The BGS Lexicon of Named Rock Units — Result Details

Bath Oolite Member

Computer Code: BHO Preferred Map Code: BO
Status Code: Full
Age range: Bathonian Age (JN) — Bathonian Age (JN)
Lithological Description: Calc-ooidal grainstone, predominantly cream, light grey and pale yellow to white medium- to coarse-grained, with very subordinate bioclastic content, in medium to thick beds and conspicuously cross-bedded in parts with sets locally up to 5m thick; burrowing rare. Wyatt and Cave (2002) recognise lower and upper units of very similar gross lithology separated by a bored hardground.
Definition of Lower Boundary: Sharp change up from generally non-ooidal, pisoidal and shelly limestone of Twinhoe Member into ooid-limestone of Bath Oolite Member. Diachronous (younging southwards), with lateral facies passage (Penn and Wyatt, 1979).
Definition of Upper Boundary: A non-sequence, taken above the highest pale coloured generally moderately bioclastic ooid-grainstone, either erosive or marked by a bored and/or oyster-encrusted hardground, overlain by grey or brown variably sandy bioclastic limestone, variously ooidal or shelly, or locally by calcareous silicate-mudstone (all of the Forest Marble Formation) or in places by white or brown variably ooidal and bioclastic limestone with one or more lenticular coralliferous beds of the Corsham Limestone Formation (termed the 'Upper Rags' by Green and Donovan (1969).
Thickness: Up to 15m, 5 to 8.5m through Bath area (Green and Donovan, 1969). 5.92m in Chalfield No. 1A borehole (ST86SE3), 15.1m in Biddestone borehole (ST87SE1).
Geographical Limits: Bath district: at outcrop, from Baggridge, Somerset, and Trowbridge, Wiltshire, where it passes south into mudstone beds of the Frome Clay Formation, north to near Great Badminton, Gloucestershire, where overstepped northwards by Forest Marble Formation. Precise northern limit uncertain. At depth, may extend east into Weald basin (Wyatt, 2011).
Parent Unit: Chalfield Oolite Formation (CFDO)
Previous Name(s): Bath Freestone (-5122)
Bath Oolite (-5065)
Fine Freestones (-5123)
Lower Part Of Upper Rags And Bath Oolite (Undifferentiated) (-5124)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Bath, Somerset. 
Reference Section  Chalfield No.1A borehole (ST86SE3), full thickness of 5.92 m between 28.73 and 34.65 m depth, overlain by Corsham Limestone Formation and underlain by Twinhoe Member. Samples held by BGS. Wyatt and Cave, 2002 
Reference(s):
Smith, W, 1815. A memoir to the map and delineation of the strata of England and Wales, with part of Scotland. (London: J Cary). 
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. 
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). 
Wyatt, R J. 2011. A gamma-ray correlation of boreholes and oil wells in the Bathonian Stage succession (Middle Jurassic) of the Wealden Shelf subcrop. British Geological Survey Open Report, OR/11/048. 
Penn, I E, and Wyatt, R J. 1979. The stratigraphy and correlation of the Bathonian strata in the Bath-Frome area. Institute of Geological Sciences, London, Vol. 78/22, 23-88. 
Wyatt, R J and Cave, R. 2002. 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.113, 139-152. 
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. 
Lonsdale, W. 1832. On the oolitic district of Bath. Transactions of the Geological Society of London, Series 2, Vol.3, 241-276. 
Arkell W J, 1933. The Jurassic System in Great Britain [Oxford: Clarendon Press.] 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E265