The BGS Lexicon of Named Rock Units — Result Details
Porth Meudwy Formation
Computer Code: | PMU | Preferred Map Code: | PMu |
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Status Code: | Full | ||
Age range: | Fennian Stage (OF) — Fennian Stage (OF) | ||
Lithological Description: | Coarse-grained turbiditic sandstones interbedded with very coarse matrix-supported conglomerates, the latter representing mass-flow deposits containing boulders up to 1m of phyllitic and schistose mylonites comparable to those of the Llyn Shear Zone. Subordinate mudstone beds. | ||
Definition of Lower Boundary: | Conformable on the siltstones of the Wig Bach Formation, the boundary being taken at the base of the first coarse-grained turbidite sandstone or slumped unit of the Porth Meudwy Formation. | ||
Definition of Upper Boundary: | Conformably overlain by the ferruginous siltstones, sandstones and ironstones of the Trygarn Formation, the boundary being taken at the top of the highest coarse clastic bed. | ||
Thickness: | 25 to 35m | ||
Geographical Limits: | Not yet entered. | ||
Parent Unit: | Nant Ffrancon Subgroup (NFR) | ||
Previous Name(s): | Porth Meudwy Member [Obsolete Name and Code: Use PMU]
(-459)
Porth Meudwy Beds [Obsolete Name and Code: Use PMU] (-1122) |
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Alternative Name(s): | none recorded or not applicable | ||
Stratotypes: | |||
Partial Type Section | North side of Porth Meudwy and along precipitous coastal cliff sections for nearly 2km as far as Bau Ogof-eiral.[SH 1563 2404]. Gibbons, W and McCarroll, D. 1993. | ||
Reference(s): | |||
Gibbons W and McCarroll D. 1993. Geology of the country around Aberdaron, including Bardsey Island. Memoir of the British Geological Survey, Sheet 133 (England and Wales). (London: H.M.S.O.). 88pp. | |||
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. | |||
Beckly, A J, 1988. The Stratigraphy of the Arenig Series in the Aberdaron to Sarn Area, Western Llyn, North Wales. Geological Journal, Vol.23, 321-337. | |||
1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
E133 |