i,j MIDDLE ALBIAN STRATIGRAPHY 



Nonetheless, the outcrop from Aylesbury (Bucks.) to Okeford Fitzpaine (Dorset) 

 shows a section across a basin in which the lyelli Subzone in particular is well devel- 

 oped, and apparently the intermedins Subzone as well. Whether the margin of the 

 Middle Albian depositional area ever reached Palaeozoic rocks in the Welsh 

 borders is unknown. However, it seems more probable that the margin flanked a 

 land area of Jurassic rocks from the nature of the sediments of the Gault in this area 

 (compare the relationship seen in the Ardennes). There is no doubt that a con- 

 siderable volume of clay sediment was carried eastwards into the depositional area 

 throughout Middle Albian times (p. 147) (cf. Jones 1955). 



It has been shown (p. 53) that as one proceeds westwards along the south coast 

 from the Isle of Wight to the Devon border the basal fossiliferous bed and presumably 

 the underlying pebble beds become later in age. In the deeper part of the Wessex 

 Basin in the Isle of Wight, fine grade lyelli Subzone sediments rest upon coarsely- 

 graded marginal mammillatum Zone Carstone. By Lyme Regis, the lowest fossili- 

 ferous sediments are of intermedins Subzone age consisting of very gritty clays, and 

 rest upon a pebble bed which is of uncertain Subzonal age but probably not older than 

 spathi. The evidence indicates marked diachronism of the base of the Middle 

 Albian sediments, and the progressive transgression of the sea westwards across 

 Jurassic sediments particularly during the spathi Subzone. The furthest margin in 

 the extreme west probably followed the eastern boundary of the Mendip Hills and 

 across to the area of what is now the Blackdown Hills. There is no evidence of any 

 Middle Albian sediments in the western half of the English Channel. 



On the northern coast of France, Middle Albian marginal sediments probably 

 flanked the Palaeozoic rocks north of the Cotentin Peninsula. They are certainly 

 present in the Pays de Caux where sediments of the eodentatus and niobe Subzones 

 consist of very coarse pebbly loams with a high clay content. However, the available 

 evidence from the outcrop and boreholes indicates that the land margin was not to 

 the south-west, south, or south-east, and it is necessary to look for a ridge which 

 underwent active erosion during the Middle Albian in the Baie de la Seine. There 

 seems no doubt that the western margin of the Middle Albian Paris Basin was flanked 

 by Jurassic sediments fringing the Armoricain Massif (text-fig. 33). 



In the Artois, the eastern margin of the Middle Albian sea was formed by the 

 Brabant Massif. In the Boulonnais at Cafflers, and in borings in the area of the 

 Franco-Belgian border, Albian sediments rest upon Palaeozoic rocks on the fringe 

 of the Massif. Of particular interest here, especially in connection with the thinning 

 of Middle Albian sediments in the extreme east of Kent, is the marked rise in the 

 Palaeozoic floor in the region of the Ouenoc off-shore from Cap Blanc Nez (p. 83). 



In general, therefore, it is apparent that in England and in France a progressive 

 transgression over earlier Cretaceous and on to wide areas of Jurassic sediments 

 occurred between the eodentatus and niobe Subzones. Whether this continued later 

 into the loricatus and lautus Zones is uncertain because early Upper Albian erosion has 

 removed the evidence. From this definition of the margin of the northern part of 

 the Anglo-Paris Basin, it is now possible to look at the structures within the de- 

 positional area in England. 



