The BGS Lexicon of Named Rock Units — Result Details

Llyn Y Gafr Volcanic Formation

Computer Code: LYG Preferred Map Code: notEntered
Status Code: Pending Upgrade
Age range: Llanvirn Series (OE) — Caradoc Series (O4)
Lithological Description: Massive pillowed basalt lavas with reddened tops, and intercalated mafic tuffs with subordinate felsic tuffs and mudstones.
Definition of Lower Boundary: Conformably overlies the dark grey mudstones of the Cregennan Formation (Cefn Hir Member in places). Passes laterally into the Brithion Formation.
Definition of Upper Boundary: Unconformably or disconformably overlain by he Ty'r Gowen Mudstone Formation, commonly represented by an oolitic ironstone (the Fron Newydd Member).
Thickness: To 360m
Geographical Limits: The Cadair Idris District, Gwynedd, North Wales.
Parent Unit: Aran Volcanic Group (AVG)
Previous Name(s): Llyn-Y-Gafr Group (-2307)
Llyn-Y-Gafr Spilitic Group (-4147)
Alternative Name(s): Lower Basic (Volcanic) Group
Basic Volcanic Group
Lower Basic (Volcanic) Series
Stratotypes:
Type Area  Around Llyn-Y-Gafr, Cadair Idris, Gwynedd. 
Reference(s):
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 
Cox, A H and Wells, A K, 1927. The geology of the Dolgelley district, Merionethshire. Proceedings of the Geologists' Association, Vol.38, 265-318. 
Jones, B, 1933. The geology of the Fairbourne-Llwyngwril district, Merioneth. Quarterly Journal of the Geological Society, Vol.89, 145-171. 
Davies, R G, 1959. The Cader Idris Granophyre and its associated rocks. Quarterly Journal of the Geological Society, London. Vol.115, 189-216. 
Williams, A and others, 1972. A correlation of Ordivician rocks in the British Isles. Geological Society of London Special Report No.3. 
Cox, A H and Wells, A K, 1916. The Ordovician sequence in the Cader Idris district (Merioneth). British Association for the Advancement of Science Report for 1915 (Manchester), p.424. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E149 E135