Southern Region Chalk Group Lithostratigraphy: Traditional Classification - Lower Chalk

The Lower Chalk comprises strata from the base of the Chalk Group to the top of a clay-rich horizon named the Plenus Marls, and is entirely flint-free. It is very argillaceous in the lower part, consisting of green, sandy, glauconitic clay known as the Glauconitic Marl, overlain by a dark grey, rhythmically bedded succession of marls and limestones, named the Chalk Marl. The higher part of the succession is massively bedded grey or creamy coloured chalk with thin marl seams, traditionally referred to as the 'Grey Chalk', capped by the Plenus Marls. Rawson et al. (1978) recorded that the Lower Chalk is 20- c.58 m thick in Dorset, and up to 66 m thick in Hampshire, 69 m thick in Sussex and 88 m thick in Kent. Lake et al. (1987) recorded up to 86 m of Lower Chalk in the Lewes district of East Sussex, and 78 m to +90 m were recorded by Young and Lake (1988) in the Brighton and Worthing district, spanning East and West Sussex.

Macrofossil Biozonation: M. mantelli Zone, M. dixoni Zone, C. inerme Zone, A. rhotomagense Zone, A. jukesbrownei Zone, C. guerangeri Zone, M. gelinianum Zone (pars)

Correlation: see Correlation with other Southern Region Chalk Group classifications see Correlation with other UK Chalk Group successions

References

LAKE, R D, YOUNG, B, WOOD, C J & MORTIMORE, R N. 1987. Geology of the country around Lewes. Memoir of the British Geological Survey.

RAWSON, P F, CURRY, D, DILLEY, F C, HANCOCK, J M, KENNEDY, W J, NEALE, J W, WOOD, C J & WORSSAM, B C. 1978. A correlation of the Cretaceous rocks in the British Isles. Geological Society of London, Special Report No. 9, 70 pp..

YOUNG, B & LAKE, R D. 1988. Geology of the country around Brighton and Worthing. Memoir of the British Geological Survey.