The BGS Lexicon of Named Rock Units — Result Details
Arfon Group
| Computer Code: | ARN | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Neoproterozoic Era (AZ) — Cambrian Period (E) | ||
| Lithological Description: | Welded, felsic ash-flow tuff, volcanogenic conglomeratic sandstone, fine-grained interlaminated tuffite and tuffaceous sediment. | ||
| Definition of Lower Boundary: | Drawn at the base of welded ash-flow tuffs of the Padarn Tuff Formation (base not exposed). (Correlative of Padarn Tuff Formation = Bwlch Gwyn Felsite, Anglesey). | ||
| Definition of Upper Boundary: | Drawn at conformable upward passage from siltstone and sandstone of the Fachwen Formation (east of Aber-Dinlle Fault) or tuff and tuffite of the Bangor Formation (west of Aber-Dinlle Fault) to purple-red siltstone of the Llanberis Slates Formation. | ||
| Thickness: | Almost 4000m - derived from geophysical evidence as base in not exposed. | ||
| Geographical Limits: | Anglesey and Gwynedd, Wales. | ||
| Parent Unit: | Not Applicable (-) | ||
| Previous Name(s): | Arvonian [Obsolete Name And Code: Use ARN]
(A)
Arvonian Formation [Obsolete Name and Code: Use ARN, TWTH] (-4435) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Type Area | The Arvon lowland between the Menai Straits and Snowdonia, Gwynedd, Wales. | ||
| Reference(s): | |||
| Reedman, A J, Leveridge, B E and Evans, R B. 1984. The Arfon Group (Arvonian?) of North Wales. Proceedings of the Geologists' Association, Vol.95, 313-321. | |||
| Greenly, E. 1930. A question of nomenclature. Geological Magazine, Vol.67, 287-288. | |||
| Howells, M F, 1985. Geology of the country around Bangor. Memoir of the British Geological Survey, Sheet 106. (England and Wales). | |||
| Greenly, E. 1944. The Arvonian rocks of Arvon. Quarterly Journal of the Geological Society, London, 100, 269-287. | |||
| Hicks, H, 1878. On some Pre-Cambrian areas in Wales. Geological Magazine (2), Vol.5, 460-461. | |||
| 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. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E106 | |||