The BGS Lexicon of Named Rock Units — Result Details

Lower Trigonia Grit Member

Computer Code: LTG Preferred Map Code: notEntered
Status Code: Full
Age range: Bajocian Age (JB) — Bajocian Age (JB)
Lithological Description: Grey speckled with orange brown very shelly and shell-detrital moderately sandy peloid wackestones, packstones and grainstones with thin marl and sand beds, some shelly; some of the peloids are ferruginous ('ironshot'); commonly pebbly at the base, thins and becomes more marly, ironshot and conglomeratic northwards; the fauna includes bivalves (notably trigoniids), brachiopods, corals and the colonial serpulid Sarcinella (See Sumbler, M G, Barron, A J M and Morigi, A N, 2000).
Definition of Lower Boundary: Disconformity: upward change from peloid and ooid limestone (Scottsquar Member) or sand, clay and sandy limestone (Harford Member) where present (both of Birdlip Formation) into limestone as described in lithology. Generally marked by a hardground.
Definition of Upper Boundary: Upward transition from limestone as described in lithology into sandier, more coarsely shell-detrital, less ironshot limestones (Gryphite Grit Member) or hardground overlain by Salperton Formation.
Thickness: Typically 1 to 2m, maximum c.3m: type section (Leckhampton Hill); 1.5m (British Geological Survey files; Cox, B M, and Sumbler, M G. 2002) to 2.2m (Richardson, L, 1906).
Geographical Limits: North and mid-Cotswolds, Gloucestershire: west of Northleach, Cold Aston and Condicote, northeast of Stroud, south of Blockley. Absent between Birdlip and Cirencester. (Barron, A J M, et al, 1997, fig.4).
Parent Unit: Aston Limestone Formation (ASLS)
Previous Name(s): Lower Trigonia Grit (-379)
Alternative Name(s): none recorded or not applicable
Type Area  Mid Cotswolds, Gloucestershire. 
Type Section  Disused quarry, Leckhampton Hill SSSI, Cheltenham, Gloucestershire. Buckman, J, 1893, p.512; 1895, p.410; Richardson, L, 1906, p.188; British Geological Survey files; Cox, B M, and Sumbler, M G. 2002. 
Reference Section  Harford railway cutting SSSI, Gloucestershire. Buckman, J, 1887, p.118; Richardson, L, 1929; Parsons, C F, 1976, bed 3; 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. 
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. 
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. 
Richardson, L, 1906. Half-day excursion to Leckhampton Hill, Cheltenham. Proceedings of the Cotswold Naturalists' Field Club, Vol.15, 182-189. 
Barron, A J M, 1999. Geology of the Naunton area. British Geological Survey Technical Report WA/98/27. 
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. 
Buckman, S S, 1893. The Bajocian of the Sherborne district: its relation to subjacent and superjacent strata. Quarterly Journal of the Geological Society of London. Vol.49, 479-522. 
Parsons, C F, 1976. Ammonite evidence for dating some Inferior Oolite sections in the North Cotswolds. Proceedings of the Geologists' Association, 87, 45-63. 
Sumbler, M G, Barron, A J M and Morigi, A N, 2000. Geology of the Cirencester district. Memoir of the British Geological Survey, Sheet 235 (England and Wales). 
Richardson, L. 1929. The Country around Moreton in Marsh. Memoir of the Geological Survey of Great Britain, Sheet 217 (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.] 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable