The BGS Lexicon of Named Rock Units — Result Details
Fachwen Formation
| Computer Code: | FA | Preferred Map Code: | Fa |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Ediacaran Period (AD) — Comley Series (EC) | ||
| Lithological Description: | Conglomerates, sandstones and thin volcanic tuffs at base passing up into siltstones and sandstones. | ||
| Definition of Lower Boundary: | Unconformity on ash-flow tuffs of the Padarn Tuff Formation (Arfon Group). | ||
| Definition of Upper Boundary: | Overlain conformably by mudstones of the Llanberis Slates Formation. | ||
| Thickness: | 40 - 50 m thick. | ||
| Geographical Limits: | Northern Snowdonia. | ||
| Parent Unit: | Harlech Grits Group (HGG) | ||
| Previous Name(s): | Tryfan Grit Group [Obsolete Name and Code: Use FA]
(-4645)
Tryfan Grit Group (A) [Obsolete Name And Code: Use FA] (ACTG) Tryfan Grit Group (B) [Obsolete Name And Code: Use FA] (ACTV) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Type Section | Fachwen. | ||
| Reference(s): | |||
| 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. | |||
| Reedman, A J, Leveridge, B E and Evans, R B. 1984. The Arfon Group (Arvonian?) of North Wales. Proceedings of the Geologists' Association, Vol.95, 313-321. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E119 E106 E118 | |||