Southern Province Chalk nomenclature - White Chalk Subgroup: Culver Chalk Formation
Name
First proposed in Rawson, Allen and Gale (2001) as part of the agreed standard for the Chalk Group of England. Replaces the mapping member of the same name proposed in Bristow, et al. (1997). The term Culver Chalk Member was used by Mortimore (1987) as part of his Sussex White Chalk Formation.
Type section
Whitecliff Bay [SZ 638 854] on the Isle of Wight.
Primary Reference Section
Scratchell’s Bay [SZ 296 847] on the Isle of Wight; Ballard Point [SZ 048 813] in Dorset.
Formal subdivision
Is divided into the Tarrant Chalk Member and the Spetisbury Chalk Member. Informally includes a number of laterally persistent flint and marl beds named in Mortimore (1986) that can be traced outside Sussex in the Southern and Transitional provinces.
Lithology
Soft white chalk, relatively marl free with flint seams. Flints are generally large and in the upper part tabular.
Definition of upper boundary
Conformable at the Portsdown Marl (Mortimore, 1986).
Definition of lower boundary
Conformable. As defined in Mortimore (1986), the base of the Culver Chalk lies low in the quadrata Zone, at the Castle Hill Marl. Strong 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.
Thickness
65 to 75m and exceptionally 90m but can be significantly less where synsedimentary channelling occurs.
Distribution
Limited to Sussex, Hampshire Wiltshire and Dorset and as widely spaced outliers to the north in the Southern Province. It occurrence and distribution beneath the Quaternary deposits of East Anglia in the Transitional Province is not well known.
Previous names
Culver Chalk Member of Mortimore (1986) and as adopted in Bristow et al. (1997). Includes the Tarrant Chalk and Spetisbury Chalk members.
Parent
White Chalk Subgroup.
Age and biostratigraphy
Upper Cretaceous, Campanian. Gonioteuthis quadrata Zone.
References
Rawson, Allen and Gale (2001); Bristow et al. (1999); Bristow, Mortimore and Wood (1997).
Tarrant Chalk Member
Name
Defined in Bristow, Mortimore and Wood (1997) as a stand-alone member in the Upper Chalk Formation. Modified in Rawson et al. (2001) and herein as a member within the Culver Chalk Formation.
Type section
Old pit at the foot of The Cliff, Tarrant Rushton, (see Barton, 1991).
Whitecliff Bay [SZ 638 854] on the Isle of Wight.
Primary Reference Section
Whitecliff Bay [SZ 638 854] on the Isle of Wight.
Formal subdivision
None herein. Informally includes a number of laterally persistent flint and marl beds named in Mortimore (1986) that can be traced outside Sussex in the Southern and Transitional provinces.
Lithology
Soft white chalk with relatively widely spaced but large flint seams.
Definition of upper boundary
Conformable (but see note below on thickness). Inferred to be at the Whitecliff Flint at the boundary between the Sompting and Whitecliff beds of Mortimore (1986).
Definition of lower boundary
Conformable. As defined Mortimore (1986), the base of the Culver Chalk lies low in the quadrata Zone, at the Castle Hill Marl. Strong 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. Approximately coincident with the Arundel Sponge Beds.
Thickness
35-45 m in Sussex, about 30 m in Dorset, but can be considerably reduced where synsedimentary channelling occurs.
Distribution
Limited to Sussex, Hampshire, Wiltshire and Dorset and as widely spaced outliers to the north in the Southern Province. It occurrence and distribution beneath the Quaternary deposits of East Anglia in the Transitional Province is not well known.
Previous names
None
Parent
Culver Chalk Formation.
Age and biostratigraphy
Upper Cretaceous, Campanian. Gonioteuthis quadrata Zone.
References
Rawson, Allen and Gale (2001); Bristow et al. (1999); Bristow, Mortimore and Wood (1997); Barton (1991).
Spetisbury Chalk Member
Name
Defined in Bristow, Mortimore and Wood (1997) as a stand-alone member in the Upper Chalk Formation. Modified in Rawson et al. (2001) and herein as a member within the Culver Chalk Formation.
Type section
Bushes Pit, Bushes Farm, and 1.25km north north west of Winterborne Zelstone.
Whitecliff Bay [SZ 638 854] on the Isle of Wight.
Primary Reference Section
Whitecliff Bay [SZ 638 854] on the Isle of Wight.
Formal subdivision
None herein. Informally includes a number of laterally persistent flint and marl beds named in Mortimore (1986) that can be traced outside Sussex in the Southern and Transitional provinces.
Lithology
Firm White flint with regular large flint seams, some tabular in lower part and of Zoophycus type in the upper part.
Definition of upper boundary
Conformable at the Portsdown Marl 1in the Farlington Redoubt on Portsdown and at Whitecliff Bay, Isle of Wight.
Definition of lower boundary
Conformable (but see note below on thickness). Inferred to be at the Whitecliff Wispy Marls (at Whitecliff Bay) at the boundary between the Sompting and Whitecliff beds of Mortimore (1986).
Thickness
30m at Whitecliff Bay thought to be as thick as 45m in Dorset and around 35m in Hampshire.
Distribution
Limited to Sussex, Hampshire, Wiltshire and Dorset and as widely spaced outliers to the north of the Pewsey/Kingsclere structure in the Southern Province. It possible occurrence and distribution beneath the Quaternary deposits of East Anglia in the Transitional Province is not well known.
Previous names
None.
Parent
Culver Chalk Formation.
Age and biostratigraphy
Upper Cretaceous, Campanian. Gonioteuthis quadrata Zone.
References
Rawson, Allen and Gale (2001); Bristow et al. (1999; Bristow, Mortimore and Wood J (1997); Barton (1991).