Facies and depositional environment of the Holocene evaporites in the Ras Shukeir area, Gulf of Suez, Egypt

The Holocene evaporite sequence in the Ras Shukeir area conformably overlies marine shell banks and cross-bedded to graded-bedded beach sands and gravels. The evaporite sequence is represented by gypsum-anhydrite layers that are interbedded with mudstone layers. Field and petrographic investigations of the evaporite deposits revealed two facies types, laminated evaporite facies (primary) and nodular to enterolithic anhydrite facies (diagenetic). The laminated evaporite facies is subdivided, from the bottom to top, into regular laminated evaporite, chevron gypsum-algal micrite laminations and wavy algal laminated evaporite. Based on their textures and fabrics, the regular and wavy laminated evaporite facies are interpreted as primary deposits in a coastal lagoon and salina environment. The chevron gypsum-algal micrite facies formed by the growth of chevron gypsum at the sediment-water interface within a shallow subtidal lagoonal environment that was characterized by extensive benthic algal mats. The nodular to enterolithic anhydrite facies is secondary and formed diagenetically within a siliciclastic supratidal sediment. Some of the laminated evaporite facies have been diagenetically altered in a supratidal sabkha environment as evidenced by the following: (1) the partial formation of nodular evaporite instead of laminated evaporite; (2) disruption of gypsum laminations by plant roots and rootlets as well as by precipitation of lenticular gypsum on the root wall; and (3) partial dissolution of halite laminae and the formation of wavy anhydrite laminae. Consequently, the Holocene evaporites in the Ras Shukeir area were deposited in a shallow semi-closed to closed basin that was separated from the Gulf of Suez trough. Changing sea level led to progradation of the evaporite facies from subtidal to intertidal lagoon and salina to a supratidal sabkha.