| 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
|
| Stratotypes: |
| 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. |
| 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
|
