The BGS Lexicon of Named Rock Units — Result Details

Lower Cornbrash

Computer Code: LCB Preferred Map Code: notEntered
Status Code: Index Level
Age range: Bathonian Age (JN) — Bathonian Age (JN)
Lithological Description: "A high degree of lithological variation is observed ... very pale coloured bioclastic micritic and nodular limestones are characteristic". (Page, 1989). "Pale cream sparsely ooidal and peloidal, locally very shelly or with thin shelly mudstone partings and pseudonodular appearance" (Bristow, 1999).
Definition of Lower Boundary: Generally sharp, disconformable non-sequence: bioclastic limestone resting upon mudstones (and bioclastic ooidal limestones, locally) of Forest Marble Formation (Wessex Basin and south Midlands), 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: Quasi-conformable or non-sequential contact with limestones of the overlying Upper Cornbrash or, where the latter is absent (eg, south Midlands), disconformable contact with mudstone of the succeeding Kellaways Formation.
Thickness: 0 to c.4m; typically c.3m. Absent north of Peterborough.
Geographical Limits: Dorset Coast (Weymouth area) to Oundle-Fotheringay area, just south of Peterborough. Distribution in subcrop uncertain but probably restricted to Wessex and Worcester basins and southern parts of East Midland Shelf; absent over the London Platform.
Parent Unit: Cornbrash Formation (CB)
Previous Name(s): Berry Member (-4750)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  170m-long,cliff section at Berry Knap, 2.5km southsoutheast of Abbotsbury, Dorset. Full sequence exposed, 3.15m thick. Page, 1989; Cox and Sumbler, 2002, p.22. 
Reference Section  Shipton-on-Cherwell Cement Works Quarry, 4.4km northnorthwest of Kidlington, Oxfordshire. Full sequence exposed, 2.7m thick. Page, 1989; Cox and Sumbler, 2002, p.223. 
Reference(s):
Cox, B M, Hopson, P M and Sumbler, M G. 1991. A new record of the Upper Cornbrash near Buckingham. Proceedings of the Geologists' Association, Vol.102, 63-65. 
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. 
Bristow, C R, Barton, C M, Freshney, E C, Wood, C J, Evans, D J, Cox, B M and Woods, M A. 1999. The Wincanton district - a concise account of the geology. Memoir of the British Geological Survey, Sheet 297 (England and Wales). 
Cox, B M and Sumbler, M G. 2002. British Middle Jurassic Stratigraphy. Geological Conservation Review Series No.26. [Peterborough: Joint Nature Conservation Committee.] 
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:
none recorded or not applicable