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

R. Ramesh ¹, S. K. Bhattacharya ¹, K. Gopalan ²

Affiliations
1 Physical Research Laboratory, Ahmedabad 380 009, IN
2 National Geophysical Research Institute, Hyderabad 500 007, IN

Abstract

Stable isotope ratios of hydrogen, carbon and oxygen in tree cellulose have been recently demonstrated as potential indicators of past climate, However, a number of problems remain to be solved before isotope dendroclimatology can be used for routine reconstruction of palaeoclimate. Here we review the existing Literature, with a special reference to the Indian context and identify key problems that deserve immediate attention.

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V. Subramanian ¹, G. Biksham ², R. Ramesh ²

Affiliations
1 School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, IN
2 Institute of Oceanography, McGill University, Montreal, CA

Abstract

An attempt is made to evaluate the environmental geology of non-Himalayan rivers of India. These twenty river basins including eleven medium basins together drain nearly 25 per cent of the sub-continent. The annual transport of suspended sediments and dissolved salts by these rivers have been estimated to be around 370 million tonnes and 61 million tonnes respectively. The rate of physical erosion among these basins range from 799 tonnes/km²/yr to 16 tonnes/km²/yr. Similarly, chemical erosion ranged from 110 tonnes/km²/yr to 22 tonnes/km²/yr.

Among the rivers considered, the chemical composition of water indicates that Cauvery carries a large silica load (39 ppm), while the TDS is low (172 ppm), whereas Sabarmati has the highest TDS (352 ppm). Krishna waters show the highest alkalinity. In all the rivers, conductivity shows good correlation with TDS. Sediment chemistry indicates that Cauvery river sediments are most siliceous while that of Godavari are least siliceous. In both these cases, average SiO₂ is higher than the Indian average river sediment. Similarly, Fe in southern river sediments is very high while P is very low compared to the Indian or world average. Apparently local geology (Shield area hard rocks in southern India and Deccan Traps in central India) control the water and sediment characteristics of the peninsular rivers.

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R. Ramesh ¹

Affiliations
1 Physical Research Laboratory, Ahmedabad, IN

Abstract

No Abstract.

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Pratul Kumar Saraswati ¹, R. Ramesh ²

Affiliations
1 Department of Earth Sciences, I.I.T., Powai, Bombay 400076, IN
2 Physical Research Laboratory, Navrangpura, Ahmedabad 380009, IN

Abstract

Developments in stable oxygen and carbon isotope studies of the sediments from oceanic realm has established their potential use as stratigraphic markers. Whereas, other schemes of stratigraphic classifications for the Cenozoic sediments of Kutch are available, this paper attempts to establish the stable isotope stratigraphy of a part of the sequence. It is observed that the δ¹⁸0 and δ¹³C variation significantly correspond to the chronostratigraphic units of this area. The negative δ¹³C of the Kakdian Stage (Berwali Series) shifts characteristically to positive values in the Babian Stage (Berwali Series) and then swings back to negative values in the Bermoti Series. The Kakdian Stage and the Bermoti Series, both having negative δ¹³C, can be differentiated by their respective δ¹⁸O range.

Keywords

Stable Isotopes, Eocene-Oligocene, Stratigraphy, Kutch.

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T. R. Venkatesan ¹, R. Ramesh ¹

Affiliations
1 Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, IN

Abstract

A procedure is outlined for plotting histograms taking the experimental errors into consideration. This is illustrated with an example. The Fortran program is also given.

Keywords

Histograms, Analytical Uncertainties.

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Jyotiranjan S. Ray ¹, R. Ramesh ¹

Affiliations
1 Physical Research Laboratory, Ahmedabad 380 009, IN

Abstract

A fluid-rock interaction model for treating the stable carbon and oxygen isotopic variations in altered carbonatites is presented and illustrated with an example using data from the ferrocarbonatites of Amba Dongar, Gujarat. The Amba Dongar ferrocarbonatites appear to have been altered by a fluid of magmatic origin at 100 to 200°C contrary to an earlier suggestion of meteoric groundwater alteration at ∼50°C.

Keywords

Isotope Geology, Ferrocarbonatite, Fluorite, Fluid-Rock Interaction Model, Carbon and Oxygen Isotopes, Amba Dongar, Gujarat.

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M. Prithviraj ¹, R. Ramesh ²

Affiliations
1 Earth System Science Division DST, New Delhi - 110 016, IN
2 Institute for Ocean Management Anna University, Chennai, IN

Abstract

No Abstract.

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S. G. Viladkar ¹, R. Ramesh ², R. K. Avasia ¹, P. B. Pawaskar ³

Affiliations
1 Department of Geology, St. Xavier's College, Mumbai - 400 001, IN
2 Physical Research Laboratory, Navrangpura, Ahmedabad - 380 009, IN
3 Bhabha Atomic Research Centre, Trombay, Mumbai, IN

Abstract

It is noteworthy that Amba Dongar carbonatite complex has both intrusive and extrusive phase carbonatites. The stratified tuff with components of both carbonatite and nephelinite have been recently traced in western part of Amba Dongar complex. In this preliminary report we present trace and rare earth elements data and C and O isotopes of these tuffs. The C and O isotopes of the least altered tuff falls within the mantle box while the remaining samples plot in the narrow field of 16-20% in oxygen. These values are explained using simple model of water-Rock interaction.

Keywords

Carbonatites, Extrusive Phase, Amba Dongar, Gujarat.

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M. G. Yadava ¹, R. Ramesh ¹

Affiliations
1 Physical Research Laboratory, Navrangpura, Ahmedabad - 380 009, IN

Abstract

Stable carbon and oxygen isotope vanations in speleothems collected from four locations in India, viz , Gupteswar (Orissa), Dandak (Chhattisgarh), Sota (Uttar Pradesh), and Akalagavi (Karnataka), and spanning various periods within the last ˜3400 years with different growth rates (0 09 to 1 34 mm/yr), have been compared In this paper we investigate the causative mechanisms for the observed variations and the spatial coherence in the isotope signals, and discuss their similarities and differences with other sirmiar high-resolution monsoon proxy records We note that (I) monsoon rainfall, and not the cave temperature, exerts a dominant control over both the carbon and oxygen stable isotope variations, (11) the oxygen isotoprc trend during 1500 400 years ago in the Indian and Omanian speleothems are in phase, and (111) dilution due to dead carbon is limited to less than 15 %.

Keywords

Speleothems, Southwest monsoon, Rainfall, Stable isotopes, Radiocarbon, Varves, Paleomonsoon.

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Kaustubh Thirumalai ¹, Arvind Singh ², R. Ramesh ²

Affiliations
1 Jackson School of Geosciences, University of Texas, Austin, TX - 78713, US
2 Physical Research Laboratory, Ahmedabad - 380 009, IN

Abstract

MATLAB^TM is a powerful, easy to use, software package suitable for many mathematical operations, which finds plenty of scientific applications. One such application is the fitting of trend lines for a given data set so as to interpret the relationship of the variance of the parameters involved. We provide here a code in MATLAB^TM that performs the weighted linear regression with (correlated or uncorrelated) errors in bivariate data which can handle 'force-fit' regression as well.

Keywords

Weighted Linear Regression, Correlated Errors, Force Fit, Trend Line, Bivariate Regression.

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Jyotiranjan S. Ray ¹, R. Ramesh ¹

Affiliations
1 Physical Research Laboratory, Navrangpura, Ahmedabad 380009, IN

Abstract

Accurate analysis of coexisting calcite and dolomite for δ¹³C and δ¹⁸O is generally hindered by the difficulty in the physical separation of these minerals. The difference in the reaction rates of calcite and dolomite with phosphoric acid, has been used to chemically separate these carbonates. Previously established procedures are only suitable for samples containing 1:1 calcite-dolomite pairs. However, these are sometimes tedious and time-consuming. Using mixtures of calcite and dolomite, two different selective acid extraction procedures (for reactions at 25°C), one for calcite-rich and the other for dolomite-rich carbonates, have been developed. Reduction of grain size (to 37μm - 45μm) increased the reaction rate and hence decreased the total reaction time to a reasonable interval (≤72 hours for dolomite). Applying these procedures, δ¹³C and δ¹⁸O of calcite and dolomite/ankerite of carbonatites from Amba Dongar and Sung Valley carbonatite complexes of India were measured and their temperatures of crystallization determined. Accurate isotopic compositions of individual carbonates of calcite-dolomite mixtures can be determined for geological interpretations by these procedures.

Keywords

Stable Isotopes, Carbonate Mixtures, CO₂ Extraction Technique, Calcite, Dolomite, Ankerite, Carbonatite, Amba Dongar, Sung Valley.

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