Electrical, mineralogical, geochemical and provenance of Cretaceous black shales, Red Sea Coast, Egypt

Abstract

Detailed mineralogical and geochemical studies were carried out on the middle members of the black shales of the Duwi Formation (Quseir–Safaga province) to define their source rock, paleo-weathering, pollution impact and provenance of the sources. The studied black shales are highly fossiliferous and fissile. They are texturally classified as phosphatic marly mudstone microfacies. The black shale mineral composition is mainly composed of calcite, apatite, quartz, pyrite and clay minerals. The average values of Cu, Ni, Zn, Cr, V, As and Se and the ratios Rb/Sr and Cr/Ni in black shale are enriched compared to those of the Post-Archean Australian Shale (PAAS) values. Electrical properties of samples were measured using a non-polarizing electrode, at room temperature (∼18°C), and relative atmospheric humidity of (∼35%), in the frequency range from 42 Hz to 5 MHz. The changes in electrical properties were argued to be due to the change in mineral composition. Generally, the electrical properties of rocks are changed due to many factors such as grain size, mineral composition, grain shape and inter-granular relations between grains. The dielectric constant decreases with frequency, and increases with conductor concentration. Also, the conductivity increases with the increase of conductor continuous paths between electrodes.