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

P. M. Mohan ¹, K. Shephard ¹, N. Angusamy ¹, M. Suresh Gandhi ¹, G. V. Rajamanickam ¹

Affiliations
1 Department of Industries and Earth Sciences, Tamil University, Thanjavur - 613 005, IN

Abstract

Quaternary landforms between Vedaranyam and Rameshwaram on the east coast of India show a wide range from inland sand dune, flood plain, estuary, delta, cusp, beach, coastal dune, barrier ridge, mud flat, tidal creek to mangrove. The study area has been classified into inland, beach and offshore regions to evaluate the variation in the distribution of grain size and the depositional environments. 147 sediment samples were collected using hand augur along the beach (53) and inland (37) environments, and by Van Veen grab in the offshore area (57). Grain size analysis indicates that the area may have extended approximately 25 km towards inland from the present-day low water mark. In those days, the coast must have developed by almost similar processes as acting at present in the nearshore environment, and the sea level oscillation may have been significant in the past. Further, based on the present day rate of sedimentation, it is suggested that the study area may have developed within the last 1,50,000 years B.P.

Keywords

Quaternary Sedimentation, Coastal Geomorphology, Palk Strait, Tamil Nadu.

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N. Angusamy ¹, G. Victor Rajamanickam ¹

Affiliations
1 Department of Earth Sciences, Tamil University, Thanjavur - 613 005, IN

Abstract

Frequency distribution of heavy minerals along the southern Tamil Nadu coast from Mandapam to Kanyakumari shows selective deposition of heavies with respect to their densities. In Kanyakumari sector in the south, the heavies are concentrated in coarser sands, in the central Tuticorin sector in medium sands, and in the northern Mandapam sector in fine sands. Weight percentage distribution of heavies shows poor concentration at Mandapam that can be ascribed to strong progradational activity and wave-divergent conditions. A higher concentration of heavies in the ephemeral stream mouths in Tuticorin sector is due to the arcuate nature of the coastline, strong convergence of orthogonals and a basinal structure, all of which enable trapping of sediments carried by littoral currents. The poor concentration of heavies in Manappad sector, despite wave-convergent condition, is due to the straight alignment of the coastline without any arcuate bays. The enrichment of heavies in Kanyakumari sector is attributable to the arcuate coastiine and a downwarped basinal structure.

Keywords

Heavy Minerals, Beach Sands, East Coast, Tamil Nadu.

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P. Udayaganesan ¹, N. Angusamy ², A. R. Gujar ³, G. V. Rajamanickam ⁴

Affiliations
1 Alagappa Government Arts College, Karaikudi - 630 003, IN
2 Fortesque Metals Group, Perth, AU
3 National Institute of Oceanography (Council of Scientific and Industrial Research) Dona Paula - 403 004, IN
4 Sri Sairam Group of Institutions, Chennai, IN

Abstract

Quartz grain surface micro textures of 12 samples collected from the beach were examined under scanning electron microscopy to understand the role of coastal processes on their transportation and deposition. The study area has been divided into three sectors on the basis of drainage, geomorphology and nature of the beach and shelf topography. Surface textures of the northern sector display an array of mechanical features like conchoidal fracture, V marks and impact pits, indicating the dominance of mechanical processes. However, silica precipitation in the form of globules indicates an added influence of chemical processes in the Northern sector. The presence of chemical features in northern sector, where energy level is high, corroborates the addition of quartz grains from paleo-sediments, from the nearby Tertiary and Cretaceous formations. Central sector quartz grains display the signatures of chemical and mechanical processes. The presence of step like furrows in southern sector is an indicator of fluvial low energy conditions, and supplements the role of littoral currents in depositing the quartz grains along the coastal region.

Keywords

Surface Texture, Quartz, SEM, Central Tamil Nadu Coast.

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