The Gault-Lower Greensand Junction Beds in the northern Weald (England) and Wissant (France), and their depositional environment

Abstract

The Gault-Lower Greensand Junction Beds at representative sections from Bentley, Hampshire in the west, to Folkestone in the east, in southern England, and at Wissant on the opposite French coast are described, some in detail for the first time, others revised from earlier accounts. The nature of the deposits reflects the occurrence of periods of sediment deposition followed by intervals of submarine current scour and phosphatic pebble bed formation. This is associated with the basic transgressive change from shallow water conditions of the late Lower Greensand sea ( Leymeriella acuticostata Subzone), to the deeper and less turbulent water environment in which clay-grade sediments of the Gault were able to be deposited over the region of southern England and northern France. The sediments are dated by ammonites and range in age from the Leymeriella regularis Subzone ( Leymeriella tardefurcata Zone), through the Superzone of Douvilleiceras mammillatum (both Lower Albian) into the early Middle Albian Lyelliceras lyelli Subzone ( Hoplites dentatus Zone), but at no single locality is a continuous sediment sequence preserved. The only evidence of tectonic activity is a folding phase at the end of the acuticostata Subzone followed by planation, which separates the sandwave and lagoonal environment of the bulk of the Folkestone Beds and Woburn Sands from that of the relatively flat-bedded Gault-Lower Greensand Junction Beds.