The BGS Lexicon of Named Rock Units — Result Details

South Wales Upper Coal Measures Formation

Computer Code: SWUCM Preferred Map Code: notEntered
Status Code: Full
Age range: Bolsovian Substage (CC) — Asturian Substage (CAS)
Lithological Description: Grey (productive) coal-bearing mudstones/siltstones with seatearths and minor grey, quartz-rich sandstones, coals and ironstones.
Definition of Lower Boundary: The base of the Formation is placed at the top of the Cambriense (Upper Cwmgorse) Marine Band. Mid-grey mudstones or siltstones conformably overlie darker grey, fossiliferous mudstones of the Cambriense Marine Band, which mark the top of the underlying South Wales Middle Coal Measures (Stubblefield and Trotter, 1957).
Definition of Upper Boundary: The top of the formation is placed at the incoming of the first thick (over c.3m) lithic arenite ("Pennant Sandstone"), where the arenite rests conformably but diachronously on grey mudstones/siltstones at the top of the South Wales Upper Coal Measures Formation. On the east crop of the coalfield, the top is placed at the diachronous incoming of red/green mottled mudstones, which mark the base of the Deri Formation.
Thickness: Up to a maximum of 184m, southwest of Ammanford [SN 58 09].
Geographical Limits: Widespread throughout the South Wales Coalfield, from the Twyi estuary [SN 38 01], west of Pembrey, east to the Rhymney area [SO 120 058] on the north crop of the coalfield and to Risca [ST 24 92] on the south crop.
Parent Unit: South Wales Coal Measures Group (SWCM)
Previous Name(s): Upper Coal Measures (-4912)
Llynfi Beds (-366)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Margam Park No.3 Borehole (SS 88NW/13) provides a refereence section in which the top of the Formation is at 619' 4" (188.77m) and the base at 706' 3" (215.26m) depth. Waters et al., (in prep); Woodland and Evans , 1964. 
Reference(s):
Woodland, A W and Evans, W B. 1964. The Geology of the South Wales Coalfield, part IV the Country around Pontypridd and Maesteg. Memoirs of the Geological Survey of Great Britain, One-Inch Geological Sheet 248 (England and Wales). 
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, 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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable