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

D. N. Yadav ¹, M. M. Sarin ², S. Krishnaswami ²

Affiliations
1 Bhabha Atomic Research Centre, Trombay, Mumbai - 400085, IN
2 Physical Research Laboratory, Earth Science Division, Ahmedabad - 380 009, IN

Abstract

Geochemical analysis of groundwater samples and brines from the Sambhar Salt lake shows a predominance of NaCl with respect to total salt content (TDS), which varies from 0.5 to -400 g/L. All brine (lake + shallow subsurface) samples indicate a Na-Cl type alkaline solutions with pH varying from 8.5 to 10. All this suggests a general provenance for halite or dissolution of desiccated salt minerals in the catchment and drainage areas of the lake. Adjacent groundwaters are mostly neutral Na-Cl type with TDS ranging from 0.5 to 13 g/L. In contrast to groundwaters, the river waters from Roopangarh and Mendha reflect that out of the TDS, the major ions constitute Na, Alk and Cl with an average equivalent Na/Cl ratio of 2.7, indicating dissolution of Na from silicate weathering of rocks. However, the lake water composition overwhelms the river water upon mixing during the recharge period. A complete annual wetting and drying cycles of evolution of lake brine shows generation of Na-Cl type of brine with steady increase in major ions except Ca and Mg ions which decrease in successive stages of evaporation. Relative change in Na and Cl ions is also observed during the late stage of evaporation at or beyond halite saturation stage. Observation of such chemical change in brine composition is in line with the identification of salt minerals in lake sediments and salt encrustation by XRD technique.

In present-day hydrologic set-up, the estimated salt inventory in lake is _10⁶ tons as compared to riverine input of 6x10⁴ tons and an upper limit of aeolian input of about 5xl0⁴ tons. Such an estimate indicates that majority of salt is derived from the recycling and re-solution of salt encrustation from the lake bed during recharge period.

Keywords

Hydrogeochemistry, TDS, Nacl, Brines, Annual Wetting and Drying Cycles, Evaporation, Brine Evolution, Salt Encrustation, Aeolian Salt Input, Recharge Period, Sambhar Salt Lake, Rajasthan.

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D. N. Yadav ¹, M. S. Chauhan ², M. M. Sarin ³

Affiliations
1 Bhabha Atomic Research Centre, Trombay, Mumbai - 400 085, IN
2 Birbal Sahni Institute of Palaeobotany, 53 University Road, Lucknow - 226 007, IN
3 Earth Science Division, Physical Research Laboratory, Ahemdabad - 380 009, IN

Abstract

A 15 m deep sedimentary core from Jagmotha swamp in northeastern Madhya Pradesh has been analyzed for reconstruction of Late-Quaternary vegetation and climate change based on distribution of major/Trace elements, organic carbon, nitrogen and pollen grains contained in the sediments. The combined geochemical and palynological results indicate a cool and dry climate between 6000 to 5000 yrs BP representing a tree savannah type vegetation followed by warm and moist climate between 5000 to 3000 yrs BP. Such a drastic change in climate promoted tropical mixed deciduous forests in the region. Subsequently, between 3000 to 1200 yrs BP, the climatic condition got further improved with enhanced precipitation in the region marked by the advent of sal tree in the forest floristics. Since then, the climate has been inferred conducive for development of modern sal forests in the region.

Keywords

Palaeoclimate, Palaeovegetation, Late-Quaternary Period, Major/Trace Element Geochemistry, Organic Carbon and Nitrogen, C/N Ratio, Pollen Frequency.

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