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      https://www.ias.ac.in/article/fulltext/jess/126/02/0017

    • Keywords

       

      Pumice; basalt; sea rafting; Eocene; Carlsberg Ridge; Vastan lignite mine; India.

    • Abstract

       

      The recognition of pyroclasts preserved in sedimentary environments far from its source is uncommon. We here describe occurrences of several centimetres-thick discontinuous basaltic pumice lenses occurring within the Early Eocene Vastan lignite mine sedimentary sequence, western India at two different levels –one at ~5 m and the other at 10 m above a biostratigraphically constrained 52 Ma old marker level postdating the Deccan Volcanism. These sections have received global attention as they record mammalian and plant radiations. We infer the repetitive occurrence of pumice have been sourced from a ~52–50Ma MORB related to sea-floor spreading in the western Arabian Sea, most plausibly along the Carlsberg Ridge. Pyroclasts have skeletal plagioclase with horsetail morphologies ± pyroxene ± Fe–Ti oxide euhedral crystals, and typically comprise of circular polymodal (radii ≤10 to ≥30 μm), non-coalescing microvesicles (>40–60%). The pumice have undergone considerable syngenetic alteration during oceanic transport and post-burial digenesis, and are a composite mixture of Fe–Mn-rich clay and hydrated alteredbasaltic glass (palagonite). The Fe–Mn-rich clay is extremely low in SiO₂, Al₂ O₂, TiO₂ , MgO, alkalies and REE, but very high in Fe₂O₃, MnO, P, Ba, Sr contents, and palagonitization involved significant loss of SiO₂, Al₂O₃, MgO and variable gain in Fe₂O₃, TiO₂, Ni, V, Zr, Zn and REE. Bubble initiationto growth in the ascending basaltic magma (liquidus ~1200–1250◦C) may have occured in ~3 hr. Shortdistance transport, non-connected vesicles, deposition in inner shelf to more confined lagoonal condition in the Early Eocene and quick burial helped preservation of the pumice in Vastan. Early Eocene Arabian Sea volcanism thus might have been an additional source to marginal sediments along the passive margin of western India.

    • Author Affiliations

       

      Sarajit Sensarma1 Hukam Singh2 R S Rana3 Debajyoti Paul4 Ashok Sahni5

      1. Centre of Advanced Study in Geology, University of Lucknow, Lucknow 226 007, India.
      2. Birbal Sahni Institute of Palaeobotany, Lucknow 226 007, India.
      3. Department of Geology, HNB Garhwal University, Srinagar 246 174, India.
      4. Department of Earth Sciences, Indian Institute of Technology, Kanpur 208 016, India.
      5. Centre of Advanced Study in Geology, Panjab University, Chandigarh 160 014, India.
    • Dates

       
  • Journal of Earth System Science | News

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