The marginal marine conditions of the variegated shales were followed by a shallow sea in Late Campanian time in which phosphate beds intercalated with clay, limestone and chert beds were deposited. In the belt which extends from Dakhla Oasis in the west (Abu Tartur Plateau) to Qusier in the east, the phosphate beds are well developed and assume economic importance. They are named Duwi (Phoshate) or Formation.

To the south of this belt, the phosphate beds do not form an important element in the formation and become indistinguishable from the overlying Dakhla Shale. The Late Campanian ammonites: Libycoceras, Baculites and Solenoceras are usually recorded at the contact. The Dakhla (228 m in its type section) is made up of black to dark green shales and marls which carry biostromes of Exogyra overwegi of Maastrichtian age. These are followed upward by a thick shale section with minor calcareous sandstone beds carrying Cardita libyca of Early Paleocene age.