The BGS Lexicon of Named Rock Units — Result Details

Allt Fawr Rhyolitic Tuff Formation

Computer Code: AFR Preferred Map Code: ARF
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Rhyolitic ash-flow tuff.
Definition of Lower Boundary: Lies unconformably on sandstones, tuffs and siltstones of Cwm Eigiau Formation and mudstones of the Nant Ffrancon Subgroup.
Definition of Upper Boundary: Underlies siltstones, sandstones and calcareous mudstones of the Dwyfach Formation.
Thickness: 150m
Geographical Limits: Pwllheli area, northwest Wales.
Parent Unit: Upper Lodge Volcanic Group (ULV)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Reference Section  Moel Bronmiod, near Pwllheli. 
Reference Section  Pen-y-gaer, near Pwllheli. 
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: