Chalk Group Lithostratigraphy: Marlborough Downs/Berkshire Downs/Chilterns - Upper Chalk
The Upper Chalk, up to 100 m thick, has at its base an indurated, feature-forming limestone called the Chalk Rock; the top is the Palaeogene erosion surface. The lower part of the Upper Chalk comprises a succession of hard, flinty nodular chalk and indurated chalkstone, with beds of marl and hardgrounds. Relatively little is known of the higher part of the Upper Chalk, which comprises massive, soft to firm white chalk with nodular and tabular flints and occasional marl seams (Hopson et al., 1996; Wood, 1996). Locally, the youngest Upper Chalk is richly phosphatic (Wood, 1996). Apart from the Chalk Rock, two other indurated horizons locally occur in the Upper Chalk, these are the Top Rock, overlain higher in the succession by the Clandon Hardground (Wood, 1996).
Macrofossil Biozonation: T. lata Zone (pars), S. plana Zone, M. cortestudinarium Zone, M. coranguinum Zone, U. socialis Zone, M. testudinarius Zone, O. pilula Zone (Wood, 1996)
Correlation: see Correlation with other parts of the UK
WOOD, C. J. 1996. Upper Cretaceous: the Chalk Group. In SUMBLER, M. G., British Regional Geology: London and the Thames Valley. Fourth Edition. (London: HMSO for the British Geological Survey).
See: Chalk Rock, Top Rock, Clandon Hardground, phosphatic chalk, marl, hardground, chalkstone, nodular chalk, flint