28 UPPER CRETACEOUS-LOWER TERTIARY FORAMINIFERA 



tricarinata, and abundant Rugoglobigerina, Hedbergella and Globigerinelloides species, 

 which indicate an Upper Senonian, pre-Maestrichtian age, and the entire absence of 

 typical Maestrichtian forms, represent one of several enigmatic problems about the 

 true stratigraphical position of the Thanetian, and the geological history of England 

 during the Cretaceous-Tertiary transition period. The existence of mixed Senonian 

 and Danian fauna in the type Thanetian may be explained by the suggestion that the 

 whole planktonic foraminiferal content is reworked from previously existing Senonian 

 and Danian strata, although no Danian deposits have yet been recorded anywhere in 

 the British Isles. This may be substantiated by the record, in the type Thanetian, 

 of a meagre calcareous nannoplankton assemblage which also occurs in the " G. 

 pseudomenardii Zone of Trinidad " (Bramlette & Sullivan 1961). On the other hand, 

 it could suggest that while the Senonian forms are reworked from the underlying 

 chalk, the Danian ones are possibly indigenous ; hence the type Thanetian may 

 include strata which are equivalent to the type Danian. This conclusion is doubted 

 here owing to the absence of a typical Danian macrofauna and fauna of benthonic 

 Foraminifera. However, the author refrains at present from taking any decision 

 about the true stratigraphical position of the Thanetian until its type sections are 

 examined in detail and correlated with the other type sections of the various stages 

 of the Paleocene, and with the Paleocene in other parts of the world. Nevertheless, 

 the Thanetian of England is probably different from the Thanetian in the Paris Basin ; 

 while Arctica morrisi marks the top of the former, it is supposed to underlie the 

 latter. This simply points to the fact that the true stratigraphical position of the 

 Thanetian, like that of the Montian, is not yet clearly understood and that the vague 

 use of these terms in Paleocene stratigraphy is far too dangerous at the moment. 



Loeblich & Tappan (1957ft) also mentioned the difficulty in correlating the Sparna- 

 cian, as it is represented in its type section by non-marine facies. However, they 

 mentioned that as the non-marine Woolwich and Reading Beds and the underlying 

 marine Thanet Beds of England, are considered as deposits of one and the same 

 sedimentary cycle (Stamp 1921 ; Haynes 1955), the non-marine type Sparnacian 

 is more probably related to the Paleocene. Moreover, they stated that " Until 

 marine strata referable to the Sparnacian can be obtained this problem is difficult 

 to solve. It may represent both late Palocene and early Eocene time ". However, 

 on their correlation diagram they considered the Sparnacian as the upper substage 

 of the Landenian, although Feugueur (1955, 1962, 1963) has constantly advocated 

 the time-stratigraphic equivalency of the type Sparnacian and the lower Ypresian. 



This brief discussion clearly indicates the great difficulty in correlating the various 

 stages and substages of the Paleocene, because of the non-marine, or very near-shore 

 facies of most of the type sections, and the uncertainty about their true chronological 

 relationship. It also indicates that the assignment of the various planktonic 

 foraminiferal zones by Loeblich & Tappan (1957a, b), Bolli (1959), Bolli & Cita 

 (1960a, b), Hofker (1961a, 1962a) and various other authors, to the Montian, Thanet- 

 ian, Sparnacian, or Landenian, is rather arbitrary and is not based on any proper 

 correlation with the type sections. 



