IN THE ANGLO-PARIS BASIN 143 



(b) The Structural Controls on Deposition 

 in southern England (text-fig. 52) 



The Variscan Wessex Basin of Kent (1949 ; 99) and its continuations into the 

 Weald and across the Channel into France subsided fairly steadily throughout the 

 Jurassic roughly in pace with the sediments which infilled it. At the end of the 

 Jurassic and at the opening of the Cretaceous Period, a strong phase of folding 

 and faulting occurred which in Dorset must have included fold amplitudes of well 

 over 1000 feet (>305 m.). The resulting basin of sedimentation was very greatly 

 reduced in area in comparison with that of the Jurassic. The history of Lower 

 Cretaceous sedimentation in southern England is the progressive erosion of the 

 resulting land area of Jurassic sediments and their redeposition within the basin. 

 This basin was by now restricted to the area of the Weald proper and eastern Hamp- 

 shire, and the English Channel flanking the Isle of Wight and Sussex. That the 

 deformation was essentially early Cretaceous is indicated by the distribution and 

 character of the Purbeck Beds and contiguous deposits. The marine Cinder Bed 

 within the Purbeck Beds of Dorset and equivalent horizons elsewhere are considered 

 by Casey to mark a marine incursion from the direction of the North Sea Basin (1963). 

 The sea did not invade southern England again until the early Aptian. It is 

 also important to note that in the Speeton area it is the top of the Kimmeridge 

 Clay which is eroded and that heavy clay sedimentation did not commence again 

 until after the start of the Neocomian. 



The depositional history of the Lower Greensand has been discussed by Casey 

 (1961a ; 499-501). At the end of the tardefurcata Zone (Lower Albian) there occurred 

 the last of a number of minor folding phases which Casey has demonstrated affected 

 sedimentation during the formation of the Lower Greensand. This last phase 

 produced a number of parallel ridges and troughs trending between NW. and SE. to 

 WNW.-ESE. , the axes of which were slightly modified during mammillatum Zone times 

 and again later in loricatus Zone times. These, together with a general subsidence 

 of the whole Basin both in England and France or a rise in sea-level, set the stage for 

 Middle Albian sedimentation. The positions of the axes of the structures are shown 

 diagrammatically in text-fig. 52. 



The Middle Albian sequence under Dover shows a good development of the lyelli 

 Subzone overlain by a nodule bed of lower spathi Subzone age. By Folkestone the 

 lyelli Subzone sediments are greatly reduced in thickness but the overlying dentatus 

 nodule bed is of exactly the same age as at Dover. The rest of the Lower Gault 

 sequence also is thinner at Folkestone, where it rests upon a mammillatum Zone 

 sequence in which all four Subzones are represented. 



At Sandling Junction, the basal Gault rests upon puzosianus Subzone sediments as 

 at Folkestone, but these in turn rest directly on an eroded surface of early tardefurcata 

 Zone sediments. Here, the dentatus nodule bed contains species of Hoplites (H.) 

 transitional between those of the dentatus nodule bed at Folkestone and Dover, and 

 those which occur in the ' upper dentatus-spathi nodule bed ' in the northern Weald. 

 From Sandling to Maidstone, puzosianus Subzone sediments rest upon either tarde- 

 furcata or jacobi Zone Folkestone Beds, and the dentatus nodule bed in the basal Gault 



