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

M.W. ALI-BIK, H.I.M. METWALLY, A.M.A. WALI, M.G. KAMEL

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.


Keywords


Gypsum; Lithofacies; Non-marine; Geochemistry

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DOI: http://dx.doi.org/10.1344/105.000002051

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Geologica Acta (ISSN-1695-6133)
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