The BGS Lexicon of Named Rock Units — Result Details
Holywell Nodular Chalk Formation
| Computer Code: | HCK | Preferred Map Code: | HCk |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Cenomanian Age (KE) — Turonian Age (KT) | ||
| Lithological Description: | Generally hard nodular chalks with thin flaser marls and significant proportions of shell debris in part. Base marked by the interbedded coloured marl and chalk succession characteristic of the Plenus Marls Member (a term applicable in both the Southern and Northern Provinces). The Melbourn Rock Member above the base can be distinguished by its lack of shell material. | ||
| Definition of Lower Boundary: | The lower boundary is conformable with the base of the formation taken at the bedding plane immediately below the lower marl bed in the Plenus Marls Member. (Note that the Plenus Marls Member is now considered as part of this formation thus providing a consistent datum throughout the Chalk Group of England and the North Sea). | ||
| Definition of Upper Boundary: | The upper boundary is conformable and is taken at the base of the Gun Gardens Main Marl in the expanded sequences of the Southern Province and at the highest shell detrital bed in mapping terms. | ||
| Thickness: | In thicker successions this formation is generally 25 to 35 m thick. It thins rapidly into the "Transitional" Province of the North Downs, Berkshire Downs and the Chilterns (10 to 15 m) and is almost absent in the southwest of Dorset and in Devon. | ||
| Geographical Limits: | Known throughout the Southern Province, within the Chilterns and northward into East Anglia in the Transitional Province. | ||
| Parent Unit: | White Chalk Subgroup (WHCK) | ||
| Previous Name(s): | Shakespeare Cliff Member [Obsolete Name and Code: Use HCK, NPCH]
(-4223)
Lower Holywell Beds [Obsolete Name and Code: Use HCK] (HLHO) Middle Holywell Beds [Obsolete Name and Code: Use HCK] (HMHO) Holywell Nodular Chalk Member [Obsolete Name and Code: Use HCK] (-1589) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Reference Section | Shillingstone Pit. Working quarry on the north side of Shillingstone Hill. About 25 m of the entire formation is exposed in the quarry, See Mortimore et al. (2001, p.143, Figure 3.35) and Bristow (1995). | ||
| Reference Section | Chinor quarry [SU 754 994] in Oxfordshire. 13m of the formation preseved in the quarry 3 face with a correlation to other standard successions that suggests the uppermost preserved chalk is near to the top of the formation. See Mortimore et al. (2001) and Sumbler and Woods (1992). | ||
| Reference Section | Ashwell Quarry, near Biggleswade. The Melbourn Rock was originally defined at Melbourn in Cambridgeshire where the type site is now poorly exposed in a car park beneath a building. A replacement type section is taken at Ashwell Quarry [TL 2687 3945] on the Biggleswade sheet (see Hopson et al., 1996). | ||
| Reference Section | Shakespear Cliff, Kent. "Plenus Marls Formation" and lower part of the "Shakespear Cliff Member" of the "Dover Chalk Formation" (Robinson, 1996). | ||
| Type Section | Cliff section,Eastbourne to Beachy Head, Sussex. Also the type Section of the Holywell Beds of Mortimore (1986). The Melbourn Rock Bed or Beds were defined by Mortimore (1986) at Gun Gardens, Eastbourne. | ||
| Type Section | The Plenus Marls Member type site at Merstham [TQ 295 542] of Jefferies (1963) is now obscured. | ||
| Reference Section | Akers Steps, including Melbourn Rock Bed. Full Succession visible along cliff face path. See Robinson (1986) where the formation is equivalent to the lower part of his Shakespear Cliff Member (Dover Chalk Formation) and a separate underlying Plenus Marl Formation. | ||
| Type Section | Holywell [TV 603 973] section west of Eastbourne, Sussex. The thickest onshore sequence is seen at Eastbourne adjacent to the Holywell Cafe [TV 602 967]. | ||
| Reference(s): | |||
| Mortimore, R N. 1986. Stratigraphy of the Upper Cretaceous White Chalk of Sussex. Proceedings of the Geologists' Association, Vol.97(2), 97-139. | |||
| Waters, C N, Smith, K, Hopson, P M, Wilson, D, Bridge, D M, Carney, J N, Cooper, A H, Crofts, R G, Ellison, R A, Mathers, S J, Moorlock, B S P, Scrivener, R C, McMillan, A A, Ambrose, K, Barclay, W J, and Barron, A J M. 2007. Stratigraphical Chart of the United Kingdom: Southern Britain. British Geological Survey, 1 poster. | |||
| Bristow, C R, Mortimore, R N, and Wood, C J. 1999. "Lithostratigraphy for mapping the chalk in southern England" by Bristow et al. (1997): discussion. Proceedings of the Geologists' Association, Vol. 110, 68-72. | |||
| Hopson, P M. 2005. A stratigraphical framework for the Upper Cretaceous Chalk of England and Scotland, with statements on the Chalk of Northern Ireland and the UK Offshore Sector. British Geological Survey Research Report RR/05/01 102pp. ISBN 0 852725175 | |||
| Bristow, C R. 1991. Geology of Sheet ST80NW and Sheet ST80SW (Turnworth-Milton Abbas, Dorset). British Geological Survey Technical Report WA/92/20. | |||
| Bristow, C R, Mortimore, R N, and Wood C J. 1997. Lithostratigraphy for mapping the Chalk of southern England. Proceedings of the Geologists' Association, Vol. 108(4), 293-315. | |||
| Robinson, N D. 1986. Lithostratigraphy of the Chalk Group of the North Downs, south-east England. Proceedings of the Geologists' Association, Vol.97(2), 141-170. | |||
| Bristow, C R, Barton, C M, Freshney, E C, Wood, C J, Evans, D J, Cox, B M, Ivimey-Cook, H C, and Taylor, R T. 1995. Geology of the country around Shaftesbury. Memoir of the British Geological Survey, Sheet 313 (England and Wales). | |||
| Bristow, C R. 1989. Geology of the East Stour - Shaftesbury district (Dorset) British Geological Survey Technical Report WA/89/58. | |||
| Mortimore, R N, Wood, C J and Gallois, R W, 2001. British Upper Cretaceous Stratigraphy. Geological Conservation Review Series. No. 23. (Peterborough: Joint Nature Conservation Committee.) | |||
| Sumbler, M G and Woods, M A. 1992. The stratigraphy of the Lower and Middle Chalk at Chinnor, Oxfordshire. Proceedings of the Geologists' Association, Vol.103, 111-118. | |||
| Rawson, P F, Allen, P M and Gale, A. 2001. A revised lithostratigraphy for the Chalk Group. Geoscientist, Vol.11, p.21. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E281 E300 E313 E314 E327 E341 E342 E343 | |||