The BGS Lexicon of Named Rock Units — Result Details

Dowlais Limestone Formation

Computer Code: DWL Preferred Map Code: notEntered
Status Code: Full
Age range: Holkerian Substage (CQ) — Holkerian Substage (CQ)
Lithological Description: Tabular, thick-bedded, mid- to dark grey, fetid, bituminous, fossiliferous, peloidal grainstone, packstone and wackestone limestones with dark grey shale interbeds; minor dark grey, micritic limestones and pale grey ooidal limestones and some local basal sandstones.
Definition of Lower Boundary: The base is placed at a regional unconformity, the basal limestone of the Dowlais Formation overstepping the underlying formations westwards on the north crop of the South Wales Coalfield, from the Llanelly Formation (green and red-mottled clay) in the east to the Avon Group (thinly bedded fissile mudstones and limestones) in the west.
Definition of Upper Boundary: The top is placed at the conformable junction of the dark grey limestones of the Dowlais Formation with the overlying pale grey ooidal limestones of the Penderyn Oolite Member of the Oxwich Head Limestone Formation. From the type area eastwards, the formation is truncated by a pre-Namurian unconformity.
Thickness: To about 120m
Geographical Limits: North crop of the South Wales Coalfield, from Kidwelly [SN 415 077] to Gilwern Hill [SO 2450 1280].
Parent Unit: Pembroke Limestone Group (PEMB)
Previous Name(s): Upper Seminula Zone (S2) Limestone (-3379)
Greenhall Limestone [Obsolete Name And Code: Use DWL] (GHL)
Cil-yr-ychen Limestone [Obsolete Name And Code: Use DWL] (CYL)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Extensive quarries around Morlais Castle, Dowlais, near Merthyr Tydfil, Glamorgan, South Wales. Barclay et al. 1988. 
Reference(s):
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. 
George, T N, Johnson, G A L, Mitchell, M, Prentice, J E, Ramsbottam, W H C, Sevastopulo, G D and Wilson, R B. 1976. A correlation of the Dinantian rocks of the British Isles. Special Report of the Geological Society of London, No 7. 
Barclay, W J, Taylor, K and Thomas, L P, 1988. Geology of the South Wales Coalfield, Part V, the country around Merthyr Tydfil. Third Edition. Memoir of the British Geological Survey, Sheet 231 (England and Wales). 
Robertson, T and George, T N. 1933. The Carboniferous Limestone of the North Crop of the South Wales Coalfield. Proceedings of the Geologists' Association, Vol.49, 18-40. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E232 E230