Gwna group

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Reason: Everything is a bit meager. In particular, the description of the lithology is very poor (especially in view of the mass of listed literature): which sedimentary rocks and which magmatites are contained in the unit, and in what geological context they are (and by that I do not mean the landslide, but what was before was)? The fact that the unit is metamorphic belongs in the introduction. Linguistically, that is partly not the yellow of the egg (“the layers come to light ”), and I also have my doubts about the IPA transcription ... - Gretarsson ( discussion ) 23:27, Oct. 4, 2017 (CEST)

Pillow lava at Gwddw Llanddwyn, Anglesey .

The Gwna Group (English: Gwna Group , ɡuna ) is a lithostratigraphic group in North West Wales . It consists of layers of Young Precambrian ( Ediacarium ) to Cambrian ages. The name is derived from the Afon Gwna River near Bodorgan in Anglesey , where there is a clearly visible outcrop. Sometimes the group is also referred to as Gwna Mélange .

Occurrence

The layers are exposed in different parts of Anglesey , along the coast of the Llŷn Peninsula and on Bardsey Island . Most of the time, the banks form impressive cliffs where the stratification can be clearly seen.

Lithology and stratigraphy

Most of the group rests on the Church Bay Tuffs and is covered by the chlorite schists of the Fydlyn Group . She belongs to the Monian Supergroup . It is believed that the group is actually an olisthoplaka, i.e. the result of a gigantic submarine landslide that may have been triggered by tectonic activities about 614 million years ago. In the layers one also finds clasts , fragments of parent rock in various sizes up to sizes of more than a kilometer. The rocks of the group are sediments and sedimentary rocks as well as igneous rocks . The group as a whole has undergone a minor metamorphosis .

Web links

Individual evidence

  1. ↑ http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=NGW (BGS on-line lexicon of rock units)
  2. ^ British Geological Survey 1: 50,000 scale geological map (England & Wales) sheet 133, 134 & Special sheet Anglesey .
  3. ↑ http://mapapps.bgs.ac.uk/geologyofbritain/home.html
  4. ^ MF Howells: British Regional Geology: Wales. Keyworth, Notts, British Geological Survey 2007.

literature

  • W. Gibbons, MJ Ball: Discussion on Monian Supergroup stratigraphy in north-west Wales. In: Journal of the Geological Society , London, Vol. 148, 1991: 5-8.
  • JM Horak, W. Gibbons: Anglesey and the Lleyn Peninsula (Llyn). In: J. Carney (ed.): Precambrian rocks of England and Wales. Geological Conservation Review Series, 20. [Peterborough: Joint Nature Conservation Committee.] 2000.
  • W. Gibbons, AL Harris: A revised correlation of Precambrian rocks in the British Isles. Geological Society of London Special Report, No 22. 1994.
  • RM Shackleton: Precambrian rocks of Wales. In: AL Harris & al .: A correlation of Precambrian rocks in the British Isles. Geological Society of London Special Report No. 6. 1975: 76-83.
  • E. Greenly: Geology of Anglesey. Memoir of the Geological Survey, UK 1919.