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Characterization of Paleosol at Isotopic Level and Its Implication to Past Climate and Vegetation: A Case Study from Rayka Section Near Mahi River, Gujarat.

Kumar, Anurag (2014) Characterization of Paleosol at Isotopic Level and Its Implication to Past Climate and Vegetation: A Case Study from Rayka Section Near Mahi River, Gujarat. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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    Abstract

    Quaternary fluvial sequence is wide spread in India. The Quaternary deposits in Gujarat, Western India show abundant development of calcrete in paleosol. Precipitation of carbonate generally takes place near the vadose zone above the water table. It takes 1000 of years to form these pedogenic carbonate. Carbonate nodules preserve the signature of vegetation and rainfall that prevailed during the formation of the nodule through the isotopic exchange with soil CO₂ and soil water. Analysis of δ¹³C of these carbonate nodules give the type of vegetation that grew in that region. Similarly the δ¹⁸O values show variations in rainfall during the time of formation of these carbonate nodules. Selection of samples from calcrete plays important role in construction of paleo climate. There can be variation in texture of carbonate at mesoscopic (e.g. highly pedogenised and less pedogenised) level and microscopic (e.g. micrite and microsparite) level. Carbonate nodules were used for the isotope study. Both microsparitic and micritic grains were observed in the thin section of soil carbonate (SC) nodules. The microsparitic grains, which had undergone recrystallization, showed variation in δ¹³C value between -5.8‰ to -2.9‰. Whereas the variations in d18O values observed were between -4.1‰ to -1.1‰. The variations for d13C in micritic grains which preserves the pristine isotopic character were between -6.2‰ to -3.3‰ and for δ¹⁸O the variations were between -3.8‰ to -1.6‰. The d13C values for soil organic matter (SOM) varied from -24.5‰ to -19.8‰. Lower δ¹³C value for SOM is observed at two places L1-5 and L1-4 with value of -14.7‰ and -11.2‰. The variation in the both δ¹³C of calcrete and soil organic matter indicates that the abundance of C3 – C4 plants changed with time. On the other hand the variations in the δ¹⁸O values imply change in the intensity of monsoonal rainfall.

    Item Type: Thesis (Masters)
    Additional Information: Supervisor: Dr. Prasanta Sanyal
    Uncontrolled Keywords: Gujarat; India; Isotopic Level; Mahi River; Paleosol; Past Climate; Rayka Section; Vegetation
    Subjects: Q Science > QE Geology
    Divisions: Department of Earth Sciences
    Depositing User: IISER Kolkata Librarian
    Date Deposited: 08 Jan 2015 17:12
    Last Modified: 08 Jan 2015 17:12
    URI: http://eprints.iiserkol.ac.in/id/eprint/178

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