| Computer Code: |
PWCO |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Courceyan Substage (CF)
— Courceyan Substage (CF) |
| Lithological Description: |
Pale grey ooidal grainstone. |
| Definition of Lower Boundary: |
The base is placed at an irregular, palaeokarstic surface cut in underlying dolostones of the Sychnant Dolomite Formation, which is overlain by ooidal grainstones of the Pwll-y-Cwm Oolite Formation. |
| Definition of Upper Boundary: |
The top is a sharp, planar boundary at which the topmost ooildal limestones of the Pwll-y-Cwm Oolite Formation are overlain by buff dolostones of the Pantydarren Formation. |
| Thickness: |
c.7m; 7.6m at Type Section. |
| Geographical Limits: |
Northeast crop of the South Wales Coalfield, correlation at Cwar-yr-Hendre [SO 090 146] is uncertain, but the basal 2-4m of ooidal grainstone of the sequence there is the Pwll-y-Cwm Oolite, it extends eastwards from there to Craig-yr-Hafod [SO 2720 1001] where it is dolomitized. |
| Parent Unit: |
Clydach Valley Subgroup (CLD)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
River gorge section at Pwll-y-Cwm in the Clydach River near Brynmawr, south Wales. Here, at the eponymous type locality, the Pwll-y-Cwm Oolite Formation is 7.6m thick and forms a waterfall. It is sharply overlain by fine-grained dolostone of the Pantydarren Formation. Barclay, 1989. |
| Reference Section |
Roadside section on the Heads of the Valleys road (A456) in the Clydach valley, 2km east of Brynmawr, South Wales provides a more accessible section than the type section. The palaeokarstic surface forming the base of the Formation is exposed. Barclay, 1989. |
| Reference(s): |
| 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: |
|
E232
|
