The BGS Lexicon of Named Rock Units — Result Details
Nod Glas Formation
| Computer Code: | NOG | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Longvillian Substage (OL) — Onnian Substage (ON) | ||
| Lithological Description: | Black, pyritous, graptolitic mudstone. Rusty weathering, soft, very well cleaved and coal-like. | ||
| Definition of Lower Boundary: | As conventionally defined, lower boundary is a conformable transition over 1.5m, from paler, silty mudstones of Ceiswyn Formation (and equivalents), to coal black soft mudstones of Nod Glas Formation. However, elements of Nod Glas lithostratigraphy (anoxic pelagic beds) appear in the underlying Ceiswyn Formation (Craig Hen-gae Member) at least 200-300m below the junction. The Cadnant Shales (=Llanrychwyn Slates) of the Dolgarrog area, considered to be equivalent to the Nod Glas, are likewise up to 400m thick. See also the Supplementary Information Description. | ||
| Definition of Upper Boundary: | Upper boundary is transitional or possibly a non-sequence locally, from coal black mudstones into pale-bluish grey, bioturbated silty, mudstones of the Broad Vein Formation. Transition occurs over less than 2m but is not exposed. | ||
| Thickness: | Generally 20m to 30m, but up to 400m recorded in Cadnant Shales of North Wales. | ||
| Geographical Limits: | Extends discontinuously from the coast of Cardigan Bay in the southwest to the Conwy area in the north. | ||
| Parent Unit: | Ogwen Group (OGW) | ||
| Previous Name(s): | Ddwyryd Shales [Obsolete Name and Code: Use NOG]
(-3587)
Nod Glas [Obsolete Name and Code: Use NOG] (-3588) Cadnant Shale Formation [Obsolete Name and Code: Use NOG] (-2959) Penarwel Shales [Obsolete Name and Code: Use NOG] (-2960) Black Slates Of Dolwyddelan [Obsolete Name And Code: Use NOG] (BSD) Cadnant Shales Formation [Obsolete Name And Code: See NOG] (CDN) Tyn-Y-Glyn Mudstone Formation [Obsolete Name And Code: See NOG] (TYG) Llanrhychwyn Slates [Obsolete Name And Code: Use NOG] (LLR) Cadnant Shales [Obsolete Name and Code: Use NOG] (*318) Llanrychwyn Slates [Obsolete Name and Code: Use NOG] (-1090) Nod Glas Black Shale [Obsolete Name and Code: Use NOG] (-1091) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Type Section | Nant yr Nod stream section on flank of Cae Afon. Stratotype not defined in detail. Pugh, 1928. | ||
| Reference(s): | |||
| Pugh, W J. 1928. The geology of the district around Dinas Mawddwy (Merioneth). Quarterly Journal of the Geological Society of London. Vol.84, 345-381. | |||
| Lockley, M G. 1980. The geology of the Llanuwchllyn to Llanmawddwy area, south Gwynedd, North Wales. Geological Journal, Vol.15, 21-41. | |||
| Mately, C A. 1938. The geology of the country around Pwllheli, Llanbedrog and Madryn, southwest Carnarvonshire. Quarterly Journal of the Geological Society of London, Vol.94. 555-606. | |||
| 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. | |||
| 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. | |||
| Howells M F, Reedman A J and Leveridge B E. 1985. Geology of the country around Bangor: Explanation for 1:50 000 geological sheet 106 (England and Wales). British Geological Survey Sheet Explanation. [London: HMSO.] 34pp. | |||
| Pugh, W J. 1923. The geology of the district around Corris and Aberllefenni, (Merionethshire). Quarterly Journal of the Geological Society, London, Vol.79, 508-541. | |||
| 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. | |||
| 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. | |||
| 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 | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E149 E136 E106 E119 E094 E120 E137 E134 | |||