The Mawddach Group is a middle to upper Cambrian lithostratigraphic group (a sequence of rock strata) in Gwynedd, Wales. The name is derived from the river known as the Afon Mawddach.
| Mawddach Group | |
|---|---|
| Stratigraphic range: mid to late Cambrian | |
 Slates of the Dolgellau Formation exposed in the Golwen quarry, near Fairbourne | |
| Type | Group |
| Sub-units | Dol-cyn-Afon Formation, Dolgellau Formation, Ffestiniog Flags Formation, Maentwrog Formation, Clogau Formation |
| Overlies | Harlech Grits Group |
| Thickness | about 2,400 m (7,900 ft) |
| Lithology | |
| Primary | mudstones |
| Other | sandstones, siltstones |
| Location | |
| Region | northwest Wales |
| Country |  United Kingdom |
| Type section | |
| Named for | Afon Mawddach (river) |
Outcrops edit
The rocks are exposed across the Harlech Dome and southern Snowdonia.[1]
Lithology and stratigraphy edit
The Group comprises around 2400m thickness of mudstones, sandstones and siltstones laid down in the marine Welsh Basin during the middle to late Cambrian period. The Group comprises (in descending order i.e. oldest last) the Dol-cyn-Afon Formation, the Dolgellau Formation, the Ffestiniog Flags Formation, the Maentwrog Formation and the Clogau Formation.[2]
References edit
- ^ British Geological Survey 1:50,000 scale geological map (England & Wales) sheets 118, 119, 149
- ^ http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=MWG (BGS on-line lexicon of rock units)