Category:Southern Province Chalk nomenclature - White Chalk Subgroup

Name

First proposed in Rawson, Allen and Gale (2001) as part of the agreed standard for the Chalk Group of England.

Type 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.

Primary Reference 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).

Formal subdivisions

Divided in the Southern Province into the Holywell Nodular Chalk Formation, New Pit Chalk Formation, Lewes Nodular Chalk Formation, Seaford Chalk Formation, Newhaven Chalk Formation, Culver Chalk Formation and the Portsdown Chalk Formation. In the Northern Province the subgroup comprises the Welton Chalk Formation, Burnham Chalk Formation, Flamborough Chalk Formation and the Rowe Chalk Formation.

Lithology

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 upper boundary

Unconformable beneath Palaeogene/Quaternary basal unconformity onshore in the UK. Conformable beneath Danian age Maureen Formation in parts of the North Sea. Elsewhere unconformable.

Definition of lower boundary

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).

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.

Distribution

The Subgroup is known throughout the onshore outcrops in England and offshore in the Southern, Central and Northern North Sea areas.

Previous names

None directly equivalent, but the Sussex White Chalk Formation (with excludes the lowest Plenus Marls Member) of Mortimore (1986) is the closest match. Includes the Middle Chalk Formation and Upper Chalk Formation of Bristow, Mortimore and Wood (1997).

Parent

Chalk Group.

Age and biostratigraphy

Upper Cretaceous, Cenomanian to Maastrichtian (onshore UK). Metoicoceras geslinianum to Belemnitella mucronata s.l. Zones and into Belemnella spp. Zones where the highest Campanian and Maastrichtian chalks are encountered. Up to basal Danian (Basal Paleocene) in North Sea Basin.

References

Subgroup first defined herein, with the term-only published in Rawson, Allen and Gale (2001).