The BGS Lexicon of Named Rock Units — Result Details

White Chalk Subgroup
Computer Code: WHCK Preferred Map Code: WhCk
Status Code: Full
Age range: Cenomanian Age (KE) — Maastrichtian Age (KM)
Lithological Description: Chalk with flints. With discrete marl seams, nodular chalk, sponge-rich and flint seams throughout. Typology of flints and incidence of marl seams is important for correlation.
Definition of Lower Boundary: The lower boundary is conformable on the Grey Chalk Subgroup. Placed at the lowest bed in the Plenus Marls Member at the base of the Holywell Nodular Chalk Formation (Southern Province) and at the base of the same member in the Welton Chalk Formation (Northern Province). (Note that the Plenus Marls Member is now considered as part of this subgroup, thus providing a consistent datum throughout the Chalk Group of England and the North Sea).
Definition of Upper Boundary: Unconformable beneath the Palaeogene/Quaternary basal unconformity onshore in the UK. Conformable beneath Danian age Maureen Formation in parts of the North Sea. Elsewhere unconformable.
Thickness: Variable depending on degree of post-Cretaceous erosion and the relative development of its constituent formations. Onshore the thickest development is within the Hampshire/Sussex area of the Southern Province, where up to about 470 to 515m of strata are preserved; the most chronostratigraphically complete succession is in Norfolk but is thought there to be only some 350m thick; within the Northern Province up to 500m are preserved but the thickest succession is within the North Sea area where about 800 to 1100m are preserved.
Geographical Limits: The Subgroup is known throughout the onshore outcrops in England and offshore in the Southern, Central and Northern North Sea areas.
Parent Unit: Chalk Group (CK)
Previous Name(s): Middle And Upper Chalk Undivided (-607)
Sussex White Chalk Formation (Part) (-1271)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  See Comments section. Isle of Wight and the coastal successions of Sussex (Mortimore, 1986) and Kent (Robinson, 1986) in the Southern Province The numerous strato-types for the constituent formations in the Northern Province (Wood and Smith, 1978). 
Reference Section  See Comments section. None defined for the whole subgroup. Full succession visible under favourable conditions in the Isle of Wight and on the Sussex and Kent coast in the Southern Province, where the constituent formations have their type sections. Can be considered as defined by reference to the type sections of the constituent formations in the Northern Province. 
Reference(s):
Rawson, P F. 2006 Cretaceous: sea levels peak as the North Atlantic opens. In Brenchley P J and Rawson, P F (Editors), The Geology of England and Wales. (London:The Geological Society.) 
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. 
Rawson, P F, Allen, P M and Gale, A S. 2001. The Chalk Group: a revised lithostratigraphy. Geoscientist, Vol.11, p.21. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable
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