The BGS Lexicon of Named Rock Units — Result Details
Cwm Eigiau Formation
Computer Code: | CEI | Preferred Map Code: | CEi |
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Status Code: | Full | ||
Age range: | Soudleyan Substage (OY) — Longvillian Substage (OL) | ||
Lithological Description: | Sandstones with siltstones and silty mudstones, tuffs and tuffites. | ||
Definition of Lower Boundary: | Conformably overlies the rhyolitic ash-flow tuffs of the Capel Curig Volcanic Formation (Llewelyn Volcanic Group) or, where the latter are not present, it overlies mudstones of the Nant Ffrancon Subgroup. | ||
Definition of Upper Boundary: | Overlain by ash-flow tuffs of the Lower Rhyolitic Tuff Formation (Snowdon Volcanic Group) and (on the Lleyn Peninsular) the Allt Fawr Rhyolitic Tuff Formation. | ||
Thickness: | 450 - 1300m | ||
Geographical Limits: | Not yet provided. | ||
Parent Unit: | Ogwen Group (OGW) | ||
Previous Name(s): | Blaen Eidda Member [Obsolete Name And Code: Part Of CEI]
(BEI)
Carn-Y-Parc Formation [Obsolete Name and Code: Use CEI] (-2680) Eidda Formation [Obsolete Name And Code: Use CEI] (EI) Carn Y Parc Formation [Obsolete Name And Code: Use CEI] (CYP) |
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Alternative Name(s): | none recorded or not applicable | ||
Stratotypes: | |||
Reference Section | Pont y Gromlech. Howells et al., 1981. | ||
Type Section | Nantmor Valley, southeast side. Orton, 1988. | ||
Reference Section | Northeast of Capel Curig. | ||
Reference(s): | |||
Howells, M F, Leveridge, B E, Evans, C D R and Nutt, M J C, 1981. Classical areas of British Geology. Dolgarrog. Description of 1:25 000 Sheet SH76. London: HMSO for Institute of Geological Sciences. | |||
British Geological Survey. 1993. Corwen, provisional. England and Wales sheet 120. Solid and drift, 1:50 000 (Southampton: Ordnance Survey for British Geological Survey.) | |||
Rushton, A W A and Howells, M F. 1998. Stratigraphical framework for the Ordovician of Snowdonia and the Lleyn Peninsula. British Geological Survey Research Report, RR/99/08. | |||
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. | |||
Orton, G J. 1988. A spectrum of Middle Ordovician fan deltas and braidplain deltas, North Wales: a consequence of varying fluvial clastic input. 23-49 in Nemac, W and Steel, R J (editors), Fan Deltas: Sedimentology and Tectonic Settings. [Glasgow: Blackie.] | |||
Howells, M F and Smith, M. 1997. Geology of the country around Snowdon. Memoir of the British Geological Survey, Sheet 119 (England and Wales). (London: The Stationery Office). 104pp. | |||
1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
E119 E106 E094 E120 E107 E134 |