| Computer Code: |
DWF |
Preferred Map Code: |
Dwf |
| Status Code: |
Full |
| Age range: |
Longvillian Substage (OL)
— Woolstonian Substage (OS) |
| Lithological Description: |
Medium- to coarse-grained sandstones and subordinate interbedded mudstones (Bodwrog Member), passing upwards into grey calcareous mudstones and siltstones with subordinate sandstones (Plastirion Member). |
| Definition of Lower Boundary: |
Underlain by rhyolitic ash-flow tuff of the Allt Fawr Rhyolitic Tuff Formation. Probably also unconformable on Nant Ffrancon Subgroup mudstones and siltstones, and Upper Lodge Formation lavas and tuffs. |
| Definition of Upper Boundary: |
Overlain by, and partly interbedded laterally with a sequence of lavas and tuffs with some volcaniclastic sediments of the Llanbedrog Volcanic Group. |
| Thickness: |
150 to 600m |
| Geographical Limits: |
Pwllheli area, northwest Wales. |
| Parent Unit: |
Ogwen Group (OGW)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Partial Type Section |
Within the Dwyfach Valley at Plas Talhenbont, northwest of Llanystumdwy. No further details. Young, T P, Gibbons, W and McCarroll, D. 2002. |
| 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. |
| Young, T P, Gibbons, W and McCarroll, D. 2002. Geology of the country around Pwllheli. Memoir of the British Geological Survey, Sheet 134 (England and Wales). |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E134
|
