Chalk Group Lithostratigraphy: East Anglia - Pre Weybourne Chalk

Around Norwich (Wood, 1988), this unit to which Pitchford (1990a) assigned at least 33 m of strata, has five subdivisions (Pre Weybourne₁ to Pre Weybourne₅, in ascending order). In north Norfolk, it is represented by limited exposures at Cley-next-the-Sea [TG 0540 4400] (Pitchford, 1990), and in the lowest c. 5.4 m of the coastal succession eastwards from Weybourne Hope [TG 1100 4370] (Peake & Hancock, 1970). The main characteristics of the Pre Weybourne Chalk are faunal rather than lithological, the bryozoan Volviflustrellaria taverensis and the echinoid Echinocorys ex gr. conica being particularly characteristic of parts of this interval (Wood, 1988). The Pre-Weybourne Chalk equates with the 'Basal Mucronata Zone Chalk' and 'Eaton Chalk' of Peake & Hancock (1970), which they refer to simply as comprising chalk that is firmer, whiter and with more frequent flints than that seen below. The base of the Pre Weybourne Chalk is the base of the B. mucronata Zone, which in the Trunch Borehole [TG 2933 3455] is represented by either a c. 30 mm thick seam of flaser marls at a depth of 194.99 m to 195.02 m or a mineralised chalk horizon at a depth of 209.07 m (Arthurton et al., 1994). There is no record of a lithological marker at the base of the B. mucronata Zone at outcrops in Norfolk. In the coastal succession, Wood (1988) identified Flint X of Peake & Hancock (1970) as marking the top of the Pre Weybourne Chalk, although more recently Pitchford (1990b) has suggested that the top of the Pre Weybourne Chalk be placed at a hardground c. 0.25 m below Flint X.

Macrofossil Biozonation: B. mucronata Zone

Correlation: see Correlation with other UK Chalk Group successions

References

ARTHURTON, R S, BOOTH, S J, MORIGI, A N, ABBOTT, M A W & WOOD, C J. 1994. Geology of the country around Great Yarmouth. Memoir of the British Geological Survey.

PEAKE, N B & HANCOCK, J M. 1970. The Upper Cretaceous of Norfolk [reprinted with corrigenda and addenda] In LARWOOD, G P & FUNNELL, B M (eds.), The Geology of Norfolk. London & Ashford.

PITCHFORD, A J.1990a. A Summary of the stratigraphy of current exposures of Belemnitella mucronata Zone Chalk (Campanian, Upper Cretaceous) in Norfolk. Bulletin of the Geological Society of Norfolk, Vol. 40, 3-24.

PITCHFORD, A J.1990b. A new correlation within the Belemnitella mucronata Zone (Campanian, Upper Cretaceous) in Norfolk. Bulletin of the Geological Society of Norfolk, Vol. 40, 25-32.

WOOD, C J. 1988. The stratigraphy of the Chalk of Norwich. Bulletin of the Geological Society of Norfolk, No. 38, 3- 120.

See: hardground, flint