The BGS Lexicon of Named Rock Units — Result Details

Culver Chalk Formation

Computer Code: CUCK Preferred Map Code: CCk
Status Code: Full
Age range: Campanian Age (KC) — Campanian Age (KC)
Lithological Description: Soft white chalk, relatively marl free, with flint seams. Flints are generally large and, in the upper part, tabular.
Definition of Lower Boundary: The lower boundary is conformable. As defined in Mortimore (1986), the base of the Culver Chalk lies low in the quadrata Zone, at the Castle Hill Marl. Well-developed marls commonly occur for several metres above the Castle Hill Marls, up to and including the Pepper Box Marls, which are now taken as the base.
Definition of Upper Boundary: The upper boundary is conformable at the Portsdown Marl (Mortimore, 1986) of the overlying Portsdown Chalk Formation. This marl separates very soft chalks with large potstone flints and some stylolitic surfaces from soft white chalks with regularly-spaced, well-developed thin marl beds.
Thickness: 65 to 75m and exceptionally 90m but can be significantly less where synsedimentary channelling occurs.
Geographical Limits: Limited to Sussex, Hampshire Wiltshire and Dorset and as widely spaced outliers to the north in the Southern Province. Its occurrence and distribution beneath the Quaternary deposits of East Anglia in the Transitional Province is not well known.
Parent Unit: White Chalk Subgroup (WHCK)
Previous Name(s): Culver Chalk Member (-829)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Ballard Point, Dorset. Full succession visible from boats but with no accessible landing. The succession is part repeated by the Ballard Down Thrust. 
Reference Section  Scratchell's Bay on the Isle of Wight. Provides the most complete succession of the formation within the bay and around the Needles Headland. The bay is only accessible by boat and the headland exposures of the higher parts of the formastion are only accessible at exceptionally low tides. 
Type Section  Whitecliff Bay, eastern Isle of Wight. Mortimore, 1986. Conspicuous grooves picking out the marl horizons may the formation easily identifiable. The succession is limited by the sub-Palaeogene erosion surface. 
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. 
Rawson, P F, Allen, P M and Gale, A. 2001. A revised lithostratigraphy for the Chalk Group. Geoscientist, Vol.11, p.21. 
Bristow, C R, Barton, C M, Freshney, E C, Wood, C J, Evans, D J, Cox, B M and Woods, M A. 1999. The Wincanton district - a concise account of the geology. Memoir of the British Geological Survey, Sheet 297 (England and Wales). 
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, 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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E314