Computer Code: |
MW |
Preferred Map Code: |
Mw |
Status Code: |
Full |
Age range: |
St David's Series (ED)
— Merioneth Series (EM) |
Lithological Description: |
Interbedded mudstones, coarse-grained sandstones and fine-grained turbiditic sandstones. The upper part of the Formation is dominated by mudstones. |
Definition of Lower Boundary: |
Underlain by black mudstones of the Clogau Formation. Sharp contact, possible a non-sequence or disconformity. |
Definition of Upper Boundary: |
Conformable and gradational up into sandstones and mudstones of the Ffestiniog Flags Formation, with change in mudstone colour from pale to dark grey. |
Thickness: |
Unknown in detail, 500 to 1200 m. |
Geographical Limits: |
Northern, eastern and southern flanks of the Harlech Dome. |
Parent Unit: |
Mawddach Group (MWG)
|
Previous Name(s): |
none recorded or not applicable
|
Alternative Name(s): |
none recorded or not applicable
|
Stratotypes: |
Partial Type Section |
Afon Hirgwm just upstream of Vigra Bridge, Bontddu. |
Reference(s): |
Allen, P M, and Jackson, A A. 1985. Geology of the country around Harlech. Memoir of the British Geological Survey, Sheet 135 with part of Sheet 149 [England and Wales]. [London: HMSO.] 112pp. |
Pratt, W T, Woodhall, D G and Howells, M F. 1995. Geology of the country around Cadair Idris. Memoir of the British Geological Survey, Sheet 149. (England and Wales). (London: HMSO), 111pp |
Waters, C N, Smith, K, Hopson, P M, Wilson, D, Bridge, D M, Carney, J N, Cooper, A H, Crofts, R G, Ellison, R A, Mathers, S J, Moorlock, B S P, Scrivener, R C, McMillan, A A, Ambrose, K, Barclay, W J, and Barron, A J M. 2007. Stratigraphical Chart of the United Kingdom: Southern Britain. British Geological Survey, 1 poster. |
1:50K maps on which the lithostratigraphical unit is found, and map code used: |
E135
E119
E149
E134
|