Computer Code: |
PT |
Preferred Map Code: |
PT |
Status Code: |
Full |
Age range: |
Caradoc Series (O4)
— Caradoc Series (O4) |
Lithological Description: |
Acid ash-flow tuff; variably welded, rhyolitic. Two main facies - intra caldera tuffs and out-flow tuffs. |
Definition of Lower Boundary: |
Overlies sandstones and mudstones of the Cwm Eigiau Formation. |
Definition of Upper Boundary: |
Overlain by sandstones and siltstones of the Cwm Eigiau Formation or tuffs of the Lower Rhyolitic Tuff Formation. |
Thickness: |
700 m intra caldera facies, 0-100 m outflow facies. |
Geographical Limits: |
From Llwyd Mawr to Dolgarrog, central Snowdonia. |
Parent Unit: |
Snowdon Volcanic Group (SV)
|
Previous Name(s): |
Pitts Head "Tuffs" [Obsolete Name and Code: Use PT]
(-3625)
|
Alternative Name(s): |
none recorded or not applicable
|
Stratotypes: |
Partial Type Section |
Outflow facies, west flanks of Moel Hebog. |
Partial Type Section |
Intra caldera facies. Llwyd Mawr - Cwm Silyn. |
Reference(s): |
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. |
Howells, M F and Smith, M. 1997. Geology of the country around Snowdon. Memoir of the British Geological Survey, Sheet 119 (England and Wales). (London: The Stationery Office). 104pp. |
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). |
Reedman, A J, Howells, M F, Orton, G and Campbell, S D G, 1987. The Pitts Head Tuff Formation: a subaerial to submarine welded ash-flow tuff of Ordovician age, North Wales. Geological Magazine, Vol.124, 427-439. |
1:50K maps on which the lithostratigraphical unit is found, and map code used: |
E119
E106
E134
|