The BGS Lexicon of Named Rock Units — Result Details

CORNBRASH FORMATION
Computer Code: CB  Status Code: FORMAL, NATIONAL 
Preferred Map Code: Cb 
Age or Age Range: [ JN ] BATHONIAN  to [ JC ] CALLOVIAN 
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: Parent Unit Code:
GREAT OOLITE GROUP  GOG
Previous Name(s): Previous Code(s):
CORN BRASH  CB 
CORNBRASH   
CORNBRASH LIMESTONE MEMBER   
ABBOTSBURY CORNBRASH FORMATION   
Alternative Name(s):
none recorded or not applicable
Stratotypes:
Type Section  Berry Knap (cliff section), 170m long, 2.5km southsoutheast of Abbotsbury, Dorset 
Reference Section  Old L.M.S. Railway Station Quarry, Thrapston, Northants. (see Douglas and Arkell, 1932). 
Reference Section  Shipton-on-Cherwell Cement Works Quarry, 4.4km northnorthwest of Kidlington, Oxfordshire. 
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. 
Smith, W. 1817. Strata identified by organized fossils, Part 3. [London.] 
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. 
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. 
Page, K N. 1989. A stratigraphic revision for the English Lower Callovian. Proceedings of the Geologists' Association, Vol.100, 363-382. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
Map Code Sheet Name
E  127
E  89
E  43
E  342
E  343
E  217
E  80
E  158
E  143
E  171
E  128
E  114
E  115
E  157
E  159
E  102
E  144
E  237
E  327
E  103
E  172
E  189
E  186
E  265
E  201
E  187
E  236
E  251
E  203
E  253
E  235
E  219
E  218
E  204
E  220
E  252
E  202
E  341
E  281

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