Petrographic Studies of the Alamein Dolomite (Lower Cretaceous) in El-Razzak Oil Field, Western Desert, Egypt

Abstract

The origin and environment of deposition of the Alamein Dolomite in the El-Razzak Oil Field have been investigated by means of petrographic, chemical and X-ray analysis. The studied rocks are composed of dolomite with variable amounts of calcite, with anhydrite and iron oxide as minor minerals. Alamein Dolomite has been formed by replacement of limestones under a variety of conditions either penecontemporaneously or soon after deposition, or later through the action of ascending solution of either meteoric water or by hydrothermal solutions. Dolomitization took place in shallow, warm, Mg-rich environment under favourable pH, Eh, salinity, and temperature conditions. The low SiOs content, absence of fossils, and the association of anhydrites with dolomites reflect a restricted, shallow-marine, low energy environment, interrupted in parts, by high-energy level environment in which microsparites and sparites were formed.