The basal sequence boundary is formed by the Fognam Farm Hardground in basin marginal areas such as Wiltshire and the Chilterns (Gale, 1996). The formation of the Fognam Farm Hardground was contemporaneous with the formation of a thin shelf margin wedge in basinal areas, representing the interval between Southerham Marl 1 and the Caburn Marl in the lower part of the Lewes Nodular Chalk Formation of Sussex (Gale, 1996). Slightly higher in the sequence, a transgressive systems tract is represented by the Hitchwood Hardground in basin marginal areas, and by the nodular chalk interval between the Bridgwick Marls and Lewes Marl in basinal areas (Gale, 1996). The sequence terminates at the 'Top Rock' in basin marginal areas, and at the Navigation Hardground in basinal areas (Gale, 1996).
GALE, A S. 1996. Turonian correlation and sequence stratigraphy of the Chalk in southern England. In HESSELBO, S P & PARKINSON, D N (eds), Sequence Stratigraphy in British Geology, Geological Society Special Publication, No. 103, pp. 177–195.