Organic petrography and palynofacies of the Upper Cretaceous (Campanian-Maastrichtian) organic rich strata of the Quseir-Safaga Region, Eastern Egypt

Abstract

The Campanian-Maastrichtian organic-rich rocks in the Quseir – Safaga Region in the Eastern Desert of Egypt have growing economic importance. This economic importance is discussed in many of previous studies by many of different geological tools that lacked the petrographic examination of organic matter occurrence modes. The organic petrography provides the essential tools for microscopic analysis to study the organic matter that are applied for the first time in the present study. The palynofacies and organic petrography are used in the present study to investigate the nature of the organic matter and the paleoenvironmental settings that controlled their distribution in the Duwi and Dakhla formations in the Younis and Mohamed Rabah areas (Egypt). The study of dinoflagellate cysts allowed the identification of the biostratigraphically characteristic assemblages of the Campanian – Maastrichtian in the Eastern Desert including Assemblage II/I (in Duwi Formation) and Assemblage III (in Dakhla Formation) that were identified in Egyptian oil shales of this time range. The identified assemblages are correlated with local and regional studies to delineating the formal biozonation. The organic matter in the Duwi Formation comprises rich fluorescent amorphous organic matter, prasinophytes, sporomorphs, dinocysts as well as a minor terrigenous component of phytoclasts. In the Dakhla Formation, the fluorescent AOM is found to be highly mixed with Botryococcus in addition to prasinophytes and marine palynomorphs. The paleoenvironmental analysis indicates deposition in distal anoxic to proximal suboxic marine conditions with high paleoproductivity. The results are confirmed with the inorganic geochemical composition of redox sensitive elements. The analysis reveals that the Younis section is differentiated into two palynofacies types (proximal, suboxic high productivity in the Duwi Formation and distal anoxic in the Dakhla Formation). The Mohamed Rabah section, one palynofacies type is recognized that is proximal, suboxic high productivity. The principal component analysis is used to interpret the distribution of organic matter abundances. The kerogen types are distinguished based on the area percentages of the fluorescent organic matter and application of kerogen plots. The samples of both formations fall within oil prone kerogen type II. The spore coloration and measured vitrinite reflectance indicate immature kerogen in the studied sections. The organic matter in the studied rocks comprises hydrogen rich compounds that can be treated for direct composition or retorted to extract shale oil. The heavy metals concentrations are significant and present technology will increase its economic value.