The BGS Lexicon of Named Rock Units — Result Details

Clifton Down Group [Obsolete: use BO, HBO, PEMB]

Computer Code: CDGP Preferred Map Code: notEntered
Status Code: Index Level
Age range: Chadian Substage (CI) — Holkerian Substage (CQ)
Lithological Description: [Obsolete: use BO, HBO, PEMB] Coarse bioclastic and oolitic facies showing variation,giving way upwards to a calcitic mudstone facies.
Definition of Lower Boundary: Drawn at the base of the Gully Oolite where grey coarse grained oolitic and crinoidal limestone conformably rests upon grey granular oolitic limestone of the Black Rock Group.
Definition of Upper Boundary: Drawn at the conformable upward passage of calcitic mudstones of the Clifton Down Limestone to fossiliferous, massive, grey crinoidal and oolitic bioclastic limestone of the Hotwells Limestone.
Thickness: 400 metres approx.
Geographical Limits: Clifton, Bristol and the area around Wales and Cheddar.
Parent Unit: none recorded or not applicable
Previous Name(s): none recorded or not applicable
Alternative Name(s): Pembroke Limestone Group
Stratotypes:
Type Area  Between the areas of Burrington Combe, Nordrach-on-Mendip-Castle of Comfort. 
Reference(s):
Green, G W and Welch F B A, 1965. The geology of the country around Wells and Chedder. Memoir of the Geological Survey of England and Wales, Sheet 280. 
Kellaway, G A and Welch, F B A. 1955. The Upper Old Red Sandstone and Lower Carboniferous rocks of the Bristol and the Mendips compared with those of Chepstow and the Forest of Dean. Bulletin of the Geological Survey of Great Britain, No.9, p.1-21. 
Waters, C N, Waters, R A, Barclay, W J, and Davies, J R. 2009. Lithostratigraphical framework for Carboniferous successions of Southern Great Britain (Onshore). British Geological Survey Research Report, RR/09/01. 184pp. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E251 E264 E265 E281