Anhydrite, gypsum and halite evaporites of Middle Miocene age occurring in the Gulf of Suez area constitute more than 50% of the total rock components. They are intercalated mainly with shales and also subordinate carbonate and sandstone layers. Examination of several evaporite samples under both binocular and petrographic microscopes reveals the presence of inclusions of various types hosted by gypsum crystals. Solid inclusions are composed mainly of minute calcareous particles, fine pyrite crystals and residual organic matter, while liquid inclusions, which are more frequent, exist in a uniphase or biphase state. A light hydrocarbon in the form of oil or gas constitutes one of these phases, while the other is a brine. Most of these inclusions are of primary origin and have been developed during the growth of the hosted minerals. Based on the assemblage of these inclusions, it can be assumed that the evaporitic environment of deposition, with its reducing condition and high salinity, is favourable for the generation of oil from accumulated organic matter. Also, the presence of a carbonate mineral trapped by gypsum indicates the possible mixing of marine water with a brine of restricted occurrence.

This paper describes the use of heavy minerals and the characteristics of quartz grains in the study of three exploratory wells (149 core samples) in the northern Western Desert, Egypt. The studied sandstones are characterized by a predominance of tourmaline, zircon, rutile, anatase. epidote, garnet, monazite. staurolite and chlorite, in decreasing order of abundance. In general, there is no distinctive heavy‐mineral variation between Jurassic and Lower Cretaceous sands. Examination of the frequency distribution of the different types of inclusions in the quartz revealed that abundant rutile needles reflect a metamorphic terrane and a plutonic environment. Abundant tourmaline, microlites and devitrified magmatic relicts reflect acidic intrusive/extrusive parent rocks. The abundance of rutile with apatite and zircon is interpreted as being derived from host quartz of various parent rocks. The alteration in some inclusions (segmented rutile needles, spotted apatite and dark zircon) suggests possible dynamic disturbance of the area, resulting in the introduction of inclusions and devitrified and/or altered primary solid inclusions. It is concluded that the Jurassic and Lower Cretaceous sandstones studied were formed in areas characterized by an arid climate. These conditions led to the decomposition of both unstable and metastable heavy minerals.

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