The BGS Lexicon of Named Rock Units — Result Details

Clogau Formation

Computer Code: CLU Preferred Map Code: CLu
Status Code: Full
Age range: St David's Series (ED) — St David's Series (ED)
Lithological Description: Black pyritous and carbonaceous mudstones and silty mudstones with rare silt laminae and sparse fine-grained sandstone beds.
Definition of Lower Boundary: Conformably overlies sandstone of the Gamlan Formation (Harlech Grits Group). Boundary is transitional over 5m.
Definition of Upper Boundary: Sharply but unconformably overlain by silty mudstone and sandstone turbidites of the Maentwrog Formation.
Thickness: 90 to 105m
Geographical Limits: Northern, eastern and southern flanks of the Harlech Dome, North Wales.
Parent Unit: Mawddach Group (MWG)
Previous Name(s): Clogau Shales (-792)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Basal part exposed in Afon Llafar, North Wales. 
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. 
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. 
Matley, C A and Wilson, T S. 1946. The Harlech Dome, North of the Barmouth Estuary. Quarterly Journal of the Geological Society of London, Vol.102, 1-40. 
Allen, P M, Jackson, A A, and Rushton, A W A. 1981. The stratigraphy of the Mawddach Group in the Cambrian succession of North Wales. Proceedings of the Yorkshire Geological Society, Vol. 43, 295-329. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E119 E135 E149