The BGS Lexicon of Named Rock Units — Result Details

Oxford Clay Formation

Computer Code: OXC Preferred Map Code: OxC
Status Code: Full
Age range: Callovian Age (JC) — Oxfordian Age (JO)
Lithological Description: Silicate-mudstone, grey, generally smooth to slightly silty, with sporadic beds of argillaceous limestone nodules. Over most of the outcrop (except the Cleveland Basin, where only the upper part is present) it comprises a tripartite succession: lower part (Peterborough Member) silicate-mudstone, mainly brownish-grey, fissile, organic-rich ("bituminous"), with subordinate beds of pale to medium grey, blocky mudstone; middle part (Stewartby Member) silicate-mudstone, mainly pale to medium grey, smooth to slightly silty, blocky, with subordinate beds of silty shell-debris-rich mudstone; upper part (Weymouth Member) mudstone, mainly pale grey, calcareous, smooth, blocky. For more detail see Peterborough, Stewartby and Weymouth members.
Definition of Lower Boundary: Generally a fairly sharp but generally conformable junction with silicate-sandstone or sandy mudstone of the underlying Kellaways Formation or, in the Cleveland Basin, sandstone of the underlying Osgodby Formation, overlain by silicate-mudstone. In thicker, expanded successions (Wessex Basin) arbitary boundary drawn at the top of highest substantial silicate-sandstone or sandy mudstone above which the succession is predominantly silicate-mudstone.
Definition of Upper Boundary: Upward transition from silicate-mudstone to silty mudstone of the overlying West Walton Formation (Oxford to Market Weighton) or sandy mudstones and calcareous sediments (Dorset to Oxford, and Yorkshire, north of Market Weighton) of the Corallian Group. In Market Weighton area, sharp disconformable contact with chalk (Chalk Group, Hunstanton Formation). In the Westbury to Longleat area, Wiltshire, sharp disconformable contact with sandy micaceous mudstone (Cretaceous, Gault Formation).
Thickness: To 185m (perhaps in south Dorest); typically 50 to 70m over much of the East Midlands Shelf.
Geographical Limits: Dorset coast (Weymouth area) to North Yorkshire coast. Extensive in onshore subcrop, though absent above the interior of the London Platform.
Parent Unit: Ancholme Group (AMG)
Previous Name(s): Clunch Clay And Shale (-1749)
Clunch Clay (-1108)
Fen Clay Formation [Part] (-1109)
Forest Clay (-2357)
Fen Clay (-2966)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Oxford area, including brickpits in and around the city of Oxford. All brickpits now largely infilled and exposure is poor. 
Reference Section  BGS Chalgrove Borehole (SU69NE/20). 2.0km eastsoutheast of Chalgrove, near Oxford. Depth 153.88 to 220.94. Manuscript log and core samples, BGS archive. 
Reference(s):
Phillips, W, 1818. A selection of facts from the best authorities, arranged so as to form an outline of the geology of England and Wales. (London: W Phillips). 
Smith, W. 1817. Strata identified by organized fossils, Part 3. [London.] 
Arkell W J, 1933. The Jurassic System in Great Britain [Oxford: Clarendon Press.] 
Gallois, R W and Cox, B M. 1977. The stratigraphy of the Middle and Upper Oxfordian sediments of Fenland. Proceedings of the Geologists' Association, Vol.88, 207-228. 
Cox, B M, Hudson, J D and Martill, D M, 1992. Lithostratigraphic nomenclature of the Oxford Clay (Jurassic). Proceedings of the Geologists' Association, Vol.103, p.343-345. 
Arkell, W J. 1947. The Geology of Oxford. 267pp. [Oxford: Clarendon Press.] 
Gaunt, G D, Fletcher, T P and Wood, C J. 1992. Geology of the country around Kingston upon Hull and Brigg. Memoir of the British Geological Survey, sheets 80 and 89 (England and Wales). 172pp. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E266 E281 E297 E310 E312 E313 E327 E328 E341 E342 E042 E043 E052 E053 E054 E063 E114 E127 E143 E144 E145 E157 E158 E171 E173 E186 E187 E188 E202 E204 E218 E220 E235 E236 E237 E252 E253 E254 E265 E282 E128 E102 E064 E072 E081 E115 E129 E159 E172 E189 E203 E251 E268 E343