The BGS Lexicon of Named Rock Units — Result Details

Darren Ddu Limestone Member

Computer Code: DDLM Preferred Map Code: notEntered
Status Code: Full
Age range: Courceyan Substage (CF) — Courceyan Substage (CF)
Lithological Description: Thinly bedded, pale grey micritic limestones (lime mudstones), locally peloidal, with grey-green mudstones and cream laminated dolomitic mudstones; algal laminite locally at the top.
Definition of Lower Boundary: The base is placed at the sharp, planar junction between pale grey lime mudstone at the base of the Member and the underlying fine-grained dolostone of the lower part of the Coed Ffyddlwn Formation.
Definition of Upper Boundary: The upper boundary is placed at an irregular, stylolitized surface cut in the topmost pale grey lime mudstones of the Member, which is overlain by a coarse bioclastic grainstone (the Craig-y-Gaer Coral Bed) at the base of the Gilwern Oolite Formation.
Thickness: 2 to 3m
Geographical Limits: Clydach valley, on the northeast crop of the South Wales Coalfield [SO 215 125].
Parent Unit: Coed Ffyddlwn Formation (COFYD)
Previous Name(s): Bed 6 (part of Marker Beds) (-4600)
Clydach Beds (-1440)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  A small disused quarry [SO 2194 1290] on Darren Ddu, Clydach Valley, 2km east of Brynmawr, Blaenau-Gwent, South Wales exposes 2.36m of thinly bedded lime mudstones, grey-green mudstones and dolomitic mudstones resting with sharp planar contact on fine-grained dolostones. Barclay, 1989. 
Reference(s):
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. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E232