Glauconite facies developed sequentially in the Abu Tartur Plateau (Egypt) during the Late Cretaceous

Glauconite-rich Cretaceous sediments occur in the Western Desert of Egypt and accumulated in shallow water during major transgressions and global warming intervals. This work introduces a sedimentological scenario for the vertical transition from black shales to evolved glauconite through a series of successive depositional episodes. These episodes started with the deposition of illite-rich claystone green beds at the top of the Quseir Formation, which were followed by grainy phosphorites and black shale. Glauconite pellets are scattered in the black shale and increase as a percentage vertically. After that, an illite-rich claystone layer at the top of the Quseir Formation was deposited. Later on, high-grade phosphorites were accumulated through the reworking and concentration of authigenic phosphate muds. These phosphorites were followed by the deposition of organic-rich black shale in a low-energy environment. With time, disseminated glauconite grains became scattered in the black shale or filled the bioturbation tubes. As the glauconite percent increased, it accumulated as interlaminations with black shale, and it is associated with siderite and coal pockets. Physical processes like exhumation, reworking and re-sedimentation led to the concentration of evolved glauconite. Rock samples have been collected, and petrographic, mineralogic, geochemical and X-ray analyses, an SEM investigation, and thin-section microscopy have been carried out. There are similar case studies of glauconites of shallow-water origin in the paleo-Tethyan area through the Late Cretaceous.