| Computer Code: |
BDT |
Preferred Map Code: |
BDT |
| Status Code: |
Full |
| Age range: |
Caradoc Series (O4)
— Caradoc Series (O4) |
| Lithological Description: |
Rhyolite lava flows with acidic tuffs. |
| Definition of Lower Boundary: |
Overlies mudstones of the Nant Ffrancon Subgroup and locally the Foel Grach Basalt Formation, with which it interdigitates. |
| Definition of Upper Boundary: |
Overlain by Foel Fras Volcanic Complex, and locally by part of the Nant Ffrancon Subgroup. |
| Thickness: |
Up to 195m, thinning to the north and south. |
| Geographical Limits: |
South of Foel Fras, south-west to Nant Peris. |
| Parent Unit: |
Llewelyn Volcanic Group (LLV)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Area |
Braich Tu Du ridge. |
| Reference(s): |
| Howells, M F, Reedman, A J and Campbell, S D G, 1991. Ordovician (Caradoc) marginal basin volcanism in Snowdonia (north-west Wales). (London: HMSO for the British Geological Survey). |
| Howells, M F, Leveridge, B E, Addison, R and Reedman, A J. 1983. The lithostratigraphical division of the Ordovician underlying the Snowdon and Crafnant volcanic groups, North Wales. Report of the Institute of Geological Sciences, No. 83/1. |
| Howells M F, Reedman A J and Leveridge B E. 1985. Geology of the country around Bangor: Explanation for 1:50 000 geological sheet 106 (England and Wales). British Geological Survey Sheet Explanation. [London: HMSO.] 34pp. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E106
|
