| 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 south-west they are generally well sorted medium-grained and massive, rarely cross-bedded; in the north-east 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 north-east into peloidal packstones and wackestones of the Ardley Member (White Limestone Formation), and the lower part passes south-westwards by decrease in ooid content into the Tresham Rock Formation. At Minchinhampton Common, about 0.5m of very shelly calcareous mudstone and brownish coarse-grained ooidal limestone beds ('The Scroff') occur at the base of the formation (Channon, 1950).
High energy shallow carbonate shelf with mobile ooid shoals. |
| 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. At Minchinhampton Common [SO 85 01] very shelly calcareous mudstone (part of 'The Scroff') at the base of the formation rests sharply on ooid limestone of the Minchinhampton Limestone Member (Taynton Limestone Formation). |
| 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 21 m. |
| 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)
|
| Previous Name(s): |
Bath Stone And Lower Rags
(-645)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Reference Section |
Gate Quarry, Minchinhampton Common [SO 856 017]. |
| Type Section |
BGS Charlton (Lower Moor Farm) Borehole (ST98NE2) [ST 9775 8947]. |
| Type Area |
Tresham to Chipping Sodbury, Gloucestershire [ST 800 923 to 776 830]. |
| Reference(s): |
| 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. |
| Cox, B M, and Sumbler, M G. 2002. British Middle Jurassic Stratigraphy. Geological Conservation Review Series No.26. [Peterborough: Joint Nature Conservation Committee.] |
| 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. |
| Cave R. 1977. Geology of the Malmesbury District. Memoir of the Geological Survey of Great Britain, Sheet 251 (England and Wales). |
| Channon, P J. 1950. New and enlarged Jurassic sections in the Cotswolds. Proceedings of the Geologists' Association, Vol. 61, 242-260. |
| 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. |
| 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. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E251
E252
|
