The BGS Lexicon of Named Rock Units — Result Details

Coed Ffyddlwn Formation

Computer Code: COFYD Preferred Map Code: notEntered
Status Code: Full
Age range: Courceyan Substage (CF) — Courceyan Substage (CF)
Lithological Description: The lower part comprises fine-grained dolostones, the upper part (the Darren Ddu Limestone Member) comprises thinly bedded micritic limestones, fine grainstones and mudstones.
Definition of Lower Boundary: The base is a sharp junction between the topmost ooidal grainstone of the underlying Blaen Onnen Oolite Formation and the basal dolostones of the Coed Ffyddlwn Formation.
Definition of Upper Boundary: The top is a sharp erosion surface overlain by the basal, coarse grainstone (Craig-y-Gaer Coral Bed) of the overlying Gilwern Oolite Formation.
Thickness: To 18m
Geographical Limits: Northeast crop of the South Wales Coalfield, from Chwar Pant-y-rhiw [SO 2020 1560] southeast to about the area of Gallowsgreen Quarry, Varteg Hill [SO 2662 0677].
Parent Unit: Clydach Valley Subgroup (CLD)
Previous Name(s): Beds 5 And 6 (-802)
Alternative Name(s): none recorded or not applicable
Type Section  Clydach gorge, 2km east of Brynmawr, South Wales. Here the Formation has a sharp base, rests on the Blaen Onnen Oolite Formation and is 14m thick. It comprises mainly fine-grained, homogeneous dolostones and, in the topmost 2m, micritic limestones (the Darren Ddu Limestone Member. Barclay, 1989. 
Barclay, W J, Jackson, D I, Mitchell, M, Owen, B, Riley, N J, White, D E, Strong, G E and Monkhouse, R A. 1989. Geology of the South Wales Coalfield, Part II, the country around Abergavenny. Memoir of the British Geological Survey. 
George, T N. 1954. Pre-Seminulan Main Limestone of the Avonian Series in Breconshire. Quarterly Journal of the Geological Society of London, Vol.110, 282-322. 
1:50K maps on which the lithostratigraphical unit is found, and map code used: