The BGS Lexicon of Named Rock Units — Result Details

Garnedd-Wen Formation

Computer Code: GNWF Preferred Map Code: notEntered
Status Code: Full
Age range: Hirnantian Age (OH) — Hirnantian Age (OH)
Lithological Description: A heterogenous mixture of silty-mudstones, siltstones, fine- to coarse-grained feldspathic and non-feldspathic sandstones, greywackes and conglomerates.
Definition of Lower Boundary: On Foel Crochan (7706 1050) the lower boundary is transitional over 2.65m. Sandy bands (1-2m) thick occur separated by 10-20cm silty-mudstones. The boundary is taken as the base of the first sandstone band.
Definition of Upper Boundary: Not seen, probably transitional.
Thickness: 1000m-3000m south-west to north east.
Geographical Limits: Passes west into Cardigan Bay, and south to the Pennal Fault. Outcrop Garnedd-Wen Formation crosses Sheet 149 diagonally from south-west to north east.
Parent Unit: Abercorris Group (ARO)
Previous Name(s): Garnedd-Wen Beds [Obsolete Name And Code: Use GNWF] (GWB)
Alternative Name(s): none recorded or not applicable
Type Section  South of Corris on Mynydd Braichgoch and Bryn Llwyd, north of the Tyn-Y-Ceunant, Gaewern and Braich-Goch Quarries. 
Pratt, W T, Woodhall, D G and Howells, M F. 1995. Geology of the country around Cadair Idris. Memoir of the British Geological Survey, Sheet 149. (England and Wales). (London: HMSO), 111pp 
Pugh, W J. 1923. The geology of the district around Corris and Aberllefenni, (Merionethshire). Quarterly Journal of the Geological Society, London, Vol.79, 508-541. 
1:50K maps on which the lithostratigraphical unit is found, and map code used: