The BGS Lexicon of Named Rock Units — Result Details

Blisworth Clay Formation

Computer Code: BWC Preferred Map Code: BwC
Status Code: Full
Age range: Bathonian Age (JN) — Bathonian Age (JN)
Lithological Description: Silicate-mudstone, grey, commonly variegated purplish red, yellow and green, poorly bedded to blocky. Commonly contains fossil rootlets and sideritic ironstone nodules, and locally with impersistant beds and lenses of argillaceous limestone including (mainly in the south) shell fragmental wackestones, packstones and grainstones, and (mainly in the north) sandstone. Mudstone weathers to highly plastic clay.
Definition of Lower Boundary: Sharp but generally more or less conformable contact: limestone of the Blisworth Limestone Formation (or locally, near its northern limit, bluish and greenish grey variably shelly mudstones of the Rutland Formation) overlain by grey or variegated mudstone.
Definition of Upper Boundary: Sharp, generally disconformable contact: grey or variegated mudstone overlain by bioclastic limestone of the Cornbrash Formation or (very locally near its northern limit) by mudstone and sandstone of the Kellaways Formation.
Thickness: 0 to c.10m; typically 2 to 4m throughout most of its range.
Geographical Limits: East Midlands Shelf, from just north of Milton Keynes, northwards to the Humber area where it is (probably) overstepped by the Cornbrash Formation.
Parent Unit: Great Oolite Group (GOG)
Previous Name(s): Blisworth Clay Member (-4507)
Glentham Formation (GLF)
Great Oolite Clay [Obsolete Name And Code: See Blisworth Clay, BWC] (GOC)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Ketton Quarry, 2.6km north of Ketton, Rutland, near Stamford, Lincolnshire. Full sequence exposed, 5.07 m thick. (Hudson and Clements, 2007, pp 254-257). 
Reference Section  M1 Motorway cutting, southsoutheast of Portfields Farm, Newport Pagnell. See Horton and others,1974. 
Type Section  Thrapston Quarry, 1km southsoutheast of Thrapston, Northamptonshire. Formally fully exposed (2.5m thick), now at least partlty obscured. Cox and Sumbler, 2002, 264, Cripps, 1986. 
Type Area  Blisworth, Northamptonshire. See Sharp, 1870; Arkell, 1933 (Nb: name derives from Sharp's description of a quarry near Blisworth, though in fact the unit he described is probably not the Blisworth Clay as currently defined.) 
Reference(s):
Hudson, J D and Clements, R G. 2007. The Middle Jurassic Succession at Ketton, Rutland. Proceedings of the Geologists' Association, Vol 118, 239-264. 
Sumbler, M G. 2003. In Leicestershire and Rutland Geodiversity Action Plan. British Geological Survey Commissioned Research Report CR/04/063N. 
Arkell W J, 1933. The Jurassic System in Great Britain [Oxford: Clarendon Press.] 
Cripps, D W. 1986. A facies analysis of Upper Great Oolite Group in Central and Eastern England. (University of Aston in Birmingham: Unpublished PhD thesis.) 
Sharp, S. 1870. The Oolites of Northamptonshire, Part 1. Quarterly Journal of the Geological Society of London, Vol. 26, 354-391. 
Cox, B M and Sumbler, M G. 2002. British Middle Jurassic Stratigraphy. Geological Conservation Review Series No.26. [Peterborough: Joint Nature Conservation Committee.] 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E114 E103 E102 E115 E127 E128 E143 E144 E157 E158 E159 E171 E172 E186 E187 E188 E202 E203 E204 E217 E220 E089