Computer Code: |
GAGO |
Preferred Map Code: |
Gago |
Status Code: |
Full |
Age range: |
Frasnian Age (DR)
— Famennian Age (DA) |
Lithological Description: |
Interbedded sandstones and red-brown mudstones. The sandstones in the basal part are pale grey-green quartzites; those in the upper part are grey-green, soft, friable, richly micaceous and feldspathic. |
Definition of Lower Boundary: |
Erosion surface cut in conglomerates of the Craig-y-cwm Formation, overlain by pale yellow to white micaceous sandstone [Lovell, 1978]. |
Definition of Upper Boundary: |
Sharp junction between overlying limestone of the Castell Coch Limestone of the Lower Limestone Shale Group and the topmost sandstones of the Garn-gofen Formation. A thin but persistent conglomerate marks the base of the Castell Coch Limestone. |
Thickness: |
Up to a maximum of 20 m. |
Geographical Limits: |
From Blaen Onneu - Daren Cilau area near Crickhowell, Gwent eastwards and southwards to Pontypool, Gwent, South Wales. |
Parent Unit: |
Portishead Subgroup (POB)
|
Previous Name(s): |
Sandstones and Marls [Obsolete Name and Code: Use GAGO]
(-2812)
|
Alternative Name(s): |
none recorded or not applicable
|
Stratotypes: |
Type Area |
Exposures at Craig-y-cwm near Garn-gofen Farm, about 3 km. south-east of Blaenavon, Gwent. [Barclay, 1989]. |
Reference(s): |
Barclay, W J. 1975. Annual report for 1974, p. 26. Institute for Geological Sciences: London. |
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. |
Lovell, R W W. 1978a. The sedimentology and stratigraphy of the Upper Old Red Sandstone and Lower Limestone Shales of the South Wales Coalfield. Unpublished PhD thesis, University of Bristol. |
1:50K maps on which the lithostratigraphical unit is found, and map code used: |
E232
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