IN THE ESNA-IDFU REGION, NILE VALLEY, EGYPT 21 



inocerami (?) ; all the mosasaurs, plesiosaurs, ichthyosaurs ; all the dinosaurs and 

 pterodactyls, etc. were found to die out completely and to be replaced in the over- 

 lying Danian by a different fauna where Globigerina, Globigerinoides, Globorotalia, 

 Chiloguembelina, typical Tertiary molluscan and echinoderm fauna, and primitive 

 placental mammals made their appearance for the first time. This geologically 

 abrupt extinction of several typical representatives of Mesozoic life at the Maestricht- 

 ian-Danian boundary, which is followed by an equally abrupt appearance of definite 

 Cainozoic forms in the Danian rocks above, and which is documented in both the 

 marine and non-marine domains, clearly marks this boundary as the major biochrono- 

 logical line between the Mesozoic and the Cainozoic Eras. This is substantiated by 

 the fact that this major break is also accompanied by a pronounced change in the 

 generic and specific composition of many other groups such as the molluscs (Rosen- 

 krantz i960), the echinoderms (Poslavskaya & Moskvin i960), the coccolithophorids 

 (Bramlette & Sullivan 1961), as well as by a physical break of varying magnitude and 

 world-wide extent. On the other hand, many other species and genera survived this 

 change and continued their development from the Maestrichtian into the Danian or 

 even later stages. These were used by various authors as an argument for the 

 Cretaceous and/or the transitional character of the Danian fauna, and hence their 

 preference to include the Danian within the Cretaceous system. However, this does 

 not minimize the importance of the distinct stratigraphical break between the 

 Maestrichtian and the Danian, as survival of certain members of the organic life 

 across similar major faunal breaks is reasonably understood and clearly documented 

 in the history of the earth. Moreover, contrary to Brotzen (1959), the faunal break 

 between the Maestrichtian and the overlying Danian is definitely much more 

 pronounced and widespread than any known breaks between the Danian and the 

 overlying stages, or between the Maestrichtian and the underlying stages. Therefore, 

 the Mesozoic-Cainozoic contact is naturally placed at this boundary which is, as 

 described by Jeletzky (1962), " a natural boundary based on a unique and easily 

 recognizable, major biochronological event apparently reflecting some kind of a 

 radical, world-wide change in the physical regime of our planet ". 



Thus in the present study, the Danian is considered as the oldest stage of the 

 Tertiary system, and the Maestrichtian-Danian contact is taken to mark the 

 Mesozoic-Cainozoic boundary. This is in spite of the fact that various authors (e.g. 

 Brotzen 1959 and Yanshin i960) have strongly argued for, and continued to use the 

 term Danian in the sense of Desor, as the youngest stage of the Cretaceous system. 

 However, neither of these authors could provide any evidence against the definite 

 Tertiary character of the Danian fauna or the marked faunal break between the 

 Maestrichtian and the overlying Danian. Brotzen simply stated " To range the 

 Danian with the Cretaceous or the Tertiary is only a question of convention ", and 

 unjustifiably added " In my opinion no fundamental evidence has been adduced 

 which will necessitate changing the classical range of the Danian as the youngest 

 stage of the Cretaceous to the oldest stage of the Tertiary ". Yanshin built his 

 argument on a completely unsound basis and his paper is full of confusion and numer- 

 ous mistakes in matters of fundamental importance. 



