The BGS Lexicon of Named Rock Units — Result Details

Rhondda Member

Computer Code: RA Preferred Map Code: notEntered
Status Code: Full
Age range: Bolsovian Substage (CC) — 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 of the Member is placed at the base of the No.2 Rhondda Coal in the type area of the Rhondda valleys; the seam is named the Llwydcoed Seam in the Ammanford district and the Wernddu in the Swansea district. The coal rests conformably on lithic ("Pennant") sandstones and thin mudstones/siltstones of the underlying Llynfi Member.
Definition of Upper Boundary: The top is placed at the base of the Brithdir Coal, where the coal overlies thin mudstone/seatearth at the top of the Member and is overlain by lithic ("Pennant") sandstone and thin siltstone/mudstone of the Brithdir Member.
Thickness: Up to 320m in the Swansea - Port Talbot district [c.SS 775 940].
Geographical Limits: South Wales Coalfield; on north crop from Burry Port [SN 42 02] to the Bargoed Taff Valley [SO 115 054] and on the south crop from the Loughor estuary [SS 535 957] to Risca [ST 24 92].
Parent Unit: Pennant Sandstone Formation (PES)
Previous Name(s): Rhondda Formation (-4282)
Rhondda Beds (-2387)
Alternative Name(s): none recorded or not applicable
Type Area  The Type Area is the area of the Rhondda valleys, South Wales. Woodland et al. 1957. 
Reference Section  Ty'n-y-bedw Quarry, Treorchy, Rhondda valley, South Wales provides a reference section. It exposes 44m of massive and cross-bedded sandstones with several beds of siltstone and silty mudstone up to 3m thick. The base of the section lies 3-6m above the No.2 Rhondda Coal, Woodland and Evans, 1964. 
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). 
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:
E232 E231 E230 E246 E247