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K. C. Rajasekaran ¹, V. Ram Mohan ¹

Affiliations
1 Geology Department, University of Madras, Madras, IN

Abstract

This note deals with twinned epidote found in epidote-biotite gneiss from Periya Soragai (Lat. N11°44'; Long. E77°55') west of Omalur, Salem District. The volume percent of the different minerals in the rock is: quartz-29%, plagioclase (27% to 29% An)-27%, biotite (pleochroic from pale yellow to greenish-brown)-26%, epidote (non-pleochroic)-16% and opaque oxide-2%. Few of the epidote grains are found to be twinned (Fig. 1).

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K. Selvaraj ¹, V. Ram Mohan ¹, M. P. Jonathan ², S. Srinivasalu ³

Affiliations
1 Department of Geology, School of Earth and Atmospheric Sciences, University of Madras, A C College Campus, Chennai - 600 025, IN
2 Centro de lnvestigaciones en Ciencias de la Tierra, Universidad Autonoma del Estado de Hidalgo, Ciudad Universitaria, Carretera Pachuca-Tulancingo, Pachuca, Hidalgo, C Postal 42184, MX
3 Departrnent of Geology, Anna University, Chennai - 600 025, IN

Abstract

The study of SPOT (1988) and IRS-1C (1998) images along with topographic maps (1928 and 1969-70) indicates that the wetland of Vedaranniyam has undergone significant landform modifications over a period of 70 years (1928-1998). Changes in shape and extent of the Mullippallam and Serattalaikkadu creeks, migrating confluence of stream Koraiyar towards north, development of mangrove vegetation, progradation and retrogradation of shoreline and increasing number of salt pans are determined and quantified. The study shows that fluctuations in the discharge of river flows and sediment loads associated with NE monsoon intensity and human interference through salt pan and agricultural activities are manly responsible for the dynamic changes observed in the area.

Keywords

Coastal Landforms, Fluvial Processes, Human Activity, Remote Sensing, Vedaranniyam Wetland, Tamil Nadu.

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K. Selvaraj ¹, V. Ram Mohan ²

Affiliations
1 Department of Geology, School of Earth and Atmospheric Sciences, University of Madras, A.C. College Campus, Chennai - 600 025, IN
2 Present address: Ocean Science & Technology Ceil (Marine Geology and Geophysics), Mangalore University, Mangalagangothri, Mangalore - 574 199, Karnataka, IN

Abstract

Surface sediment samples collected from 42 locations up to a water depth of 53 m during pre-NE monsoon (September, 1 995) and post-NE monsoon (April, 1996) seasons in the innershelf region, off Kalpakkam, were analysed for textural parameters, calcium carbonate and organic matter. Grain size distribution shows that the innershelf is carpeted with a mosaic of sand and silty sand with minor amounts of clay (0-4%). The analysed sediments are characteristically very poorly and poorly sorted, and dominantly positively skewed with very leptokurtic and very platykurtic nature. The occurrence of relict sediments in the form of coarse sand deposit around 19th km from the present shoreline has been identified as a palaeoshoreline. Bivariate plots of grain size parameters reveal that the sedimentary depositional environment is influenced dominantly by river/dune/beach conditions. A linear patch of coarse sand with higher concentration of CaC03 (>15%) and very low organic matter (<0.4%) at a depth around 50-53 m confirms the existence of the palaeoshoreline, formed probably during Holocene low sea level. SEM photomicrographs also support the occurrence of energy enviroment related to shoreline.

Keywords

Size analysis, Cac0³, Organic matter, SEM, Palaeoshoreline, Mid-Holocene, Sea Level, Kalpakkam, Tamil Nadu coast.

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K. Selvaraj ¹, V. Ram Mohan ², S. Srinivasalu ², M. R. Jonathan ², R. Siddartha ²

Affiliations
1 Ocean Science & Technology, Cell (Marine Geology and Geophysics), Mangalore University, Mangalagangothri - 574 199, Karnataka, IN
2 Department of Geology, School of Earth and Atmospheric Sciences, University of Madras, A.C. College Campus, Chennai - 600 025, IN

Abstract

Two sediment cores collected from the Ennore Creek, southeast coast of India, were studied for sand-silt-clay contents, CaC0₃, organic matter and nondetrital trace metals in order to understand the geochemical processes controlling the distribution of metals including anthropogenic factors, if any. Core 1 from the intertidal region with sandy sediments shows lower metal contents, except for the top oxic layer, when compared to core 2, consisting mostly of silty sand with significant percentage of clay and showing higher concentration of metals. The sediments of core 1 show an oxidized upper layer where metals are mobilized and diffused from less oxidized deeper layers due to early diagenetic processes. While Mn, Fe, Ni, Co, Zn and Cr are diagenetically modified, anthropogenic processes seem to influence Pb, Cd and, to some extent, Cr and Zn. Discharge of wastes from the nearby located thermal power plant, fertilizer (phosphate) industry, electroplating industries, and sewage are identified as additional possible sources for these metals. Detrital elements (Si - and Al) do not show any relation with the metals studied, except Fe and Al in core 1. Textural changes at three subsurface depths represented by silty sand (15,40 and 50 cm) in core 1 and clayey sand (10,32.5 and 55 cm) in core 2 are probably correlatable with the low rainfall intensity suggesting past drought conditions in the study area. A distinct increase in concentrations of nondetrital trace metals Pb, Cr, Zn and Cd at a depth of 37.5 cm in core 2 is probably related to the beginning of intense industrialization around 1970s in the area under investigation.

Keywords

Sediment Cores, Nondetrital Trace Metals, Early Diagenesis, Anthropogenic Factors, Ennore Creek, Tamil Nadu Coast.

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N. V. Vladykin ¹, S. G. Viladkar ², T. Miyazaki ³, V. Ram Mohan ⁴

Affiliations
1 Institute of Geochemistry SB RAS, Irkutsk-33, Box 4019, RU
2 Geology Department, St Xavier's College, Mumbai-400001, IN
3 Graduate School of Science and Technology, Niigata University, Niigata 950-2181, JP
4 Department of Geology, University of Madras, Chennai-600025, IN

Abstract

Benstonite-Ba-Sr carbonatites are found only in two localities in the world the Murun massif in Siberia and Jogipatti in Tamil Nadu, South India. The specific feature of these carbonatites is high BaO (20-35%) and SrO (up to 10% as in the Murun carbonatites) concentrations. These carbonatites jointly with calciocarbonatite varieties occur in caibonatite-alkaline complexes of Siberia and South India. However, carbonatites of South India and Siberia differ in terms of the chemical composition, especially the trace and rare earth element contents. In South India (Tamil Nadu area), carbonatites are found in three alkaline massits Samalpatti, Sevathur, and Elagiii. Benstonite carbonatites are found only in the Samalpatti massif as a small dyke. In the Murun massif carbonatites are separated from the silicate rocks and occur as a residual silicate-carbonate complex. It comprises microclinites, pyroxene-microclines, quartz-microcline- pyroxene-calcites, which contain calcite carbonatites and charoite rocks as schleiren and dykes. Benstonite carbonatites form a horizontal body of 40 m thick in the southwestern part of the complex. We examined and compared the geological and geochemical features of these two areas where Bensonite occurs in association with other carbonatites and discuss their origin. The Indian carbonatites crystallized as the plutonic phase while Siberian ones formed in the near-surface area and effused on the Earth's surface.

Keywords

Benstonite, Carbonatites, Geochemistry, Sevathur, Samalpatti, Tamil Nadu.

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