The BGS Lexicon of Named Rock Units — Result Details
South Wales Coal Measures Group
| Computer Code: | SWCM | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Langsettian Substage (CA) — Bolsovian Substage (CC) | ||
| Lithological Description: | Grey (productive) coal-bearing mudstones/siltstones with seatearths and minor sandstones. | ||
| Definition of Lower Boundary: | The base is placed at the base of the Subcrenatum Marine Band, either in a sequence of mudrocks at the point where a marine fauna makes its first appearance, or where marine mudstone of the Subcrenatum Marine Band overlies quartzites of the underlying Telpyn Point Sandstone Formation of the Marros Group. | ||
| Definition of Upper Boundary: | The top is taken at the base of the Pennant Sandstone Formation (Warwickshire Group), where grey, productive coal-bearing mudrocks of the South Wales Coal Measures Group are overlain conformably either by the first substantial development of Pennant sandstones or by red beds of the Deri Formation. | ||
| Thickness: | c.240m on the east crop of the coalfield to c.900m in the Swansea area. | ||
| Geographical Limits: | South Wales Coalfield; from Pembrokeshire [SM 86 15] in the west eastwards to Abersychan, Monmouthshire [SO 29 02]. It extends from the Black Mountain [SN 670 215] in the north, southwards to Swansea - Port Talbot [SS 80 85] and crops out in a peripheral belt around the coalfield, concealed below the Pennant Sandstone Formation over most of the coalfield. The group is also recorded in the Bristol-Somerset area. The Bristol Coalfield includes the Kingswood Anticline [ST 65 73] and Coalpit Heath Syncline [ST 85 83] to the east and north-east of Bristol, while the Somerset Coalfield comprises the Pensford [ST 65 65] and Radstock synclines [ST 65 55] to the south-east. The Avonmouth [ST 53 80] and Nailsea [ST 45 70] synclines contain coal basins that are structurally distinct, although linked to the major coalfields in the subsurface. The group has also been proved in the subsurface in the Berkshire Coalfield [SU 70 66] and Kent Coalfield [TR 30 40]. | ||
| Parent Unit: | Coal Measures Supergroup (COME) | ||
| Previous Name(s): | Coal Measures Group
(CM)
Coal Measures [Obsolete Name and Code: Use COME] (-4355) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Reference Section | Stream exposures in Cwm Gwrelych - Nant Llyn Fach - Glyn Neath area, extending south from Pont Walby, 1km east of Glyn Neath, West Glamorgan. Robertson, 1932.; Cleal and Thomas, 1996; Evans et al., 2003. | ||
| Type Area | Type area is the South Wales Coalfield and its western extension in Pembrokeshire [SM 86 15], from where it extends eastwards to Abersychan, Monmouthshire [SO 29 02]. It extends from the Black Mountain [SN 670 215] in the north, southwards to Swansea - Port Talbot [SS 8085] and crops out in a peripheral belt around the coalfield, concealed below the Pennant Sandstone Formation over most of the coalfield. Waters et al., (in prep). | ||
| Reference(s): | |||
| Waters, C N, Barclay, W J, Davies, J R and Waters, R A. In press. Stratigraphical framework for Carboniferous successions of Southern Great Britain (Onshore). British Geological Survey Research Report, RR/05/06. | |||
| Cleal, C J and Thomas, B A. 1996. Cwm Gwrelych - Nant Llyn Fach. 83-89 in Cleal, C J and Thomas, B A (editors), British Upper Carboniferous stratigraphy. [London: Chapman and Hall.] | |||
| Evans, B G, Cleal, C J, Thomas, B A and Wimbledon, W A P. 2003. The Westphalian succession of the Glyn-neath area, South Wales; an internationally important geological resource. Proceedings of the Geologists' Association, Vol.114, 291-305. | |||
| Stubblefield, C J and Trotter, F M, 1957. Divisions of the Coal Measures on Geological Survey Maps of England and Wales. Bulletin of the Geological Survey of Great Britain, No.13, p.1-5. | |||
| Woodland, A W, Evans, W B and Stephens, J V. 1957. Classification of the Coal Measures of South Wales with Special reference to the Upper Coal Measures. Bulletin of the Geological Survey of Great Britain, No. 13, 39-60. | |||
| Waters, C N, Waters, R A, Barclay, W J, and Davies, J R. 2009. Lithostratigraphical framework for Carboniferous successions of Southern Great Britain (Onshore). British Geological Survey Research Report, RR/09/01. 184pp. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| none recorded or not applicable | |||