The BGS Lexicon of Named Rock Units — Result Details

Lower Limestone Shale Group [Obsolete Name And Code: Use AVO]

Computer Code: LSH Preferred Map Code: notEntered
Status Code: Index Level
Age range: Courceyan Substage (CF) — Courceyan Substage (CF)
Lithological Description: Dark grey and black shales with interbedded limestones. Limestones are visibly coarse-/fine-grained crinoidal bioclastic, sometimes oolitic rocks.
Definition of Lower Boundary: Drawn at base of shale/limestone sequence where these rocks lie conformably on the Portishead Beds or other rocks of Upper Old Red Sandstone facies. Locally the boundary is transitional.
Definition of Upper Boundary: Conformable upward transition to dark grey Black Rock Limestone (or lateral equivalents). (Crinoidal bioclastic limestones and dolomites).
Thickness: Up to 150m.
Geographical Limits: Southwest England, South Wales, Forest of Dean, and possibly farther eastwards, beneath younger rocks, at least as far as Kent.
Parent Unit: Not Entered (?)
Previous Name(s): Lower Limestone Shales (-2924)
Alternative Name(s): Avon Group
Cefn Bryn Shales
Stratotypes:
Type Area  Clydach Gorge, Clydach Valley, Abergavenny, Wales. 
Type Area  Quarries, near Bristol. 
Type Section  Maesburg Castle railway cutting, 6 km north-north-east of Shepton Mallet. 
Reference(s):
Buckland, W and Conybeare, W D, 1822. Observations on the south-western coal district of England. Transactions of the Geological Society, Vol.1, p.222. 
Vaughan, A, 1905. The palaeontological sequence in the Carboniferous Limestone of the Bristol area. Quarterly Journal of the Geological Society of London, Vol.61, 181-307. 
Sibley, T F and Reynolds, S H, 1937. The Carboniferous Limestone of the Mitchellean area, Gloucestershire. Quarterly Journal of the Geological Society, Vol.93, p.35. 
Dixon, E E L, 1921. The Geology of the South Wales Coalfield, Part XIII , the country around Pembroke and Tenby, being an account of the region comprised in sheets 244 and 245. Memoir of the Geological Survey of Great Britain (HMSO). 
Reynolds, S H, 1921. The lithological succession of the Avonian at Clifton. Quarterly Journal of the Geological Society of London, Vol.77, 213-243. 
Barclay, W J, Jackson, D I, Mitchell, M, Owen, B, Riley, N J, White, D E, Strong, G E and Monkhouse, R A. 1989. Geology of the South Wales Coalfield, Part II, the country around Abergavenny. Memoir of the British Geological Survey. 
Kellaway, G A and Welch, F B A, 1955. The Upper Old Red Sandstone and Lower Carboniferous rocks of the Bristol and the Mendips compared with those of Chepstow and the Forest of Dean. Bulletin of the Geological Survey of Great Britain, No.9, p.1-21. 
George, T N, 1952. Tournasian facies in Britain. Report of the 18th International Geology Congress, Vol.10, p.37. 
Green, G W and Welch F B A, 1965. The geology of the country around Wells and Chedder. Memoir of the Geological Survey of England and Wales, Sheet 280. 
Cave R. 1977. Geology of the Malmesbury District. Memoir of the Geological Survey of Great Britain, Sheet 251 (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E263 E262 E249 E246 E244 E234 E233 E232 E231 E280 E281 E279 E264 E265 E251 E230 E245 E229 E247 E250