The Llanbedrog Volcanic Group is an Ordovician lithostratigraphic group (a sequence of rock strata) in northwest Wales. The name is derived from the village of Llanbedrog on the Llyn Peninsula where the strata are exposed.[1]
| Llanbedrog Volcanic Group | |
|---|---|
| Stratigraphic range: Caradoc | |
 Lavas of the Foel Ddu Rhyodacite Formation exposed at Carreg y Defaid, just east of Llanbedrog | |
| Type | Group |
| Sub-units | Yoke House Formation, Carneddol Rhyolitic Tuff Formation, Foel Ddu Formation, Penmaen Formation |
| Underlies | Nod Glas Formation |
| Overlies | Dwyfach Formation |
| Lithology | |
| Primary | Tuff |
| Other | Lava, volcaniclastic sediments |
| Location | |
| Region | northwest Wales |
| Country | Wales |
| Type section | |
| Named for | Llanbedrog |
Outcrops edit
This succession of rocks is exposed around the village of Llanbedrog and in a band stretching northwestwards inland.[2]
Lithology and stratigraphy edit
The Group represents an assemblage of both volcanic rocks - lavas, tuffs, breccias - and volcaniclastic sediments - mudstones, siltstones, sandstones and conglomerates. It comprises (in descending order i.e. youngest first) the Yoke House Formation, the Carneddol Rhyolitic Tuff Formation, the Foel Ddu Formation and, at its base, the Penmaen Formation.
References edit
- ^ http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=LIG (BGS on-line lexicon of rock units)
- ^ British Geological Survey 1:50,000 scale geological map (England & Wales) sheet 134 Pwllheli
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