| Computer Code: |
FRT |
Preferred Map Code: |
FRT |
| Status Code: |
Full |
| Age range: |
Soudleyan Substage (OY)
— Soudleyan Substage (OY) |
| Lithological Description: |
Coarse- to fine-grained rhyodacitic lithic tuff and tuffaceous sandstones and siltstones with rare fossils. |
| Definition of Lower Boundary: |
Lithic tuff at base conformably overlies the siltstones of the Glyn Gower Siltstone Member, within the Ceiswyn Formation. |
| Definition of Upper Boundary: |
Tuffaceous sandstones are conformably overlain by mudstones of the Ceiswyn Formation. |
| Thickness: |
2 metres. Lateral variations 0 - 17 metres. |
| Geographical Limits: |
Corwen and Bala districts, North Wales. |
| Parent Unit: |
Ceiswyn Formation (CSW)
|
| Previous Name(s): |
Frondderw Ash [Obsolete Name And Code: See FRT]
(FRA)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Partial Type Section |
Disused quarry, 200m northnorthwest of Frondderw House (now Maes Awelon). Bassett et al, 1966. |
| Reference(s): |
| Campbell, S D G. 1983. The geology of an area between Bala and Betws-y-Coed, North Wales. Unpublished PhD Thesis, University of Cambridge. |
| Elles, G L. 1922. The Bala country: its structure and rock succession. Quarterly Journal of the Geological Society of London, Vol. 78, 132-175. |
| Schiener, E J. 1970. Sedimentology and petrography of three tuff horizons in the Caradocian sequence of the Bala area (North Wales). Geological Journal, Vol.7, 25-46. |
| Rushton, A W A and Howells, M F. 1998. Stratigraphical framework for the Ordovician of Snowdonia and the Lleyn Peninsula. British Geological Survey Research Report, RR/99/08. |
| Bassett, D A, Whittington, H B, and Williams, A. 1966. The stratigraphy of the Bala district, Merionethshire. Quarterly Journal of the Geological Society of London, Vol. 122, 219-271. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E120
E136
|
