The BGS Lexicon of Named Rock Units — Result Details

Upper Trigonia Grit Member

Computer Code: UTG Preferred Map Code: UTG
Status Code: Full
Age range: Bajocian Age (JB) — Bathonian Age (JN)
Lithological Description: Very hard poorly but thickly bedded grey and brown very shelly shell-detrital and moderately ooidal grainstone and packstone; characteristic fauna includes trigoniid bivalves, commonly as moulds, and brachiopods.
Definition of Lower Boundary: Hardground capping various members of Aston Limestone or Birdlip Limestone formations, or correlative disconformity on Lias Group, overlain by limestone as in lithological description.
Definition of Upper Boundary: Upward change from limestone as in lithological description, to fine- to coarse-grained ooidal, peloidal/pisoidal and shell-detrital packstone to grainstone (Clypeus Grit Member); commonly a non-sequence marked by a hardground.
Thickness: Typically 1 to 2.5m. Type section; 1.05 to 1.2m. Maximum c.5m (Colesbourne area).
Geographical Limits: Cotswolds: north Gloucestershire to east Avon. Absent east of a line Snowshill-Condicote-Southrop (modified after Barron, A J M, et al, 1997, fig.4). Possibly passes southwards into Maes Knoll Conglomerate (Arkell, W J, 1933, p.237-238).
Parent Unit: Salperton Limestone Formation (SALS)
Previous Name(s): Trigonia Grit (-595)
Upper Trigonia Grit (-3109)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  North Cotswolds, Gloucestershire. 
Reference Section  Rolling Bank Quarry, Cleeve Common SSSI, Gloucestershire. Buckman, S S, 1895, 1897; Richardson, L, 1929; Barron, A J M, 1999; Cox, B M, and Sumbler, M G. 2002. For further reference sections see Barron, A J M, et al, 1997. 
Type Section  Notgrove railway cutting SSSI, 1km eastnortheast of Salperton, Gloucestershire. (Bed 5 of Buckman, S S, 1887, section 6 (first cutting west of Notgrove Station)). See also Woodward, H B, 1894, p.133; Barron, A J M, 1998, Locality Q; Cox, B M, and Sumbler, M G. 2002. 
Reference(s):
Buckman, S S, 1897. Deposits of the Bajocian age in the northern Cotswolds: the Cleeve Hill Plateau. Quarterly Journal of the Geological Society of London, Vol.53, 607-629. 
Buckman, S S, 1895. The Bajocian of the mid-Cotswolds. Quarterly Journal of the Geological Society of London, Vol.51, 388-445; 458-462. 
Barron, A J M, Sumbler, M G and Morigi, A N, 1997. A revised lithostratigraphy for the Inferior Oolite Group (Middle Jurassic) of the Cotswolds, England. Proceedings of the Geologists' Association, Vol.108, 269-285. 
Barron, A J M, 1999. Geology of the Bishop's Cleeve area (1:10 000 Sheet SO92NE). British Geological Survey Technical Report WA/99/01. 
Murchison, R I, 1845. 2nd edition revised by Buckman, J and Strickland, H E. The geology of the neighbourhood of Cheltenham. London: Murray. 
Woodward, H B, 1894. The Jurassic Rocks of Britain, Vol.4. The Lower Oolitic Rocks of England (Yorkshire excepted). Memoir of the Geological Survey of the United Kingdom. 
Cox, B M and Sumbler, M G. 2002. British Middle Jurassic Stratigraphy. Geological Conservation Review Series No.26. [Peterborough: Joint Nature Conservation Committee.] 
Wright, T, 1860. On the subdivisions of the Inferior Oolite of the south of England, compared with the equivalent beds of that formation on the Yorkshire coast. Quarterly Journal of the Geological Society of London, 16, 1-48. 
Arkell W J, 1933. The Jurassic System in Great Britain [Oxford: Clarendon Press.] 
Richardson, L. 1929. The Country around Moreton in Marsh. Memoir of the Geological Survey of Great Britain, Sheet 217 (England and Wales). 
Barron, A J M, 1998. Geology of the Hawling area: 1:10 000 Sheet SP02SE. British Geological Survey Technical Report WA/98/26. 
Buckman, S S, 1887. The Inferior ooilte between Andoversford and Bourton-on-the-Water. Proceedings of the Cotteswold Naturalists' Field Club, Vol.9, 108-135. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E235 E252 E217