The sequence boundary is marked by an increase in clay content and reduction in bed thickness at the top of the M. dixoni Zone (Robaszynski et al., 1998). In basinal areas, such as Folkestone, a shelf margin wedge overlies the sequence boundary, and contains the second of three widely developed acmes of the brachiopod Orbirhynchia mantelliana (Robaszynski et al., 1998). In more proximal areas, the shelf margin wedge is absent, and the sequence boundary is strongly erosive, and equates with the sub-Totternhoe Stone erosion surface. At Folkestone, the transgressive systems tract is represented by the Cast Bed (base of coiuplet 'C1' of Gale, 1995) (Gale et al., 1999), and in more proximal areas by the Totternhoe Stone. Higher in the succession, there is an upward reduction in marl rhythms, approximating to the junction of the traditional Chalk Marl / Grey Chalk junction, and this is inferred to mark the beginning of the highstand (Robaszynski et al., 1998). According to Gale et al. (1999) the top of the highstand falls in the base of the A. jukesbrownei Zone, although they depict the boundary slightly lower on their Fig. 2.
GALE, A S. 1995. Cyclostratigraphy and correlation of the Cenomanian Stage in Western Europe. In HOUSE, M R & GALE, A S (eds.), Orbital Forcing Timescales and Cyclostratigraphy, Geological Society Special Publication, No. 85, pp. 177-197.
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.
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.