The BGS Lexicon of Named Rock Units — Result Details

Lower Crafnant Volcanic Formation

Computer Code: LCV Preferred Map Code: LCV
Status Code: Full
Age range: Longvillian Substage (OL) — Woolstonian Substage (OS)
Lithological Description: Acidic ash-flow tuffs interbedded with siltstone, mudstone, hyaloclastite and thin basaltic tuffs.
Definition of Lower Boundary: On Cwm Eigiau Formation sandstones.
Definition of Upper Boundary: Overlain by mudstones and siltstones at the base of the Middle Crafnant Volcanic Formation.
Thickness: To 100m
Geographical Limits: Widespread in eastern Snowdonia (see Sheet 106).
Parent Unit: Snowdon Volcanic Group (SV)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Capel Curig. 
Reference Section  (Basal contact). Cae-Mawr. 
Reference(s):
Howells, M F, Leveridge, B E and Evans, C D R, 1973. Ordovician ash-flow tuffs in eastern Snowdonia. Report of the Institute of Geological Sciences, No.73/3. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E120 E106