The BGS Lexicon of Named Rock Units — Result Details
Dolgellau Formation
Computer Code: | DLU | Preferred Map Code: | Dlu |
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Status Code: | Full | ||
Age range: | Merioneth Series (EM) — Merioneth Series (EM) | ||
Lithological Description: | Black to dark grey laminated pyritous mudstones and laminated siltstones, carbonaceous. | ||
Definition of Lower Boundary: | Conformably overlies sandstones of the Ffestiniog Flags Formation with a sharp to gradational contact. | ||
Definition of Upper Boundary: | Conformably and transitionally overlain by sandstones and siltstones of the Dol-Cyn-Afon Formation. At Ogof-Ddu marked by phosphatic sandstones with graptolites. | ||
Thickness: | 35 to 150m | ||
Geographical Limits: | Northern, eastern and southern flanks of the Harlech Dome, Snowdonia. | ||
Parent Unit: | Mawddach Group (MWG) | ||
Previous Name(s): | Dolgellau Member [Obsolete Name and Code: Use DLU]
(-4610)
Cwmhesgen Formation [Obsolete Name And Code: See DYN, DLU] (CHN) Dolgelly Beds [Obsolete Name And Code: Use DLU] (DGB) |
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Alternative Name(s): | none recorded or not applicable | ||
Stratotypes: | |||
Reference Section | Nant Derbyniad Quarry, 8km east of Llan Ffestiniog. Howells, M F and Smith, M. 1997. | ||
Reference Section | Ogof Ddu. 900m east of Criccieth Howells, M F and Smith, M. 1997. | ||
Type Section | Upper Mawddach, near junction with Afon Cwm Hesgen. | ||
Reference(s): | |||
Allen, P M, and Jackson, A A. 1985. Geology of the country around Harlech. Memoir of the British Geological Survey, Sheet 135 with part of Sheet 149 (England and Wales). (London: HMSO.) 112 pp. | |||
Belt, T. 1867. On the "Lingula Flags" or "Ffestiniog Group" of the Dolgelly District. Parts I and II. Gelogical Magazine, Vol. 4, 493-495, 536-543. | |||
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. | |||
Fearnsides, W G. 1905. On the geology of Arenig and Moel Llyfnant. Quarterly Journal of the Geological Society, Vol.61, 608-640. | |||
Pratt, W T, Woodhall, D G and Howells, M F. 1995. Geology of the country around Cadair Idris. Memoir of the British Geological Survey, Sheet 149. (England and Wales). (London: HMSO), 111pp | |||
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. | |||
Allen, P M, Jackson, A A, and Rushton, A W A. 1981. The stratigraphy of the Mawddach Group in the Cambrian succession of North Wales. Proceedings of the Yorkshire Geological Society, Vol. 43, 295-329. | |||
Fearnsides, W G. 1910. The Tremadoc slates and associated rocks of south-east Caernarfonshire. Quarterly Journal of the Geological Society of London, Vol.66, 142-188. | |||
1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
E119 E135 E149 |