Facies and geochemistry of non-marine gypsum, EMISAL, Egypt

Authors

  • M.W. ALI-BIK Geological Sciences Department, National Research Centre, Dokki, Cairo, Egypt
  • H.I.M. METWALLY Geological Sciences Department, National Research Centre, Dokki, Cairo, Egypt
  • A.M.A. WALI Geology Department, Faculty of Science, Cairo University, Egypt
  • M.G. KAMEL Academy of Scientific Research and Technology, Cairo, Egypt

Keywords:

Gypsum, Lithofacies, Non-marine, Geochemistry

Abstract

Diverse gypsum facies in terms of crystal size and morphology are deposited in a shallow, non-marine, sulfateenriched, semi-closed, perennial evaporite basin. These gypsum facies were deposited in intimate association with cyanobacterial mats. Facies analyses and geochemistry revealed two distinct primary facies, based on gypsum fabric; massive selenite, and laminated gypsum varieties. The massive selenite facies is composed of clusters of single and twinned crystals along (100), with upward pointing re-entrant angle. The laminated gypsum varies from rhythmically laminated grass-like selenite to gypsum microbialite (stromatolite). The change from massive selenite to laminated gypsum facies implies fluctuation in lateral and vertical salinity profiles, seasonal brine concentrations and wind action. Post-depositional changes in the form of dissolution, slight to moderate crystal deformation and recrystallization to anhydrite are evaluated. We develop a qualitative model for the depositional basin and facies distribution in order to simulate ancient analogues.

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