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): |
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. |
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. |
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. |
Campbell, S D G. 1983. The geology of an area between Bala and Betws-y-Coed, North Wales. Unpublished PhD Thesis, University of Cambridge. |
1:50K maps on which the lithostratigraphical unit is found, and map code used: |
E120
E136
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