Integrated petrographic, mineralogical, and geochemical study of the Late Cretaceous-Early Tertiary Dakhla Shales, Quseir-Nile Valley Province, central Egypt: implications for source area weathering, provenance, and tectonic setting

Late Cretaceous-Early Tertiary shales of the Dakhla Formation of the Quseir-Qena Province, central Egypt, were analyzed for major and selected trace elements to infer their provenance, source rock paleoweathering intensity, and tectonic setting. The studied formation consists of a series of marls and shales and is subdivided into two members, namely Beida Shale Member at the top and Hamama Marl Member at the base. The Dakhla Shales are texturally classified as mudstones. Mineralogically, these shales consist mainly of smectite and kaolinite. Chemical analysis of the major and trace elements generally exhibits a uniform distribution throughout the Upper Maastrichtian-Lower Paleocene sediments. SiO2, Al2O3, and Fe2O3 contents are higher than the values reported for the post-Archaean Australian shale (PAAS), while TiO2 and Na2O contents are found to be lower. Bivariate plot of Zr versus TiO2 diagram indicates that intermediate to felsic igneous rocks constitute the main supplying source rock. Average chemical index of alteration (CIA), plagioclase index of alteration (PIA), and chemical index of weathering (CIW) values (81, 92, and 93 %, respectively) imply intermediate to intense weathering of the source material in a semiarid climate. The bivariate discriminant function diagram reveals an active continental to passive margin setting for the Dakhla Shales. The developed soils were transported by rivers to the depositional basin. The inferred tectonic setting for the Late Cretaceous-Early Tertiary Dakhla Shales in Quseir-Qena Province is in agreement with the tectonic evolutionary history of central Egypt during the Late Cretaceous-Early Tertiary.