6 MIDDLE ALBIAN STRATIGRAPHY 



de la base de l'Albien moyen, et la sous-zone de cristatum a la base de l'Albien superieur. Une 

 6tude de la m6de de deposition de l'Albien moyen en Angleterre montre qu'elle imite la deposition 

 de l'Albien infeYieur et Aptien, non pas celle-la de l'Albien superieur. L'auteur finit en passant 

 en revue la faune des ammonites. 



I. INTRODUCTION 



The Albian Stage terminating the Lower Cretaceous has been divided into Lower, 

 Middle, and Upper Substages. In England, the Lower Albian is represented within 

 the top beds of the Lower Greensand and its junction with the overlying clays of the 

 Gault ; the Middle Albian within the Gault, and by the Lower Gault where this 

 division is recognisable ; and the Upper Albian by the Upper Gault and the contigu- 

 ous Upper Greensand. Both the Middle and Upper Albian are represented within 

 the Red Chalk facies. In northern France and the Paris Basin there is a similar 

 lithological sequence, excluding a Red Chalk facies but including local lithological 

 units in various areas such as the Sables de Puisaye flanking the northern area of the 

 Massif of Morvan. This essentially common sequence reflects the closely comparable 

 depositional environment which existed in the area of the Anglo-Paris Basin during 

 Albian times. 



This Basin extended from the area of the Massif Central and the Vosges in the 

 south to the English Midlands (text-fig. 51). It was flanked on the west by the 

 Variscan massifs of Armorica and Cornubia, and on the east and north east by those 

 of the Rhine State Mountains and the Ardennes. Late Jurassic — early Cretaceous 

 deformation provided the basic structural pattern for Lower Cretaceous sedi- 

 mentation which achieved its greatest geographical extent during Albian times. 

 Middle Albian sedimentation followed this earlier pattern, but this changed in the 

 Upper Albian due to tectonic disturbances at its start. The Basin was linked with 

 the surrounding shelf seas north of the Ardennes, and with Tethys by means of the 

 Morvano- Vosges strait. These sea-ways provided important migration routes for 

 the fauna. 



In terms of absolute radiometric dates, the Albian is taken by Casey (1964 ; 199) 

 to commence at 106 my B.P., and is considered to have had a duration of 6 million 

 years. However, as that author clearly states, this is purely an arbitrary figure, the 

 Cretaceous being divided into twelve equal time units corresponding to the twelve 

 Stages. At present, therefore, there is no alternative but to use the relative units of 

 time implied in the zonal schemes based on the faunal succession. Of these schemes, 

 that based on the ammonites is the one which has been most thoroughly investigated, 

 and the one that has led to much difference of opinion both national and international. 

 A good deal of this disagreement is due to insufficient knowledge of the succession, 

 despite the considerable number of papers which have been published. 



Within the lengthy bibliography on the English Albian two major works stand 

 out ; the Memoir by Jukes-Browne (1900), and the Monograph by Spath on the 

 Albian Ammonoidea (1923-43). The work carried out before 1900 in certain cases 

 was truly excellent. For example, that of De Ranee (1868) and Price (1879, 1880) 

 at Folkestone, Newton (1897) at Okeford Fitzpaine, Dorset, and Keeping (1868) at 

 Upware, Cambridgeshire. All this earlier work is ably summarised by Price and 



