The BGS Lexicon of Named Rock Units — Result Details

Garn-Gofen Formation

Computer Code: GAGO Preferred Map Code: Gago
Status Code: Full
Age range: Frasnian Age (DR) — Famennian Age (DA)
Lithological Description: Interbedded sandstones and red-brown mudstones. The sandstones in the basal part are pale grey-green quartzites; those in the upper part are grey-green, soft, friable, richly micaceous and feldspathic.
Definition of Lower Boundary: Erosion surface cut in conglomerates of the Craig-y-cwm Formation, overlain by pale yellow to white micaceous sandstone [Lovell, 1978].
Definition of Upper Boundary: Sharp junction between overlying limestone of the Castell Coch Limestone of the Lower Limestone Shale Group and the topmost sandstones of the Garn-gofen Formation. A thin but persistent conglomerate marks the base of the Castell Coch Limestone.
Thickness: Up to a maximum of 20 m.
Geographical Limits: From Blaen Onneu - Daren Cilau area near Crickhowell, Gwent eastwards and southwards to Pontypool, Gwent, South Wales.
Parent Unit: Quartz Conglomerate Group (South Wales) (QCG)
Previous Name(s): Sandstones And Marls (-2812)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Exposures at Craig-y-cwm near Garn-gofen Farm, about 3 km. south-east of Blaenavon, Gwent. [Barclay, 1989]. 
Reference(s):
Barclay, W J. 1975. Annual report for 1974, p. 26. Institute for Geological Sciences: London. 
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. 
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 Unpublished PhD thesis, University of Bristol. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E232