I2S Ml DDLE ALBIAN STRATIGRAPHY 



Subzone. The cristatum Subzone as here defined, therefore, includes sediments 

 grouped with the Upper Gault. 



As Breistroffer has pointed out (1947 ; 48-50), Dipoloceras cristatum and the other 

 contemporary species of this genus are of widespread occurrence. They are known 

 in sequences as far removed from each other as the Anglo-Paris basin, the Malagasy 

 Republic and Zululand, Russia and Texas, that is, in more than one ammonite 

 faunal province. The well-marked period of erosion of Middle Albian sediments in 

 the Anglo-Paris basin which occurred during the cristatum Subzone, is just as well 

 marked in the Malagasy Republic (Besairie & Collignon 1956). Although not 

 specifically stated by Young (1966) there are signs of a similar break in Texas. It is 

 also possible that there is a break in the sequence in Peru (Benavides-Caceras 1956). 

 In an entirely different faunal province still, the occurrence of Gastroplites cantianus 

 in Bed VIII at Folkestone and in the lower part of the Gastroplites Zone in Canada is 

 extremely important (e.g. Jeletsky 1964 ; Table 1, 1968). In Canada there is a 

 definite break in the ammonite sequence although apparently not in the sedimentary 

 sequence (Jeletsky in litt.), for the mcconneli Zone which contains genera such as 

 Arcthoplites, Cymahoplites and Cleoniceras, both known from the mammillatum Zone 

 of the old world (Casey 1961c ; 167) is definitely of Lower Albian age. A similar 

 ammonite faunal gap involving the whole of the Middle Albian appears to exist in 

 Alaska (Imlay i960 : 1961) and California. Imlay's Cleoniceras (Grycia) presents no 

 difficulty here because it does not possess umbilical bullae and almost certainly 

 belongs to Beudanticeratinae. In effect, by taking the base of the Upper Albian to 

 coincide with the base of the cristatum Subzone and its provincial equivalents, it is 

 possible to arrive at a common point of division between the two substages capable of 

 recognition in the local successions of each county. 



(iv) THE ZONAL GROUPING (Table 1, p. 10) 



(a) The Zone of Hoplites (H.) dent at us 



As defined here this Zone comprises the Subzones of H. (I.) eodentatus, L. lyelli and 

 H. (H.) spathi. This represents virtually the total range of the closely related 

 morphological group of Hoplites represented by the index species H. (H.) dentatus. 

 In the eodentatus Subzone, this species is not typically developed, but in fact H. (I.) 

 eodentatus is a direct transition between the earlier Pseudosonneratia and H. (H.) of 

 the dentatus group. This group dies out at the top of the spathi Subzone, although 

 Hoplites (H.) continues onwards into the loricatus Zone above. With some modifi- 

 cation, this is almost a return to the old concept of the interruptus Zone in Barrois' 

 and Jukes-Browne's sense. 



The Zone is geographically widespread represented in sediments both condensed 

 and uncondensed. The hoplitinid faunal province by the spathi Subzone can be 

 shown to have extended from the western border of asiatic Russia, south to the 

 northern margin of Tethys now represented in the Caucasus mountains. The 

 boundary then runs along the northern side of Tethys westwards to France. The 

 land area flanking the east side of the Atlantic rift system which existed at this 

 time (cf. Carey 1958) apparently formed the western boundary, although the situation 



