy of microfauna in the sediments closely associated in time and space with basalt flows in the Krishna-Godavari basin, east of Rajahmundry indicate that the age of basic volcanism is around 67 Ma. The lower limit of 70 Ma for the Kateru basalts supports that these basalts have evolved along with West Coast Deccan Basalts (69-65 Ma), where, the intensity of basic magmatism is more. The geological setting of Rajahmundry basalts with coastal sedimentary rocks indicate that the basic magmatism and sedimentation had taken place during the Cretaceous-Tertiary boundary.

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