Cenomanian 6/Turonian 1
The sequence boundary is the sub-Plenus Marls erosion surface, corresponding with the junction of the Grey Chalk Subgroup and White Chalk Subgroup (Gale et al., 1999). The lower part of the Plenus Marls (Jefferies' (1963) beds 1-3) is interpreted as a shelf margin wedge, and the erosive contact of Jefferies' (1963) beds 3/4 is a transgressive surface. The transgressive systems tract is represented by the upper part of the Plenus Marls and the overlying Melbourn Rock (Robaszynski et al., 1998), and includes the Cenomanian / Turonian boundary (between Meads Marls 4 and 5) (Gale, 1996). The maximum flooding surface is coincident with Meads Marl 6 (at the top of the Ballard Cliff Member), and marks an upward decrease in nodularity and increase in bed thickness (Gale, 1996). The highstand succession comprises an interval in the lower and middle part of the Holywell Nodular Chalk, and includes the Filograna avita Event of 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.
GALE, A S, HANCOCK, J M & KENNEDY, W J. 1999. Biostratigraphical and sequence correlation of the Cenomanian successions in Mangyshlak (W. Kazakhstan) and Crimea (Ukraine) with those in southern England. Bulletin de l'Institut Royal des Sciences Naturelles de Belgique, 69, 67-86.
JEFFERIES, R P S. 1963. The stratigraphy of the Actinocamax plenus Subzone (Turonian) in the Anglo-Paris Basin. Proceedings of the Geologists Association, Vol. 74, 1-33.
ROBASZYNSKI, F, GALE, A, JUIGNET, P, AMÉDRO, F, HARDENBOL, J. 1998. Sequence stratigraphy in the Upper Cretaceous series of the Anglo-Paris Basin: exemplified by the Cenomanian stage. Society of Economic Paleontologists and Mineralogists, Special Publication No. 60, 363-386.