The BGS Lexicon of Named Rock Units — Result Details

Pen Y Bedw Tuff Member

Computer Code: PYBT Preferred Map Code: PYB
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Acid ash-flow tuffs interbedded with silty calcareous mudstone.
Definition of Lower Boundary: Member at top of Llyn Conwy Formation. Basal contact marked by acid ash-flow tuff.
Definition of Upper Boundary: Below mudstones of undivided Nant Ffrancon Group.
Thickness: 75m
Geographical Limits: Northeast flanks of Harlech Dome.
Parent Unit: Aran Fawddwy Formation (AFM)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Pen y Bedw. 
Reference(s):
Howells, M F and Smith, M. 1997. Geology of the country around Snowdon. Memoir of the British Geological Survey, Sheet 119 (England and Wales). (London: The Stationery Office). 104pp. 
Lynas, B D T, 1973. The Cambrian and Ordovician rocks of the Migneint area, North Wales. Journal of the Geological Society, London, Vol.129, 481-503. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E119