The BGS Lexicon of Named Rock Units — Result Details
Ty'r Gawen Mudstone Formation
Computer Code: | TYGN | Preferred Map Code: | notEntered |
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Status Code: | Full | ||
Age range: | Caradoc Series (O4) — Caradoc Series (O4) | ||
Lithological Description: | Predominantly mudstones with subordinate siltstones and sandstones, locally tuffaceous, with a distinctive phosphatic and ooidal ironstone (the Fron Newydd Member) at its base. | ||
Definition of Lower Boundary: | Regionally unconformable on the Allt Lwyd Formation, Offrwm Volcanic Formation and Cregennan Formation, and paraconformable on the Llyn y Gafr Volcanic Formation. Taken at the appearance of ooidal ironstones and phosphatic mudstones above these various formations. Passes laterally into the Pen y gadair Volcanic Formation. | ||
Definition of Upper Boundary: | Overlain by ash-flow tuffs of the Craig Cau Formation and, in the extreme west of its occurrence, by mudstones of the Ceiswyn Formation, although the nature of the latter boundary is problematical. | ||
Thickness: | To 1000m. | ||
Geographical Limits: | Cadair Idris area, North Wales. | ||
Parent Unit: | Ogwen Group (OGW) | ||
Previous Name(s): | Ty'r Gawen Formation [Obsolete Name and Code: Use TYGN]
(-2509)
Llyn-Y-Gadair Mudstones [Obsolete Name and Code: Use TYGN] (-4945) Llyn Cau Mudstones [Obsolete Name and Code: Use TYGN] (-3740) |
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Alternative Name(s): | none recorded or not applicable | ||
Stratotypes: | |||
Partial Type Section | Craig Cwm-llwyd. Pratt, Woodhall and Howells, 1995. | ||
Partial Type Section | Small pits between Llyn y Gadair and Mynydd Moel (for basal Fron Newydd Member). Pratt, Woodhall and Howells, 1995. | ||
Partial Type Section | Exposures around Ty'r Gawen Farm, 2.5km northeast of Llanegryn. Pratt, Woodhall and Howells, 1995. | ||
Partial Type Section | Craig Cau, on the south side of Cadair Idris, North Wales. Pratt, Woodhall and Howells, 1995. | ||
Partial Type Section | Craig-y-llyn, west of Cadair Idris. Pratt, Woodhall and Howells, 1995. | ||
Reference(s): | |||
Cox, A H. 1925. The geology of the Cadair Idris Range, (Merioneth). Quarterly Journal of the Geological Society of London, Vol.81, p.539-592. | |||
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. | |||
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 | |||
Pratt, W T, 1990. Geological notes and local details for part of 1:10 000 Sheet SH60NE. British Geological Survey Technical Report WA/90/40. | |||
Cox, A H, and Wells, A K. 1927. The geology of the Dolgelley district, Merionethshire. Proceedings of the Geologists' Association, Vol.38, 265-318. | |||
Smith, M, Rushton, A W A and Howells, M H. 1995. New litho- and biostratigraphical evidence for a Mid-Ordovician hiatus in southern central Snowdonia, North Wales. Geological Journal, Vol.30, 145-156. | |||
1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
E149 E136 E135 |