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Mawddach Group

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Mawddach Group
Stratigraphic range: mid to late Cambrian
Slates of the Dolgellau Formation exposed in the Golwen quarry, near Fairbourne
TypeGroup
Sub-unitsDol-cyn-Afon Formation, Dolgellau Formation, Ffestiniog Flags Formation, Maentwrog Formation, Clogau Formation
OverliesHarlech Grits Group
Thicknessabout 2,400 m (7,900 ft)
Lithology
Primarymudstones
Othersandstones, siltstones
Location
Regionnorthwest Wales
Country United Kingdom
Type section
Named forAfon Mawddach (river)

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.

Outcrops

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The rocks are exposed across the Harlech Dome and southern Snowdonia.[1]

Lithology and stratigraphy

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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

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  1. ^ British Geological Survey 1:50,000 scale geological map (England & Wales) sheets 118, 119, 149
  2. ^ http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=MWG (BGS on-line lexicon of rock units)