Ogwen Group
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TypeGroup
Sub-unitsAllt 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
OverliesMawddach Group, Rhobell Volcanic Group
Thicknessvariable, more than 2 km
| 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.