The BGS Lexicon of Named Rock Units — Result Details

Gwna Melange Formation (A) [Obsolete Name And Code: See NGW]

Computer Code: GWNM Preferred Map Code: GwM
Status Code: Index Level
Age range: Ediacaran Period (AD) — Ediacaran Period (AD)
Lithological Description: The Gwna Melange Formation is an obsolete term, first coined by Shackleton (1975) for the widely recognised late Precambrian olistostrome of Anglesey and Llyn. He considered this major brecciated unit as part of a larger 'Gwna Group' (Shackleton, 1969;1975) that also contained recognisable units ('formations') of coarse sandstones, mudstones ('pelites') and spilitic lavas. Although the name 'Gwna Group' has gained wide acceptance ( Gibbons 1991; 1994; Horak and Gibbons, 2000), Shackleton's stratigraphy has never been adopted, and the term 'Gwna Melange Formation' has fallen into disuse. Its usage is not recommended because of confusion with the currently named Gwna Group. Recommend that the term Gwna Melange Formation is rendered obsolete.
Definition of Lower Boundary: none recorded or not applicable
Definition of Upper Boundary: none recorded or not applicable
Thickness: none recorded or not applicable
Geographical Limits: none recorded or not applicable
Parent Unit: Gwna Group (NGW)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
none recorded or not applicable
Reference(s):
Gibbons W and McCarroll D. 1993. Geology of the country around Aberdaron, including Bardsey Island. Memoir of the British Geological Survey, Sheet 133 (England and Wales). (London: H.M.S.O.). 88pp. 
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. 
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.] 
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. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E133 E094 E134