| Garnedd-Wen Formation | |
| Type: | Formation |
| Age: | Hirnantian |
| Period: | Ordovician |
| Prilithology: | Mudstone |
| Otherlithology: | Sandstone |
| Namedfor: | Garneddwen |
| Region: | Mid Wales |
| Country: | Wales |
| Unitof: | Abercorris Group |
| Overlies: | Narrow Vein Mudstone Formation |
| Thickness: | 1000m (3,000feet) to 3000m (10,000feet) |
| Extent: | Tywyn to Dinas Mawddwy |
The Garnedd-Wen Formation (also known as the Garnedd-Wen Beds) is an Ordovician lithostratigraphic formation (a sequence of rock strata) in Mid Wales. The rock of the formation is a mixture of mudstones, siltstones, fine- to coarse-grained sandstones, greywackes and conglomerates.[1] The formation extends from Dinas Mawddwy in the north-east to Tywyn in the south-west.[2]
The Garnedd-Wen Formation is the upper strata of rock across a wide part of western Mid Wales. In particular, it forms the upper rock beds of the Tarren Hills on the south side of the Bala Fault, west of Talyllyn Lake.[3]