The BGS Lexicon of Named Rock Units — Result Details

Penmaen Tuff Formation

Computer Code: PMN Preferred Map Code: Pm
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Basaltic trachyandesite lavas and tuffs and derived sediments.
Definition of Lower Boundary: Overlies mudstones and sandstones of the Dwyfach Formation.
Definition of Upper Boundary: Upward change from andesitic lavas and tuffs into rhyodacitic lavas and tuffs of the Foel Ddu Rhyodacitic Formation.
Thickness: 300m
Geographical Limits: Pwllheli area, northwest Wales.
Parent Unit: Nant Ffrancon Subgroup (NFR)
Previous Name(s): Penmaen Formation (-3618)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Exposures near Pwllheli. 
Reference(s):
Young, T P, Gibbons, W and McCarroll, D. 2002. Geology of the country around Pwllheli. Memoir of the British Geological Survey, Sheet 134 (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E119 E134