The BGS Lexicon of Named Rock Units — Result Details

Seaford Chalk Formation

Computer Code: SECK Preferred Map Code: SCk
Status Code: Full
Age range: Coniacian Age (KO) — Santonian Age (KS)
Lithological Description: Firm white chalk with conspicuous semi-continuous nodular and tabular flint seams. Hardgrounds and thin marls are known from the lowest beds. Some flint nodules are large to very large.
Definition of Lower Boundary: In Sussex the lower boundary is conformable at the base of Shoreham Marl 2, which marks the change from regularly spaced nodular and grainy chalk beds of the upper Lewes Nodular Chalk Formation to smooth white chalks. This marl is equivalent to the East Cliff Marl 2 in Kent and is also identified at the Anstey Quarry [TL 395 329] south of Royston, in the "Transitional" Province. In the field, this is the most difficult boundary to place precisely as it falls in the sequence where the predominance of interbeds of hard chalk reduces in favour of soft chalk. The most positive criterion is the incoming of abundant thick-shelled inoceramid debris (Platyceramus) in soft chalks, although this might not be applicable everywhere. The presence of a sequence containing carious flints within the low Seaford Chalk and high Lewes Chalk is a helpful field indicator of the boundary. Geomorphologically the formation characteristically forms long, even, dipslope crests.
Definition of Upper Boundary: The upper boundary is conformable at the Buckle Marl 1 in the Sussex succession (Mortimore, 1986). Typically, at upward change from white flinty chalks with no marl seams to less flinty chalk with numerous marl seams (the Newhaven Chalk Member). The incoming of common Zoophycos flints and the presence of the zonal Uintacrinus socialis crinoid at the base of the Newhaven Chalk Formation are useful indicators in the field.
Thickness: Generally in the range 50 to 80 m in the basinal successions of Sussex and Hampshire within the Southern Province. Equivalent beds in Kent are in the range 55 to 60 m. Over considerable areas of Southern England the thickness of this unit is limited by erosion beneath the sub-Palaeogene unconformity.
Geographical Limits: Known throughout the Southern Province, within the Chilterns and northward into East Anglia in the Transitional Province.
Parent Unit: White Chalk Subgroup (WHCK)
Previous Name(s): Seaford Chalk Member [Obsolete Name and Code: Use SECK] (-3665)
Blandford Chalk Member [Obsolete Name and Code: Use SECK, NCK] (BLCH)
Alternative Name(s): Broadstairs Member [Obsolete: use SECK]
Reference Section  The full succession is available in the cliffs around Ballard Point, Dorset. 
Reference Section  A full succession is visible in the Whitecliff Bay section, Isle of Wight. Access difficult a certain states of the tide 
Reference Section  In the cliffs around White Nothe, Dorset. 
Reference Section  Most of the succession is visible in a number of discontinuous sections between Hope Point [TR 379 463] and White Ness [TR 397 710] in Kent. 
Reference Section  The full succession is visible in the cliffs from Light Point, through Birling Gap [TV 553 959] to the Seven Sisters, Sussex 
Type Section  Foreshore and lower cliffs show the basal boundary stratotype and the full type section of formation is visible along the cliff: sea cliffs at Seaford Head; further details in Mortimore (1986). 
Robinson, N D. 1986. Lithostratigraphy of the Chalk Group of the North Downs, south-east England. Proceedings of the Geologists' Association, Vol.97(2), 141-170. 
Bristow, C R, Mortimore, R N and Wood, C J. 1999. "Lithostratigraphy for mapping the chalk in southern England" by Bristow et al. (1997): discussion. Proceedings of the Geologists' Association, Vol.110, 68-72. 
Waters, C N, Smith, K, Hopson, P M, Wilson, D, Bridge, D M, Carney, J N, Cooper, A H, Crofts, R G, Ellison, R A, Mathers, S J, Moorlock, B S P, Scrivener, R C, McMillan, A A, Ambrose, K, Barclay, W J, and Barron, A J M. 2007. Stratigraphical Chart of the United Kingdom: Southern Britain. British Geological Survey, 1 poster. 
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 
Rawson, P F, Allen, P M and Gale, A. 2001. A revised lithostratigraphy for the Chalk Group. Geoscientist, Vol.11, p.21. 
Mortimore, R N. 1986. Stratigraphy of the Upper Cretaceous White Chalk of Sussex. Proceedings of the Geologists' Association, Vol.97(2), 97-139. 
Gale, A S, Wood, C J and Bromley, R G. 1987. The lithostratigraphy and marker bed correlation in the White Chalk (Cenomanian-Campanian) of southern England. Mesozoic Research, Vol.1, 107-118. 
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:
E281 E297 E300 E314 E317 E327 E332 E341 E342 E343