Ogwen Group

Ogwen Group
Stratigraphic range: Arenig to Caradoc Ordovician
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
Lithology
Primarymudstones, siltstones
Othersandstones, tuffs, oolitic ironstones
Location
Regionnorthwest Wales
CountryWales
Type section
Named forOgwen 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.

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