The basal sequence boundary is a nodular chalk bed just below the lowest of the Beachy Head Marls in Sussex (Grant et al., 1999). The overlying lowstand systems tract comprises c. 7 m of chalk in Sussex, containing the Beachy Head Marls and Shoreham Marls (Grant et al., 1999). The top of this systems tract is coincident with the top of the Lewes Nodular Chalk Formation, and the upward lithological change to the Seaford Chalk Formation marks a basin wide increase in water depth and the start of a transgressive systems tract. The maximum flooding surface is locally marked in Sussex by a nodular horizon of sponge and inoceramid shell debris, just 0.7 m above Shoreham Marl 2, and this is overlain by a few metres of highstand systems tract deposits (Grant et al., 1999).
GRANT, S F, COE, A L, ARMSTRONG, H A. 1999. Sequence stratigraphy of the Coniacian succession of the Anglo-Paris Basin. Geological Magazine, 136, 17–38.