The BGS Lexicon of Named Rock Units — Result Details

Corsham Limestone Formation

Computer Code: CSHF Preferred Map Code: notEntered
Status Code: Full
Age range: Bathonian Age (JN) — Bathonian Age (JN)
Lithological Description: Limestone, white or brown, variably ooidal and shell detrital, grainstone, packstone and wackestone textures, medium to thick-bedded, cross-bedded or massive, with in places especially around Bath one or more lenticular or mound-shaped, shell-detrital, shelly, rubbly limestone beds with compound coral masses, notably at the base (Corsham Coral Bed) and at/towards the top ('Bradford Coral Bed'). Where white, cross-bedded ooidal limestone beds are well developed in the Bath area they have been termed the 'Ancliff Oolite'. The ooidal limestone beds in the lower part in the Sherston area may be sandy. The formation has a rich fauna dominated by brachiopods and bivalves.
Definition of Lower Boundary: Sharp non-sequential change up from white, yellow or light grey ooidal grainstone limestone of the Chalfield Oolite or Athelstan Oolite formations, capped with a hardground that is commonly bored, overlain by ooidal and shell detrital limestone with coralliferous lenses of Corsham Limestone Formation.
Definition of Upper Boundary: Sharp, disconformable change up from ooidal and shell detrital limestone with coralliferous lenses of Corsham Limestone Formation into grey to brown variably sandy medium to coarsely bioclastic grainstone or packstone limestone of Forest Marble Formation; commonly marked by an oyster-encrusted hardground.
Thickness: Lenticular. Up to about 9 m. 6.2 to 6.7 m thick in type section, Corsham railway cutting.
Geographical Limits: Mid and south Cotswolds: from the Tetbury area, Gloucestershire [ST 89 93], where the formation pinches out or passes northwards into the Signet Member of the White Limestone Formation, south to Baggridge [ST 74 56] near Norton St Philip, Somerset where it passes south into the basal beds (Boueti Bed) of the Forest Marble Formation.
Parent Unit: Great Oolite Group (GOG)
Previous Name(s): Corsham Member (-5005)
Great Oolite Of Malmesbury District (-5006)
Upper Rags (-5007)
Upper Rags Member (-5008)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Corsham railway cutting, Corsham, Wiltshire exposing the full thickness of the formation, between 6.2 and 6.7 m thick, overlying the Bath Oolite Member of the Chalfield Oolite Formation, and overlain by the Forest Marble Formation (Barron et al., 2011; Cox and Sumbler, 2002, pp.128-130; Green and Donovan, 1969, pp.50-52, beds 3 to 6). 
Reference Section  Chalfield No.1A Borehole (ST86SE 3) [ST 8523 6333], full thickness at 20.60 to 28.73 m depth. Samples held by BGS. 
Reference Section  Mural exposures at Brown's Folly [ST 795 663 to 794 692], Bathford, formation fully exposed showing 6.4 m of strata including the Bradford Coral Bed and Corsham Coral Bed; underlain by Bath Oolite Member of Chalfield Oolite Formation; overlain by Forest Marble Formation (Cox and Sumbler, 2002, pp.125-127). 
Reference(s):
British Geological Survey. 1970. Malmesbury. England and Wales Sheet 251. Solid and Drift. 1:63 360 Geology Series. (Keyworth, Nottingham: British Geological Survey.) 
Barron, A J M, Lott, G K, and Riding, J B. 2012. Stratigraphical framework for the Middle Jurassic strata of Great Britain and the adjoining continental shelf. British Geological Survey Research Report RR/11/06. 
Cox, B M and Sumbler, M G. 2002. British Middle Jurassic Stratigraphy. Geological Conservation Review Series No.26. [Peterborough: Joint Nature Conservation Committee.] 
Green, G W and Donovan, D T. 1969. The Great Oolite of the Bath area. Bulletin of the Geological Survey of Great Britain, Vol.30, 1-63. 
Sumbler, M G. 2003. Comments on Wyatt and Cave's 'The Chalfield Oolite Formation (Bathonian, Middle Jurassic) and the Forest Marble overstep in the South Cotswolds and the stratigraphical position of the Fairford Coral Bed'. Proceedings of the Geologists' Association, Vol.114, 181-184. 
Lonsdale, W. 1832. On the oolitic district of Bath. Transactions of the Geological Society of London, Series 2, Vol.3, 241-276. 
Barron, A J M, Sheppard, T H, Gallois, R W, Hobbs, P R N, and Smith, N J P. 2011. Geology of the Bath district. British Geological Survey Sheet Explanation, Sheet 265 (England and Wales). 
Cave R. 1977. Geology of the Malmesbury District. Memoir of the Geological Survey of Great Britain, Sheet 251 (England and Wales). 
Wyatt, R J. 1996. A correlation of the Bathonian (Middle Jurassic) succession between Bath and Burford, and its relation to that near Oxford. Proceedings of the Geologists' Association, Vol. 107, 299-322. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable