The BGS Lexicon of Named Rock Units — Result Details

Tarrant Chalk Member

Computer Code: TACH Preferred Map Code: TCk
Status Code: Full
Age range: Campanian Age (KC) — Campanian Age (KC)
Lithological Description: Soft white chalk with relatively widely spaced but large flint seams.
Definition of Lower Boundary: The lower boundary is conformable. As defined (Mortimore, 1986), the base of the Culver Chalk lies low in the quadrata Zone, at the Castle Hill Marl. Well-developed 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.
Definition of Upper Boundary: The upper bounday is conformable (but see note on thickness). Inferred to be at the Whitecliff Flint at the boundary between the Sompting and Whitecliff beds of Mortimore (1986).
Thickness: 35 to 45m in Sussex, about 30m in Dorset, but can be considerably reduced where synsedimentary channelling occurs.
Geographical Limits: Limited to Sussex, Hampshire, Wiltshire and Dorset and as widely spaced outliers to the north in the Southern Province. Its occurrence and distribution beneath the Quaternary deposits of East Anglia in the Transitional Province is not well known.
Parent Unit: Culver Chalk Formation (CUCK)
Previous Name(s): none recorded or not applicable
Alternative Name(s): Equivalent To The Lower Part Of The Culver Chalk
Stratotypes:
Type Area  Strata well developed along the Tarrant Valley, Dorset. 
Reference Section  Section within the Whitecliff Bay cliffs on the Isle of Wight. The whole of the succession is visible but access difficult except at exceptionally low tides. Access by boat. 
Partial Type Section  Quarry face in old pit at the foot of The Cliff, Tarrant Rushton, ( see Barton, 1992, figure 4). 14m section that starts about 6m above the base of the formation. 
Reference(s):
Bristow, C R, Barton, C M, Freshney, E C, Wood, C J, Evans, D J, Cox, B M, Ivimey-Cook, H C, and Taylor, R T. 1995. Geology of the country around Shaftesbury. Memoir of the British Geological Survey, Sheet 313 (England and Wales). 
Bristow, C R. 1991. Geology of the Tollard Royal-Tarrant Hinton district. British Geological Survey Technical Report, WA/91/20. 
Barton, C M. 1991. Geology of the Blandford Forum district (Dorset). British Geological Survey Technical Report, WA/91/81. 
Gaster, C T. 1944. The stratigraphy of the Chalk of Sussex, Part III. Western area. Arun Gap to the Hampshire boundary, with zonal map. Proceedings of the Geologists' Association, Vol.55, 173-188, 
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. 
Rawson, P F, Allen, P M and Gale, A. 2001. A revised lithostratigraphy for the Chalk Group. Geoscientist, Vol.11, p.21. 
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 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E300 E313 E314 E327 E341 E342 E343