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      https://www.ias.ac.in/article/fulltext/jess/130/0060

    • Keywords

       

      Clay minerals; trace metals; river sediments; provenance; chemical weathering; mafic/felsic sources.

    • Abstract

       

      The clay fraction of sediments in the lower reaches of 15 rivers along the east coast of India showed high kaolinite followed by illite and smectite for the rivers dominantly draining the Archaean–Precambrian Terrain (APT), high smectite followed by illite and kaolinite for those draining the Deccan Trap Volcanic Terrain (DVT) and, high illite followed by kaolinite, smectite or chlorite for those draining through Mixed-Lithology Terrain (MLT). The CIA (Chemical Index of Alteration) and PIA (Plagioclase Index of Alteration) values, depletion of Ca, K, Na and Sr and enrichment of Al, Fe and Ti, high Rb/Sr and Th/U ratios of sediments relative to the Upper Continental Crust indicate moderate to intense chemical weathering on source rocks. The average composition of clays exhibits slight enrichment of Fe, Mg, Sc, V, Co, Cr and Ni and depletion of Nb, Zr, Hf, Y and Ta relative to the Post-Archaean average Australian Shale. The Cu, Zn and Pb contents were in the range ‘significantly polluted to moderately polluted’ in APT- and DVT-sediments. The plots of TiO$_{2}$ vs. Fe$_{2}$O$_{3}$+MgO, Th/Sc vs. Sc and La–Th–Sc showed sediment composition intermediate between granite and basalt, while the plots of TiO$_{2}$ vs. Zr, Th vs. Sc and V–Ni–Th indicate intermediate provenance between mafic and felsic sources. The mineralogy of the sediments indicates mixed sources, but their chemical composition is affected by weathering and the provenance is intermediate between mafic and felsic sources.

      $\bf{Highlights}$

      The clay fraction of the sediments in 15 rivers along the east coast of India showed

      $\bullet$ Mixed-mineral assemblages in accordance with dominant geology and chemical weathering.

      $\bullet$ High CIA and PIA, and low Ca, K, Na and Sr values indicating moderate to intense chemical weathering on source rocks.

      $\bullet$ Enriched transition metals and depleted high-field strength elements supporting dominance of mafic component.

      $\bullet$ Ratio–ratio plots of trace metals indicating intermediate provenance between mafic and felsic sources.

    • Author Affiliations

       

      SHAIK SAI BABU1 VENIGALLA PURNACHANDRA RAO1 NANNAPANENI SATYASREE1 RAVIPATI VENKATA RAMANA1 MEKALA RAM MOHAN2 SARIPOOT SAWANT2

      1. Vignan’s Foundation for Science, Technology and Research (VFSTR), Deemed to be Vignan’s University, Vadlamudi, Guntur 522 213, India.
      2. CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad 500 007, India.
    • Dates

       
  • Journal of Earth System Science | News

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