Chalk Group Lithostratigraphy: East Anglia - Lower Chalk
The Lower Chalk in the southern part of the district, around Cambridge, is similar to that of the Southern Region, comprising rhythmically bedded soft, grey marly chalk and harder, pale-coloured chalk, overlain by firm, massively-bedded, creamey-grey chalk, locally with distinctive curvilinear jointing (White, 1932; Worssam & Taylor, 1969). Northwards there is pronounced attenuation of the succession, and a change to indurated, hard, nodular chalk. In Cambridgeshire, the Lower Chalk is c. 60 m thick, reducing to c. 40 m at Stoke Ferry, Norfolk, and c. 16 m at Hunstanton, in north Norfolk (Chatwin, 1961). The basal part of the Lower Chalk is divided into Cambridge Greensand overlain by Porcellaneous Beds in the southern part of the region, which are replaced by the Paradoxica Bed in north Norfolk (Bristow, 1990; Gallois, 1994). However, the remainder of the Lower Chalk contains a series of marker horizons that are laterally persistent across the entire region, despite the lithological changes, and these are important for correlation at outcrop and in boreholes. In ascending order these markers are the Lower Inoceramus Bed, Upper Inoceramus Bed, Totternhoe Stone, Nettleton Stone and Plenus Marls (Gallois, 1988, Pattison et al., 1993, Bristow, 1990, Gallois, 1994). The top of the Lower Chalk is the junction of the Plenus Marls and the hard, feature-forming Melbourn Rock at the base of the overlying Middle Chalk.
Macrofossil Biozonation: M. mantelli Zone, M. dixoni Zone, C. inerme Zone, A. rhotomagense Zone, A. jukesbrownei Zone, C. guerangeri Zone, M. geslinianum Zone (pars)
Correlation: see Correlation with other UK Chalk Group successions
References
BRISTOW C R. 1990. Geology of the country around Bury St. Edmunds. Memoir of the British Geological Survey.
CHATWIN, C P. 1961. East Anglia and adjacent areas (4th Edn.). British Regional Geology (Her Majesty's Stationery Office, London.)
GALLOIS, R W.1988. Geology of the country around Ely. Br. Geol. Surv. Memoir.
GALLOIS, R W.1994. Geology of the country around King's Lynn and The Wash. Memoir of the British Geological Survey.
PATTISON, J., BERRIDGE, N. G., ALLSOP, J. M. & WILKINSON, I. P. 1993. Geology of the country around Sudbury (Suffolk). Memoir of the British Geological Survey, Sheet 206 (England & Wales).
WHITE, H J O.1932. The Geology of the country near Saffron Walden. Memoir of the Geological Survey England and Wales (Sheet 205).
WORSSAM, B C & TAYLOR, J H. 1969. Geology of the country around Cambridge. Memoir of the British Geological Survey.
See: Cambridge Greensand, Porcellaneous Beds, Paradoxica Bed, Lower Inoceramus Bed, Upper I noceramus Bed, Totternhoe Stone, Nettleton Stone, Plenus Marls