| Ogwen Group | |
|---|---|
| Stratigraphic range: Arenig to Caradoc Ordovician | |
| Type | Group |
| Sub-units | Allt Llwyd and Wig Bach formations, Nant Ffrancon Subgroup (which includes Llanengan and St Tudwal's formations), Cwm Eigiau, Allt Fawr Rhyolitic Tuff, Dwyfach and Nod Glas formations |
| Overlies | Mawddach Group, Rhobell Volcanic Group |
| Thickness | variable, more than 2 km |
| Lithology | |
| Primary | mudstones, siltstones |
| Other | sandstones, tuffs, oolitic ironstones |
| Location | |
| Region | northwest Wales |
| Country | Wales |
| Type section | |
| Named for | Ogwen Valley |
The Ogwen Group is an Ordovician lithostratigraphic group (a sequence of rock strata) in Gwynedd, north-west Wales. The name is derived from Ogwen Valley, a locality in Snowdonia where it outcrops.