A detailed study of the Esna shale in the Esna-Idfu type area in the Nile valley of upper Egypt proves it to be a group divisible into two formations, the underlying Sharawna shale of Maestrichtian age, and the overlying Owaina shale of Paleocene age, each comprising three distinct members. The two formations are separated by a sharp break and a thin but well-developed conglomerate marking the Mesozoic-Cenozoic contact. The base of the Esna group is the top of the Sibaiya (phosphate) formation of Senonian age. The top is at the base of the Thebes calcareous shale member of the Thebes formation of Eocene age, formerly considered part of the Esna shale. The collective treatment of these various rock units as a single formation in the past, assigned by some workers to the Cretaceous and by others to the Tertiary, is the source of the great confusion that has long existed.

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