Carbonate lithofacies and depositional environments of the Lower Eocene Farafra Limestone, Farafra Oasis, Western desert, Egypt

Abstract

The Lower Eocene Farafra Limestone is subdivided into seven carbonate lithofacies. These lithofacies were deposited in three environments: off shore bank, bank interior and shelf slope. The lithofacies and the depositional environments in which they were deposited are: Lithofacies Environment Nummulitic-echinoidal wackestone Dolostone Ostrcod-miliolid wackestone Alveolina-miliolid packstone Bank interior Algal-alveolina-packstone Bioclastic packstone Bank interior Argillaceous foraminifera wackestone The off shore bank lithosfacies were deposited over and around structural highs (anticlines). Dolostones occupy the crets of the structural highs where they were formed by the dolomitization at mean sea level and/or in tidal zone. The Nummulitic-echnioidal wackestones were deposited around the structural highs in a warm shallow subtidal environments. The interior represents restricted marine waters it was enclosed between two off shore banks and was deposited in the structural low (syncline), hence the quiet water conditions and shallow depths. This interpretation stems from the facies associations which are mostly of ostracod-miliolid wackestone, alveolina-miliolid packstone and algal-alveolina packstone. The shelf slope lithofacies were deposited in a deeper setting away from the off shore banks at both extremes of the Farafra Oasis. The dominant lithofacies are bioclastic packstone and argillaceous foramineferal wackestone. The bioclasts are mostly of reworked fossils which were derived from the shallow off shore carbonate banks.