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Llanbedrog Volcanic Group

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Llanbedrog Volcanic Group
Stratigraphic range: Caradoc
Lavas of the Foel Ddu Rhyodacite Formation exposed at Carreg y Defaid, just east of Llanbedrog
TypeGroup
Sub-unitsYoke House Formation, Carneddol Rhyolitic Tuff Formation, Foel Ddu Formation, Penmaen Formation
UnderliesNod Glas Formation
OverliesDwyfach Formation
Lithology
PrimaryTuff
OtherLava, volcaniclastic sediments
Location
Regionnorthwest Wales
CountryWales
Type section
Named forLlanbedrog

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]

Outcrops

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This succession of rocks is exposed around the village of Llanbedrog and in a band stretching northwestwards inland.[2]

Lithology and stratigraphy

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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

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  1. ^ http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=LIG (BGS on-line lexicon of rock units)
  2. ^ British Geological Survey 1:50,000 scale geological map (England & Wales) sheet 134 Pwllheli