IN THE ESNA-IDFU REGION, NILE VALLEY, EGYPT 31 



of its index species, and its upper boundary is marked by the first appearance of the 

 sharply keeled Globorotalia assemblage, typified by G. velascoensis velascoensis 

 (Cushman) and G. pseudomenardii Bolli. 



3. An upper zone characterized by an assemblage of rugose Globigerina and 

 sharply-keeled and/or rugose Globorotalia species. In this zone, the tendency 

 towards the development of a marginal keel and/or a rugose surface which started 

 with the early representatives of Globorotalia in the Lower Paleocene, is fully 

 achieved. At the bottom of this zone the first known sharply-keeled Globorotalia, 

 represented by G. velascoensis velascoensis (Cushman) and G. pseudomenardii Bolli, 

 make their appearance. G. pseudomenardii dies out towards the middle but G. 

 velascoensis velascoensis continues to the top, where it dies out completely. Globoro- 

 talia velascoensis with its three subspecies, G. velascoensis velascoensis, G. velascoensis 

 parva, and G. velascoensis caucasica, represent the dominant forms of the zone which 

 is thus known as the G. velascoensis Zone. This zone is considered to represent the 

 Upper Paleocene in Mexico, in the Gulf and Atlantic Coastal Plains of the U.S.A., 

 in the Caribbian region, in Southern France, in Italy, in North Africa, in the Middle 

 East, in Pakistan-India-Burma region, in New Zealand and in the U.S.S.R., although 

 the characteristic species are not recorded in the type Upper Paleocene of Western 

 Europe (the Landenian) which is mainly of continental and lagoonal facies. However, 

 as previously mentioned, the sharply keeled Globorotalia assemblage of the G. 

 velascoensis Zone represents the maximum development of a continuous evolutionary 

 trend which started at the base of the Paleocene, typified by the bio-series : Globoro- 

 talia pseudobulloides^G. trinidadensis^G. uncinata uncinata^G. angulata angulata^- 

 G. angulata abundocamerata^-G. velascoensis velascoensis (Text fig. 15). This 

 continuous evolutionary sequence is paralleled by similar lineages throughout the 

 Paleocene, and proves that there are three distinct stages in the development of the 

 genus Globorotalia : the rounded stage, the truncated stage and the sharply keeled 

 stage. It also justifies consideration of these three stages as divisions within one 

 natural unit, hence the position of the G. velascoensis Zone as the Upper Paleocene and 

 the underlying two zones as the Middle and Lower Paleocene respectively. Analysis 

 of previously recorded planktonic Foraminifera in the Paleocene of different parts 

 of the world, shows the existence of these three stages, and thus substantiates the 

 division of the Paleocene proposed here. 



The Paleocene-Lower Eocene Boundary 



The fact that the Upper Paleocene in its type region is represented by non-marine 

 sediments, and that the planktonic Foraminifera in the type Lower Eocene are 

 hardly known, made it difficult to decide the position of the Paleocene-Lower 

 Eocene boundary with certainty. However, as previously suggested by Bolli 

 (1957a, 19596), Loeblich & Tappan (1957a, 6) and Bolli & Cita (1960a, 6), and as 

 reasoned above, this boundary is drawn at the top of the Globorotalia velascoensis 

 Zone, although Olsson (i960) included the latter zone within the Lower Eocene. 

 Analysis of the planktonic foraminiferal content of the G. velascoensis Zone shows 

 clearly that it has more species in common with the underlying Paleocene zones than 



