| Computer Code: |
OGW |
Preferred Map Code: |
OG |
| Status Code: |
Full |
| Age range: |
Arenig Series (OR)
— Caradoc Series (O4) |
| Lithological Description: |
Mudstones and siltstones, but including basal sandstone units and other sandstones, tuffs and oolitic ironstones. |
| Definition of Lower Boundary: |
Base of the Allt Lwyd Formation, at unconformable boundary overlying the Mawddach Group and Rhobell Volcanic Group. |
| Definition of Upper Boundary: |
Top of the Nod Glas Formation . |
| Thickness: |
c.1000m Pwllheli District. |
| Geographical Limits: |
Gwynedd, North Wales. |
| Parent Unit: |
Not Applicable (-)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Area |
Extends from Cwm Graianog in Nant Ffrancon, along the Ogwen and Llugwy valleys towards the syncline south-west of Grinllwm. |
| 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. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E135
E118
|
