Chalk Group Lithostratigraphy: Marlborough Downs/Berkshire Downs/Chilterns - Plenus Marls

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The Plenus Marls are more condensed than in the Southern Region (typically 0.9 - 1.7 m thick; Wood, 1996), but are otherwise similar. However, in the Hitchin area and eastwards, the equivalent of Jefferies' (1963) Bed 3 is so indurated that it resembles the Melbourn Rock, and the brachiopod Ornatothyris becomes a characteristic fossil (Wood, 1996).

Macrofossil Biozonation: M. geslinianum Zone (pars) (Wood, 1996)

Correlation: see Correlation with other parts of the UK


JEFFERIES, R P S.1963. The stratigraphy of the Praeactinocamax plenus Subzone (Turonian) in the Anglo-Paris Basin. Proceedings of the Geologists Association, Vol. 74, 1-33.

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: Plenus Marls (Southern Region), Melbourn Rock