The BGS Lexicon of Named Rock Units — Result Details

Chalk Group

Computer Code: CK Preferred Map Code: CK
Status Code: Full
Age range: Cenomanian Age (KE) — Maastrichtian Age (KM)
Lithological Description: Chalk, with or without flint and discrete limestone, marl (calcareous mudstone), sponge, calcarenite, phosphatic, hardground and fossil-rich beds.
Definition of Lower Boundary: The lower boundary is generally unconformable (at a burrowed surface) on the underlying Lower Cretaceous strata (Upper Greensand and Gault Formations in the Southern Province and on the Hunstanton Formation in the Northern Province). Oversteps onto older strata in limited basin marginal situations.
Definition of Upper Boundary: The upper boundary is unconformable beneath the Palaeogene or Quaternary basal unconformity onshore in the UK. Conformable beneath Danian age Maureen Formation in parts of the North Sea. Elsewhere offshore the contact is unconformable.
Thickness: The thickness of the whole group is variable depending on the 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 560m of strata are preserved; the most chronostratigraphically complete succession is in Norfolk but this is thought to be only some 400m thick; within the Northern Province up to 530m are preserved but the thickest succession is within the North Sea area where about 1000 to 1300m are preserved.
Geographical Limits: The group is known throughout the onshore outcrops in England (Yorkshire to Kent, Sussex and Dorset), and offshore in the Southern, Central and Northern North Sea areas.
Parent Unit: Not Applicable (-)
Previous Name(s): The Chalk (-2700)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  With the exception of well sections in the North Sea there is no single expanded and entire sequence known for the whole group. The group is divided onshore into provincial areas (Southern, Transitional and Northern). The most complete onshore exposure is in, the near vertically inclined, cliff sections on the Isle of Wight where, under favourable conditions, the greater part of the known Southern Province sequence can be seen. The sea-cliffs of Sussex and Kent afford many of the individual formation stratotype sections for the Southern Province, whilst the sea-cliffs and extensive inland exposures in Yorkshire and Lincolnshire provide the stratotypes for the constituent Northern Province formations. The Transitional Province is represented in the Chiltern Hills and their extension northward to the coast at Hunstanton and widely spaced inliers within the Quaternary cover of East Anglia.  
Reference(s):
Johnson, H and Lott, G K. 1993. 2. Cretaceous of the Central and Northern North Sea. In Knox, R W O'B and Cordey, W G (eds.) Lithostratigraphic nomenclature of the UK North Sea. British Geological Survey, Nottingham. 
Rhys, G H. 1974. A proposed standard lithostratigraphic nomenclature for the southern North Sea and an outline structural nomenclature for the whole of the (UK) North Sea. Report of the Institute of Geological Sciences, 74/8. 
Jukes-Browne, A J and Hill, W. 1903 The Cretaceous Rocks of Britain, Vol.2. The Lower and Middle Chalk of England. Memoir of the Geological Survey of Great Britain. 
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. 
Jukes-Browne, A J and Hill, W. 1904. The Cretaceous Rocks of Britain, Vol.3. The Upper Chalk of England. Memoir of the Geological Survey of Great Britain. 
Rawson, P F, Allen, P M and Gale, A. 2001. A revised lithostratigraphy for the Chalk Group. Geoscientist, Vol.11, p.21. 
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.) 
Lott, G K and Knox, R W O'B. 1994. 7. Post-Triassic of the Southern North Sea. In: Knox, R W O'B and Cordey, W G (eds.) Lithostratigraphic nomenclature of the UK North Sea. British Geological Survey, Nottingham. 
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.) 
Rawson, P F. 1992. Cretaceous, 355-388 in Duff, P McL D and Smith, A J (editors), Geology of England and Wales. (London: 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 102pp. ISBN 0 852725175 
Wood, C J and Smith, E G. 1978. Lithostratigraphical classification of the Chalk in North Yorkshire, Humberside and Lincolnshire. Proceedings of the Yorkshire Geological Society, Vol. 42, 263-287. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E103 E162 E174 E176 E187 E208 E225 E237 E256 E257 E311 E326 E340 E064 E072 E073