Chalk Group Lithostratigraphy: Marlborough Downs/Berkshire Downs/Chilterns - Chalk Rock: Top Hardground Suite

The single most characteristic hardground of the entire Chalk Rock is the Hitch Wood Hardground, occurring throughout the region, and was alone considered to form the Chalk Rock in many historical accounts. (Bromley & Gale, 1982). It is typically highly convoluted, strongly glauconitised and phosphatised, and associated with a pebble bed that preserves a rich mollusc fauna of gastropods, bivalves and ammonites (Bromley & Gale, 1982). This hardground alone forms the Chalk Rock in the far north-east of the region, and represents a condensed deposit formed by Late Turonian transgression, following the regression which formed the Fognam Farm Hardground (Bromley & Gale, 1982; Gale, 1996). The fauna associated with the hardground is sometimes called the Reussianum Fauna, after the characteristically occurring heteromorph ammonite Hyphantoceras reussianum. The Hitch Wood Hardground equates with an interval from beneath the Bridgewick Marls to the Lewes Marl in the lower part of the Lewes Nodular Chalk Member of the Southern Region (Gale, 1996).

Macrofossil Biozonation: top T. lata Zone and lower S. plana Zone.

Correlation: see Correlation with other parts of the UK

References

BROMLEY, R G & GALE, A S. 1982. The lithostratigraphy of the English Chalk Rock. Cretaceous Research, Vol. 3, 273 - 306.

GALE, A S. 1996. Turonian correlation and sequence stratigraphy of the Chalk in southern England. In

HESSELBO, S P & PARKINSON, D N (eds), Sequence Stratigraphy in British Geology, Geological Society Special Publication, No. 103, pp. 177-195.

See: Reussianum Fauna, Lewes Nodular Chalk Member (Southern Region),Turonian, Bridgewick Marls, Lewes Marl