| Llewelyn Volcanic Group | |
| Type: | Group |
| Age: | Caradoc Ordovician |
| Prilithology: | ash flow tuffs |
| Otherlithology: | rhyolites, mudstones, siltstones, sandstones, breccias etc |
| Namedfor: | Carnedd Llewelyn |
| Region: | northwest Wales |
| Country: | Wales |
| Subunits: | Capel Curig Volcanic Formation, Foel Fras Volcanic Formation, Conwy Rhyolite Volcanic Formation, Foel Grach Basalt Formation, Braich Tu Du Volcanic Formation |
| Underlies: | Cwm Eigiau Formation |
| Overlies: | Nant Ffrancon Formation |
| Thickness: | approx 1400m |
The Llewelyn Volcanic Group is an Ordovician lithostratigraphic group (a sequence of rock strata) in Snowdonia, north-west Wales. The name is derived from Carnedd Llewelyn, the highest peak in the Carneddau range where it outcrops.
The rocks occur across the Snowdon massif and the Carneddau and within the Capel Curig Anticline.[1]
The Group comprises around 1400m thickness of ash flow tuffs, flow-banded rhyolites and breccias with a variety of volcaniclastic sediments erupted or sedimented during the Caradocian epoch of the Ordovician period. The Group comprises (in descending order, i.e. oldest last):
It also includes the Foel Grach Basalt Formation and the Braich Tu Du Volcanic Formation.[2]