44 UPPER CRETACEOUS-LOWER TERTIARY FORAMINIFERA 



and that the Paleocene-Eocene boundary was differently interpreted by different 

 authors. 



C. Summary of the Succession 



The Upper Cretaceous-Lower Tertiary succession in the Esna-Idfu region is 

 naturally divided into four main lithological units which are easily recognizable in the 

 field and are arranged from the base upwards as follows : 



i. A lower arenaceous unit composed mainly of sandstones, and passing into 

 variegated shales at its top through various intercalations of shaly sand- 

 stones, sandy shales, shales and clays. The base of this unit is nowhere 

 visible in the region, but can be seen unconformably overlying the basement 

 complex at a distance of about 75 kms. to the east and about 100 kms. to the 

 south. This unit is about 500 m. thick, but a maximum thickness of 80 m. 

 only crops out in the Esna-Idfu region. 



2. An alternating succession of broadly extended phosphate lenses (approaching 



the form of regular beds), marl with flint nodules, chert bands and oyster 

 limestone, which has a maximum thickness of about 10 m. 



3. A lutaceous unit about 240m. thick, composed mainly of shales, but with marly 



and chalky intercalations. 



4. An upper calcareous unit composed of a small thickness of calcareous shales at 



its base, passing upwards into chalky, marly and siliceous limestones which 

 constitute the main part of this unit. Only the basal 60 m. or so crop out in 

 the Esna-Idfu region, while to the north and west the unit reaches a thick- 

 ness of about 340 m. 



The lowermost sandstone unit, which was commonly referred to as " the Nubian 

 sandstone " was recognized by Youssef (1957), in the Kosseir area, as a formation and 

 was named the " Nubia sandstone ". 



Ghorab (1956) considered the variegated shales overlying the Nubia sandstone and 

 underlying the lowermost phosphate bed in the Kosseir area as a separate formation 

 and named it the " Quseir formation ". Youssef (1957) suggested the name " Kossier 

 variegated shales " for the same formation. However, because of the small thickness 

 outcropping of both the sandstones and the shales in the Esna-Idfu region, and because 

 the two facies pass imperceptibly into one another, these variegated shales are here 

 included within the Nubia sandstone, and the two facies are considered as one forma- 

 tion which is here collectively termed " the Nubia sandstone and variegated shale ". 



A succession of phosphates, marls and limestones overlies the Nubia sandstone and 

 variegated shale, with a general conformable relationship, except for local thinning 

 out, diastems or even disconformities. This succession, although of a comparatively 

 small thickness (not exceeding 10 m.), has a considerable lateral extent, and forms a 

 sharply distinctive and a conveniently mappable rock unit. Thus it is here consider- 

 ed as a distinct formation and assigned the name " Sibaiya phosphate ". Ghorab 



