The BGS Lexicon of Named Rock Units — Result Details
Llyn y Gafr Volcanic Formation
Computer Code: | LYG | Preferred Map Code: | notEntered |
---|---|---|---|
Status Code: | Full | ||
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 Spilitic Group [Obsolete Name and Code: Use LBV, LYG]
(-4147)
Llyn-Y-Gafr Group [Obsolete Name and Code: Use LYG] (-2307) |
||
Alternative Name(s): | Lower Basic Volcanic Group Basic Volcanic Group [Obsolete: use BGL] Lower Basic (Volcanic) Series |
||
Stratotypes: | |||
Type Area | Around Llyn-Y-Gafr, Cadair Idris, Gwynedd. | ||
Reference(s): | |||
Waters, C N, Smith, K, Hopson, P M, Wilson, D, Bridge, D M, Carney, J N, Cooper, A H, Crofts, R G, Ellison, R A, Mathers, S J, Moorlock, B S P, Scrivener, R C, McMillan, A A, Ambrose, K, Barclay, W J, and Barron, A J M. 2007. Stratigraphical Chart of the United Kingdom: Southern Britain. British Geological Survey, 1 poster. | |||
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. 1927. The geology of the Dolgelley district, Merionethshire. Proceedings of the Geologists' Association, Vol.38, 265-318. | |||
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. | |||
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 | |||
1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
E149 E135 |