The BGS Lexicon of Named Rock Units — Result Details

Craig-Y-Cwm Formation

Computer Code: CRYC Preferred Map Code: Cryc
Status Code: Full
Age range: Frasnian Age (DR) — Famennian Age (DA)
Lithological Description: Mainly quartz pebble conglomerates, with fine-grained quartzitic grey-green sandstones, pebbly sandstones and red-brown mudstones.
Definition of Lower Boundary: Topmost surface of a persistent calcrete, overlain by quartz pebble conglomerate, the latter appearing in the succession for the first time at this level (Lovell, 1978).
Definition of Upper Boundary: Surface cut in quartz pebble conglomerates, overlain by pale yellow to white micaceous sandstone of the Garn-gofen Formation (Lovell, 1978).
Thickness: 5 m. to a maximum of about 12 m.
Geographical Limits: From Blaen Onneu area near Crickhowell, Gwent eastwards and southwards to Pontypool, Gwent, South Wales.
Parent Unit: Quartz Conglomerate Group (South Wales) (QCG)
Previous Name(s): Quartz Pebble Conglomerate (-1463)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Exposures at Craig-y-cwm, about 3 km. south-east of Blaenavon, Gwent, South Wales. [Barclay, 1989]. 
Reference(s):
Lovell, R W W. 1978. The sedimentology and stratigraphy of the Upper Old Red Sandstone and Lower Limestone Shales of the South Wales Coalfield. Unpublished PhD thesis, University of Bristol. 
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. 
Barclay, W J. 1975. Annual report for 1974, p. 26. Institute for Geological Sciences: London. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E232