抄録
The fabrics and presence of celestite in the carbonate cements in the reefal limestone of Gebel El Rusas Formation and the sabkha sequences of the Abu Dabbab Formation (Middle Miocene) suggest deposition in a hypersaline vadose regime. The recorded carbonate cements are represented by paleoflowstone crusts; spheroidal and hemispheroidal structures and giant plaeoaragonite ray-crystals deposited in fenestrae and as crusts within the Miocene sediments.
The carbonate cements occur in the form of polycrystalline calcite pseudospar and fibrous calcite resulting from paramorphic replacement of aragonite in Mg-poor fresh water vadose regime. Traces of native sulfur is formed together with secondary gypsum and calcite in the surficial layer of the Abu Dabbab evaporites. It is formed in a localized microenvironment in the fresh water vadose regime due to bacterial activity on sulfate deposits.
