The BGS Lexicon of Named Rock Units — Result Details
Garn Caws Sandstone Formation
| Computer Code: | GACA | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Arundian Substage (CJ) — Arundian Substage (CJ) | ||
| Lithological Description: | White, silica-cemented ("quartzitic") sandstones and conglomerates with some thin intercalated plant-bearing green-grey mudstones and seatearth. | ||
| Definition of Lower Boundary: | The base is placed at the base of silica-cemented ("quartzitic") sandstone or conglomerate where it rests with sharp base on an erosion surface cut in the underlying Gilwern Clay Member of the Llanelly Formation. | ||
| Definition of Upper Boundary: | The top is placed at the top of the silica-cemented ("quartzitic") sandstone, where it is sharply and unconformably overlain by the basal limestone of the Dowlais Limestone Formation. | ||
| Thickness: | To 12m (maximum at Blaen Onneu Quarry [SO 155 169]. | ||
| Geographical Limits: | Northeast crop of the South Wales Coalfield, from the area of Cwar yr Hendre [SO 099 149] eastwards to the type area of Garn Caws [SO 120 164], and farther eastwards to the Clydach Valley [c.SO 215 127]. | ||
| Parent Unit: | Pembroke Limestone Group (PEMB) | ||
| Previous Name(s): | Gilwern Clay Member
(GWCL)
Gilwern Clay Member (GWCL) Garn Caws Sandstone [Obsolete Name and Code: Use GACA] (-271) Dowlais Limestone [Obsolete Name and Code: Use GACA] (-1551) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Type Area | Extensive exposures on the hill of Garn Caws, Powys. Barclay, 1989. | ||
| Reference Section | Excellent exposures at Blaen Onneu Quarry, Powys, show 12 m of quartzitic (silica-cemented) sandstone with some thin green-grey, plant-bearing mudstone beds. Wright, 1981; Barclay, 1989. | ||
| Reference(s): | |||
| Barclay, W J, and Jackson, D I. 1982. The geology of Carno adit, Ebbw Vale, South Wales. Report of the Institute of Geological Sciences, No. 82/1, 41-44. | |||
| Dickson, J A D and Wright, V P. 1993. Carboniferous Limestone of the north crop of the South Wales Coalfield. 331-349 in Woodcock, N H and Bassett, M G (editors), Geological excursions in Powys, central Wales. [Cardiff: University of Wales Press, National Museum of Wales.] | |||
| 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. | |||
| Wright, V P. 1981. Llanelly Formation. 36-72 in Wright, V P, Raven, M and Burchette, T P (editors), A field guide to the Carboniferous Limestone around Abergavenny. [Cardiff: Department of Geology, University College of Wales.] | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E232 | |||