Computer Code: |
CV |
Preferred Map Code: |
notEntered |
Status Code: |
Full |
Age range: |
Longvillian Substage (OL)
— Woolstonian Substage (OS) |
Lithological Description: |
[Obsolete: use SV] Ashflow tuffs with slates, siltstones, limestones and hyaloclastites, alternating thin acid tuffs, tuffites, siltstones and mudstones, and ill sorted pyroclastic deposits with argillaceous debris. |
Definition of Lower Boundary: |
Drawn at the base of the Lower Crafnant Volcanic Formation where ashflow tuff conformably rests upon coarse often pebbly greywackes, regularly bedded and commonly crossbedded of the Carneddau Group. |
Definition of Upper Boundary: |
Drawn at the conformable upward passage of ashflow tuffs with slates, siltstones, limestones and hyaloclastites and conformably overlain by black and grey slates and mudstones of the Llan Rhychwyn Slates. |
Thickness: |
Up to 270 metres. |
Geographical Limits: |
Occupying high ground south of the Afon Llugwy, between Clogwyn-Mawr in the west and Llyn-y-Parc in the east. |
Parent Unit: |
none recorded or not applicable
|
Previous Name(s): |
none recorded or not applicable
|
Alternative Name(s): |
none recorded or not applicable
|
Stratotypes: |
Type Area |
Llyn Crafnant district, near Trefriw, Caernarvonshire. |
Reference(s): |
Howells, M F, Francis, E H, Leveridge, B E and Evans, C D R, 1978. Classical areas of British Geology. Capel Curig and Betws-y-Coed. Description of 1:25 000 Sheet SH75. London: HMSO for Institute of Geological Sciences. |
Davies, D A B. 1936. The Ordovician rocks of the Trefriw district (North Wales). Quarterly Journal of the Geological Society. Vol.92, 64-65,70-77. |
1:50K maps on which the lithostratigraphical unit is found, and map code used: |
none recorded or not applicable |