Chalk Group Lithostratigraphy: East Anglia - Sidestrand Chalk Member
Named by Johansen & Surlyk (1990), the member equates with the 'Pre Porosphaera Beds' of Wood (1967) and overlying 'Porosphaera Beds' of Brydone (1906, 1908, 1938), and is exposed in glacially induced anticlines at Sidestrand [TG 255 404]. The member is c. 10-12 m thick, and comprises white, locally nodular chalk with grey lenticular steaks and 15 bands of nodular flint, one of which (Flint S of Peake & Hancock, 1970, fig. 7) comprises huge cylindrical, black nodules (up to 0.3 m thick and c. 1 m in diameter) with chalk filled holes (Johansen & Surlyk, 1990). The Sidestrand Chalk Member has the greatest faunal diversity in the Norfolk Upper Cretaceous (Peake & Hancock, 1970; Whittlesea, 1990), and is especially characterised by abundant specimens of the sponge Porosphaera globularis and large, thick-tested examples of the echinoid Echinocorys belgica. The base of the member is marked by the Overstrand Pyramidata Hardground, and the top is the top of the hardground labelled 'O' in Peake & Hancock (1970, fig. 7). The Campanian / Maastrichtian stage boundary and the junction of the traditional B. mucronata Zone s.l. and B. lanceolata Zone s.l. is marked by the Upper Overstrand Marl, c. 4 m above the base of the Sidestrand Chalk Member (Mortimore et al., 2001).
Macrofossil Biozonation: topmost B. mucronata Zone s.l. and B. lanceolata Zone s.l.
Correlation: see Correlation with other UK Chalk Group successions
References
BRYDONE, R M.1906. Further notes on the stratigraphy and fauna of the Trimingham Chalk. Geological Magazine, Vol. 43, 13-22, 72-78, 124-31, 289-300.
BRYDONE, R M.1908. On the subdivisions of the Chalk at Trimingham (Norfolk). Quarterly Journal of the Geological Society of London, Vol. 64, 401-12.
BRYDONE, R M.1938. On correlation of some of the Norfolk exposures of Chalk with Belemnitella mucronata. (London: Dulau & Co.)
JOHANSEN, M B & SURLYK, F.1990. Brachiopods and the stratigraphy of the Upper Campanian and Lower Maastrichtian Chalk of Norfolk, England. Palaeontology, Vol. 33(4), 823-872.
MORTIMORE, R N, WOOD, C J & GALLOIS, R W. 2001. British Upper Cretaceous Stratigraphy, Geological Conservation Review Series, No. 23, Joint Nature Conservation Committee, Peterborough.
PEAKE, N B & HANCOCK, J M. 1970. The Upper Cretaceous of Norfolk [reprinted with corrigenda and addenda] In LARWOOD, G P & FUNNELL, B M (eds.), The Geology of Norfolk. London & Ashford.
WHITTLESEA, P S. 1990. The Maastrichtian in Norfolk. Bulletin of the Geological Society of Norfolk, Vol. 40, 33-51.
WOOD, C J. 1967. Some new observations on the Maestrichtian Stage in the British Isles. Bulletin of the Geological Survey of Great Britain, Vol. 27, 271-288.
See: Overstrand Pyramidata Hardground