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.
Geographical Limits: Dorset coast (Weymouth area) to Yorkshire coast (Scarborough area); absent over the Market Weighton High. Extensive in onshore subcrop, though absent over the interior of the London Platform.
Parent Unit: Great Oolite Group (GOG)
Previous Name(s): Corn Brash (-753)
Cornbrash (-1414)
Abbotsbury Cornbrash Formation (-2664)
Cornbrash Limestone Member (-2665)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Old L.M.S. Railway Station Quarry, Thrapston, Northants. (see Douglas and Arkell, 1932). 
Type Section  Berry Knap (cliff section), 170m long, 2.5km southsoutheast of Abbotsbury, Dorset Full sequence exposed, 9.35m thick. Page (1989); Cox and Sumbler (2002, p.223). 
Reference Section  Shipton-on-Cherwell Cement Works Quarry, 4.4km northnorthwest of Kidlington, Oxfordshire. Full sequence exposed, up to about 3m. 
Reference(s):
Smith, W. 1817. Strata identified by organized fossils, Part 3. [London.] 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E281 E341 E342 E343 E217 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