| Lithological Description: |
| Silicate-mudstone, greenish grey, variably calcareous and in the south notably sandy, with lenticular typically cross-bedded limestone units that form banks and channel-fills, especially in lower part. A variety of limestone types occur, of which grey, weathering brown and flaggy, variably sandy medium to coarsely bioclastic grainstone or less commonly packstone predominates, especially at the base, which is increasingly ooidal north from Bath (termed the Acton Turville Beds from Biddestone to Didmarton). Other types include fissile sandy limestone, grading to calcareous sandstone, and oyster-limestone. South of the Mendip Hills, a silici-muddy, fossiliferous lime-mudstone (Boueti Bed) lies at the base. Bivalves and brachiopods dominate the fauna, and lignite debris and fish scales and teeth are common, but infauna and signs of bioturbation are rare. The formation consists of interbedded mudstone and limestone in the Weald and English Channel basins, but in St George's Channel Basin it comprises rhythmically bedded mudstone, siltstone and fine sandstone. |
| Definition of Lower Boundary: |
| South Midlands and Cotswold region: base of silicate-mudstone, greenish grey, or limestone, typically grey to brown variably sandy medium to coarsely bioclastic grainstone or packstone, resting with erosive, commonly channelled, disconformity on white to yellow, peloidal, ooidal or lime mud-rich, less silici-muddy limestone of the White Limestone Formation or the Chalfield Oolite Formation, or on a bored and oyster-encrusted hardground surface of the ooidal limestone of the Athelstan Oolite Formation. South of the Mendip Hills: marked by the Boueti Bed, a fossiliferous lime-mudstone, resting non-sequentially on olive-grey bioturbated mudstone of the Frome Clay Formation (formerly Upper Fuller's Earth). |
| Definition of Upper Boundary: |
| Generally mudstone in the upper part of the Formation, overlain sharply and non-sequentially by ooidal shelly wackestone/packstone of the Cornbrash Formation. |
| Thickness: |
| Up to 5m thick in Buckinghamshire, 10 to 30m in Oxfordshire and Gloucestershire, 30 to about 50m in north Dorset, 30 to 75m in south Dorset and the English Channel (Hamblin et al., 1992)(Barton et al., 2008), St George's Channel 242m proved (Tappin et al., 1994) |
| Geographical Limits: |
| Onshore: Buckingham area (where either overstepped by the Cornbrash Formation or passes into the Blisworth Clay Formation) to the Weymouth area, Dorset Coast. Present at depth in the Weald. Offshore: English Channel, Bristol Channel, St George's Channel. |
| Reference(s): |
| Tappin, D R, Chadwick, R A, Jackson, A A, Wingfield, R T R and Smith, N J P. 1994. The geology of Cardigan Bay and the Bristol Channel. British Geological Survey Memoir. |
| Richardson, L. 1933. The Country around Cirencester. Memoir of the Geological Survey of Great Britain, Sheet 235 (England and Wales). |
| Callomon, J H and Cope, J C W. 1995. The Jurassic geology of Dorset. 51-103 in Taylor, P D (Editor), Field Geology of the British Jurassic. (Bath: The Geological Society.) |
| Arkell, W J. 1947. The Geology of Oxford. [Oxford: Clarendon Press.] |
| Cox, B M and Sumbler, M G. 2002. British Middle Jurassic stratigraphy. Geological Conservation Review Series, Vol.26. (Peterborough: Joint Nature Conservation Committee.) |
| Cope, J C W (Editor). 1980. A correlation of Jurassic rocks in the British Isles. Part Two: Middle and Upper Jurassic. Geological Society of London Special Report, No.15. |
| Allen, J R L and Kaye, P. 1963. Sedimentary facies of the Forest Marble (Bathonian) Shipton-on-Cherwell Quarry, Oxfordshire. Geological Magazine, Vol.110, 153-163. |
| McKerrow, W S and Kennedy, W J. 1973. The Oxford district. Geologists' Association Guide No.3. |
| 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. |
| Hamblin, R J O, Crosby, A, Balson, P S, Jones, S M, Chadwick, R A, Penn, I E, and Arthur, M J. 1992. The geology of the English Channel. British Geological Survey Memoir. |
| Woodward, H B. 1894. The Jurassic rocks of Britain. Vol.4. The Lower Oolitic rocks of England (Yorkshire excepted). Memoir of the Geological Survey of the United Kingdom. |
| Sumbler, M G. 1984. The stratigraphy of the Bathonian White Limestone and Forest Marble formations of Oxfordshire. Proceedings of the Geologists' Association, Vol.95, 51-64. |
| Arkell, W J. 1933. The Jurassic System in Great Britain. [Oxford: Clarendon Press.] |
| Holloway, S. 1983. The shell-detrital calcirudites of the Forest Marble Formation (Bathonian) of south-west England. Proceedings of the Geologists' Association, Vol.94, 259-266. |
| Sumbler, M G. 1999. Correlation of the Bathonian (Middle Jurassic) succession in the Minchinhampton-Burford district; a critique of Wyatt (1996). Proceedings of the Geologists' Association, Vol.110(1), 53-64. |
| Barton, C M, Woods, M A, Bristow, C R, Newell, A J, Westhead, R K, Evans, D J, Kirby, G A and Warrington, G. 2008. Geology of south Dorset and south-east Devon and its World Heritage Coast. British Geological Survey Special Memoir. |
| Donovan, D T, and Hemingway, J E. 1963. Europe; Fasc.3a England, Wales and Scotland; Pt.3a X Jurassic. Lexique stratigraphique international. No.1. (Paris, France: Centre national de la recherche scientifique.) |
