The BGS Lexicon of Named Rock Units — Result Details

Deri Formation

Computer Code: DER Preferred Map Code: notEntered
Status Code: Full
Age range: Bolsovian Substage (CC) — Asturian Substage (CAS)
Lithological Description: The Formation comprises mottled red, purple, green and orange mudstones and mudstone palaeosols, pale green siltstones and pale grey quartz arenites and conglomerates. Thin coals fail progressively eastwards towards the Usk Anticline.
Definition of Lower Boundary: The base of the Formation is diachronous and gradational, and placed at the base of the first development of red, green or purple mudstone, where it overlies grey mudstones of the South Wales Coal Measures Group.
Definition of Upper Boundary: The top of the Formation is diachronous and gradational, and placed where the topmost development of red, green or purple mudstone, or white quartz arenite, is overlain by either grey mudstones of the South Wales Coal Measures Group or, on the east crop of the South Wales Coalfield, where it is overlain by the Brithdir Coal, marking the local base of the Pennant Sandstone Formation.
Thickness: To 180m
Geographical Limits: The Formation is confined to the eastern part of South Wales Coalfield, extending from the Cynon Valley near Penrhiwceiber [ST 05 97] eastwards (see Downing and Squirrell, 1965, Figure 1).
Parent Unit: Warwickshire Group (WAWK)
Previous Name(s): Llynfi Beds And Rhondda Beds (-4601)
Deri Beds (-858)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Named after the village of Deri in the Bargoed Rhymney Valley, [SO 13 02], South Wales; the Formation has little natural exposure, and the South Pit [SO 1207 0294] at Ogilvie Colliery [SO10SW/9], Deri (Barclay et al, 1989) provided a reference section from ground surface to 121.08m depth. Howell and Cox, 1924. 
Reference(s):
Howell, A and Cox, A H. 1924. On a group of red measures or coloured strata in the east Glamorgan and Monmouthshire coalfield. Proceedings of the South Wales Institute of Engineers, Vol.43, 139-174. 
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. 
Downing, R A and Squirrell, H C. 1965. On the red and green beds in the Upper Coal Measures of the eastern part of the South Wales Coalfield. Bulletin of the Geological Survey of Great Britain, No.23, 45-56. 
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. 
Squirrell, H C and Downing, R A. 1969. Geology of the South Wales Coalfield, Part 1, the country around Newport (Monmouthshire). Memoir of the Geological Survey of Great Britain, Sheet 249 (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable