• Facies, dissolution seams and stable isotope compositions of the Rohtas Limestone (Vindhyan Supergroup) in the Son valley area, central India

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    • Keywords

       

      Dissolution seams; Rohtas Limestone; stable isotopes; diagenesis

    • Abstract

       

      The early Mesoproterozoic Rohtas Limestone in the Son valley area of central India represents an overall shallowing-upward carbonate succession. Detailed facies analysis of the limestone reveals outer- to inner-shelf deposition in an open marine setting. Wave-ripples, hummocky cross stratifications and edgewise conglomerates argue against a deep marine depositional model for the Rohtas Limestone proposed earlier. Stable isotope analysis of the limestone shows that δ13C and δ18O values are compatible with the early Mesoproterozoic open seawater composition. The ribbon limestone facies in the Rohtas Limestone is characterized by micritic beds, each decoupled in a lower band enriched and an upper band depleted in dissolution seams. Band-wise isotopic analysis reveals systematic short-term variations. Comparative enrichment of the heavier isotopes in the upper bands is attributed to early cementation from sea water and water derived from the lower band undergoing dissolution because of lowering of pH at depth. The short-term positive shifts in isotopic compositions in almost every upward gradational transition from a seamed band to a non-seamed band support the contention that dissolution seams here are of early diagenetic origin, although their formation was accentuated under overburden pressure.

    • Author Affiliations

       

      S Banerjee1 S K Bhattacharya2 S Sarkar3

      1. Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai - 400 076, India
      2. Physical Research Laboratory, Ahmedabad, Navrangpura, Ahmedabad - 380 009, India
      3. Department of Geological Sciences, Jadavpur University, Kolkata - 700 032, India
    • Dates

       
  • Journal of Earth System Science | News

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