The BGS Lexicon of Named Rock Units — Result Details

Swansea Member

Computer Code: SW Preferred Map Code: notEntered
Status Code: Full
Age range: Asturian Substage (CAS) — Asturian Substage (CAS)
Lithological Description: Green-grey, lithic arenites ("Pennant sandstones") with thin mudstone/siltstone and seatearth interbeds, and mainly thin coals.
Definition of Lower Boundary: The base is placed at the base of the Golden Seam (Swansea Three Feet or Graigola) (Woodland et al., 1957), where the coal rests on mudstone seatearth within a predominantly arenaceous sequence of the Pennant Sandstone Formation.
Definition of Upper Boundary: The top is placed at the base of the Wernffraith Seam (correlated with the Mynyddislwyn Seam of the eastern part of the South Wales Coalfield) where the coal overlies mudstone seatearth with a predominantly arenaceous sequence of the Pennant Sandstone Formation, and is overlain conformably by the mudstone-dominated succession of the Grovesend Formation.
Thickness: 274m to 290m
Geographical Limits: Western part of the South Wales Coalfield, from Llanelli [SN 49 01] to the Neath area [c.SS 75 97].
Parent Unit: Pennant Sandstone Formation (PES)
Previous Name(s): Swansea Member [Obsolete Code: Use SW] (SWAM)
Swansea Beds (-4911)
Swansea Formation (-3704)
Alternative Name(s): none recorded or not applicable
Reference Section  There is no designated stratotype, the Member being named from the Swansea district (Woodland et al, 1957). Allt-y-fran Quarry, Tyrfran, Llanelli provides a reference section in which 9.9m of mudstones and siltstones overlie "Pennant" sandstones (Barclay, in prep.) Woodland et al., 1957; Barclay, in prep. 
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. 
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. 
Barclay, W J, in prep. Geology of the country around Swansea. Sheet Description of the British Geological Survey. 1:50 000 Sheet 247 Swansea (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E246 E248 E247 E230