mobileMenu


The BGS Lexicon of Named Rock Units — Result Details

Cornbrash Formation

Computer Code: CB Preferred Map Code: Cb
Status Code: Full
Age range: Bathonian Age (JN) — Callovian Age (JC)
Lithological Description: Limestone, medium- to fine-grained, predominantly bioclastic wackestone and packstone with sporadic peloids; generally and characteristically intensely bioturbated and consequently poorly bedded, although better bedded, commonly somewhat arenaceous units occur in places, particularly in the upper part. Generally bluish grey when fresh, but weathers to olive or yellowish brown. Thin argillaceous partings or interbeds of calcareous mudstone may occur.
Definition of Lower Boundary: Generally sharp, disconformable non-sequence: bioclastic limestone resting upon mudstone (and bioclastic ooidal limestones, locally) of the Forest Marble Formation (Wessex Basin and south Midlands), or mudstone of the Blisworth Clay Formation (East Midland Shelf east and north) or mudstone with minor sandstone beds of the Scalby Formation (Cleveland Basin).
Definition of Upper Boundary: Base of succeeding Kellaways Formation or Cayton Clay Formation (in the Cleveland Basin); comprising mudstone, commonly shelly at base, resting generally sharply and conformably or non-sequentially on bioclastic limestone of the Cornbrash.
Thickness: 0 to c. 10.5m (Page, 1989); thickest in Wessex Basin but more generally 2 to 4m from Wiltshire to Yorkshire
Geographical Limits: Dorset coast (Weymouth area) to Yorkshire coast (Scarborough area); absent over the Market Weighton High. Extensive in onshore subcrop, including the Weald Basin (Wyatt, 2011), though absent over the interior of the London Platform. Offshore: present in the offshore extensions of the Weald and Wessex basins, in the English Channel (Hamblin et al., 1992), and recognised in the Bristol Channel and St. George’s Channel basins (Tappin et al., 1994).
Parent Unit: Great Oolite Group (GOG)
Previous Name(s): Abbotsbury Cornbrash Formation (-2664)
Cornbrash Limestone Member (-2665)
Corn Brash (-753)
Cornbrash (-1414)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Shipton-on-Cherwell Cement Works Quarry, 4.4km north-north-west of Kidlington, Oxfordshire. Complete Lower Cornbrash Member and basal part of Upper Cornbrash Member exposed at top of quarry, up to about 3m (Cox and Sumbler, 2002). 
Type Section  Berry Knap (cliff section), 170m long, 2.5km south-south-east of Abbotsbury, Dorset. Full sequence exposed, 9.35m thick. Page (1989); Cox and Sumbler (2002, p.223). 
Reference Section  Old L.M.S. Railway Station Quarry, Thrapston, Northants. (see Douglas and Arkell, 1932). 
Reference(s):
Cox, B M, and Sumbler, M G. 2002. British Middle Jurassic Stratigraphy. Geological Conservation Review Series No.26. [Peterborough: Joint Nature Conservation Committee.] 
Wright, J K. 1977. The Cornbrash Formation (Callovian) in North Yorkshire and Cleveland. Proceedings of the Yorkshire Geological Society, Vol.41, 325-346. 
Page, K N. 1989. A stratigraphic revision for the English Lower Callovian. Proceedings of the Geologists' Association, Vol.100, 363-382. 
Douglas, J A and Arkell, W J. 1928. The Stratigraphical Distribution of the Cornbrash: I. The southwestern area. Quarterly Journal of the Geological Society, Vol.84, 117-178. 
Douglas, J A and Arkell, W J. 1932. The Stratigraphical Distribution of the Cornbrash II. The northeastern area. Quarterly Journal of the Geological Society, Vol.88, 112-170. 
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. 
Buckman, S S, 1927. Type Ammonites, Vol.6. (London: S S Buckman) 
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. 
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 United Kingdom Offshore Regional Report. 
Tappin, D R, Chadwick, R A, Jackson, A A, Wingfield, R T R and Smith, N J P. 1994. United Kingdom offshore regional report; the geology of Cardigan Bay and Bristol Channel. (London: HMSO for the British Geological Survey.) 
Hudson, J D. 1962. The stratigraphy of the Great Estuarine Series (Middle Jurassic) of the Inner Hebrides. Transactions of the Edinburgh Geological Society, Vol.19, 135-165. 
Cope, J C W. 2006. Jurassic: the returning seas. The geology of England and Wales. Brenchley, P J, and Rawson, P F (editors). (London: Geological Society.) 
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. 
Smith, W. 1817. Strata identified by organized fossils, Part 3. [London.] 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E080 E089 E127 E158 E043 E327 E102 E237 E103 E114 E115 E128 E143 E144 E157 E159 E171 E203 E172 E186 E187 E189 E201 E202 E204 E218 E220 E235 E236 E251 E252 E253 E265 E219 E281 E341 E342 E343 E217