The BGS Lexicon of Named Rock Units — Result Details

Gwna Group

Computer Code: NGW Preferred Map Code: notEntered
Status Code: Pending Upgrade
Age range: Ediacaran Period (AD) — Comley Series (EC)
Lithological Description: Grit, phyllite, quartzite, limestone, jasper, graphitic phyllite, spilitic pillow lavas and tuffs.
Definition of Lower Boundary: Drawn at the base of the Gwna Group where it rests conformably on the Church Bay Tuffs.
Definition of Upper Boundary: Drawn at the conformable upward passage of the Gwna Group to the base of the Fydlyn Group: diabase passing into chlorite epidote schist.
Thickness: Probably several hundred metres.
Geographical Limits: Anglesey, North Wales.
Parent Unit: Monian Supergroup (N)
Previous Name(s): Gwna Melange Formation (A) [Obsolete Name And Code: See NGW] (GWNM)
Gwna Melange Formation (B) [Obsolete Name And Code: See NGW] (NGWM)
Fydlyn Group [Obsolete Name And Code: See NGW] (NFD)
Fydlyn Felsitic Beds [Obsolete Name And Code: See NGW] (NFFF)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Afon Gwna, near Bodorgan station, Anglesey. 
Reference(s):
Gibbons, W and Harris, A L. 1994. A revised correlation of Precambrian rocks in the British Isles. Geological Society of London Special Report, No.22. 
Shackleton, R M. 1975. Precambrian rocks of Wales. 76-83 in A correlation of Precambrian rocks in the British Isles. Harris, A L, and others (editors). Geological Society of London Special Report No. 6. 
Greenly, E. 1919. Geology of Anglesey. Memoir of the Geological Survey, UK. 
Gibbons, W and Ball, M J. 1991. Discussion on Monian Supergroup srtatigraphy in north-west Wales. Journal of the Geological Society, London, Vol. 148, 5-8. 
Horak, J M and Gibbons, W. 2000. Anglesey and the Lleyn Peninsula (Llyn). 145-179 in Carney, J (editor), Precambrian rocks of England and Wales. Geological Consrvation Review Series, 20. [Peterborough: Joint Nature Conservation Committee.] 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable