Lithostratigraphy, petrography, and geochemistry of the Eocene–Oligocene rock succession, Wadi Arhab area, North Eastern Desert, Egypt

Abstract

The present study recorded for the first time, an occurrence of Oligocene basaltic plugs in Beni-Suef Governorate, Egypt. In addition, Egyptian alabaster was discovered in the study area, further the well-known ancient area around the Cavern of Wadi Sannur. In this work, the lithostratigraphy, structure, petrography, and geochemistry including TGA and DSC were studied. In addition, the thermal effect of the basaltic magma on the Eocene carbonates that covered most of the area, caused the formation of the Egyptian alabaster in the region. The Eocene succession represents different stages in age (late Middle–Late Eocene). Their outcrops are disconformably overlain by the basaltic plugs extruded along the NW–SE fault trend which is parallel to the Red Sea graben which was formed in the Oligo–Miocene Period. Petrographically, the Eocene rocks show ten microfacies types indicating that deposition of Eocene carbonates in the subtidal shallow marine environment except for microfacies of the Egyptian alabaster shows that the precipitation is related to the basaltic thermal effect and related hydrothermal waters within open cavities or karstic systems in the Eocene carbonate. The chemical analysis showed that SiO₂, Al₂O₃, MgO, Fe₂O₃, and CaO are of high content as major oxides, while Sr and Ba are of high content in the basaltic plugs as trace elements. TG analysis shows that basaltic rocks in the present study are suitable for conserving high-temperature thermal energy because they do not exhibit any thermal events when exposed to thermal influences by DSC between 30 °C and 1000 °C. Unlike both Egyptian alabaster and recrystallized limestone which are not suitable for maintaining high temperatures between 695 °C and 965 °C and decompose into CaO and CO₂ due to the decarbonization of the calcite mineral.