The BGS Lexicon of Named Rock Units — Result Details

Athelstan Oolite Formation

Computer Code: AOL Preferred Map Code: AO
Status Code: Full
Age range: Bathonian Age (JN) — Bathonian Age (JN)
Lithological Description: Limestone, white to pale yellow, poorly fossiliferous ooid-grainstones and ooidal limestones, in the southwest they are generally well sorted medium-grained and massive, rarely cross-bedded; in the northeast they become more bioclastic, less well sorted fine- to coarse-grained, commonly cross-bedded. Generally capped by bored, encrusted hardground (mapped on sheets 234 (1972 edition) and 251 (1970 edition) as "chinastone" or "Coppice Limestone" (Cave, 1977)). Lateral passage northeast into peloidal packstones and wackestones of the Ardley Member (White Limestone Formation), and the lower part passes southwestwards by decrease in ooid content into the Tresham Rock Formation.
Definition of Lower Boundary: South of Horsley [ST 840 975]; rapid passage up from fine-grained slightly argillaceous limestone with ooidal limestone lenses (Tresham Rock Formation), into massive ooid-limestones. Locally a thin grey mudstone bed may intervene. North of Horsley; sharp change up from grey mainly calcareous mudstone (Fuller's Earth Formation), or where absent, from shell-detrital limestone of the Dodington Ash Rock Member (Fuller's Earth Formation), into massive ooid-limestones.
Definition of Upper Boundary: Bored and oyster encrusted hardground on ooidal limestone, overlain by pale grey, bioclastic ooidal limestones of Chalfield Oolite Formation, or where absent, brown and grey variably ooidal, sandy or muddy bioclastic lime-grainstone/packstone (Forest Marble Formation). Near the formation's southern limit, grey mudstone of the Fuller's Earth Formation intervenes beneath the Chalfield Oolite.
Thickness: About 3 to 21m
Geographical Limits: Outcrop: Old Sodbury to Cirencester area, Gloucestershire, where the Athelstan Oolite passes into the White Limestone Formation (boundary is taken arbitrarily at the western and southern edges of the 1:50 000 sheet 235 (Cirencester). Subcrop: Hullavington, Wiltshire to Sandpool Farm (Somerford Keynes), Gloucestershire (Wyatt, 1996).
Parent Unit: Great Oolite Group (GOG)
Alternative Name(s): none recorded or not applicable
Reference Section  Gate Quarry, Minchinhampton Common. About 5m of ooidal and bioclastic limestone in the lower part of the formation. 
Type Area  Tresham to Chipping Sodbury, Gloucestershire. 
Type Section  BGS Charlton (Lower Moor Farm) borehole, ST98NE/2, full thickness between 37.36 to 58.20m depth. 
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. 
Arkell, W J and Donovan, D T. 1952. The Fuller's Earth of the Cotswolds and its relation to the Great Oolite. Quarterly Journal of the Geological Society of London, Vol.107, 227-253. 
Cave, R. 1977. Geology of the Malmesbury district. Memoir of the British Geological Survey, Sheet 251 (England and Wales). 
Cox, B M and Sumbler, M G. 2002. British Middle Jurassic Stratigraphy. Geological Conservation Review Series. No.26. (Peterborough: Joint Nature Conservation Committee/Chapman and Hall.) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E251 E252