The BGS Lexicon of Named Rock Units — Result Details

Clwyd Limestone Group

Computer Code: CLWYD Preferred Map Code: notEntered
Status Code: Full
Age range: Chadian Substage (CI) — Brigantian Substage (CX)
Lithological Description: Diverse range of limestone facies with subordinate sandstone and mudstone units, and exhibiting local dolomitisation. Records the initiation and growth of a carbonate platform along the northern flank of the Wales-Brabant Massif.
Definition of Lower Boundary: In places conformably succeeds reddened siliciclastic facies of the "Basement Beds"; elsewhere rests with marked unconformity on Lower Palaeozoic rocks.
Definition of Upper Boundary: Conformable base of Pentre Chert Formation or Cefn-y-fedw Sandstone Formation in northeast Wales; elsewhere marked by an unconformity with younger Carboniferous or Permo-Triassic rocks.
Thickness: To 900m
Geographical Limits: Crops out on Anglesey (SH 50 80) and on the North Wales mainland between Bangor (SH 54 70) and Oswestry (SJ 27 23); and on the Corwen Outlier (SJ 05 43).
Parent Unit: Carboniferous Limestone Supergroup (CL)
Previous Name(s): Carboniferous Limestone [Obsolete entry, see Supplementary Information] (-4550)
Mountain Limestone (-2100)
Carboniferous Limestone Series (-2703)
Gronant Group [Obsolete Name And Code: See CLWYD And CRAV] (GRN)
Dyserth Limestone Group [Obsolete Name And Code: Use CLWYD] (DYL)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  The Dinantian outcrop between Prestatyn and LlandegLa in North Wales (see also component formations for reference sections). Davies et al, in press 
Reference(s):
Davies, J R, Wilson, D and Williamson, I T. 2004. Geology of the country around Flint. Memoir for 1:50 000 Geological Sheet 108. 
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. 
Greenly, E. 1919. Geology of Anglesey. Memoir of the Geological Survey, UK. 
Wedd, C B, Smith, B and Wills, L J. 1927. The geology of the country around Wrexham, Part 1. Lower Palaeozoic and Lower Carboniferous rocks. Memoir of the Geological Survey of Great Britain. [London: HMSO.] 179pp. 
Howells M F, Reedman A J and Leveridge B E. 1985. Geology of the country around Bangor: Explanation for 1:50 000 geological sheet 106 (England and Wales). British Geological Survey Sheet Explanation. [London: HMSO.] 34pp. 
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. 
Wedd, C B, Smith, B, King, W B R and Wray, D A. 1929. Geology of the country around Oswestry. Memoir of the Geological Survey of Great Britain, Sheet 137. 
Morton, G H 1876-8. The Carboniferous Limestone and Millstone Grit of North Wales. Proceedings of the Liverpool Geological Society. Vol.3, 190-201. 
Warren, P T, Price, D, Nutt, M J C and Smith, E G. 1984. Geology of the country around Rhyl and Denbigh. Memoir for 1:50 000 geological sheets 95 and 107 and parts of sheets 94 and 106. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E096 E093 E094 E095 E105 E106 E107 E108 E120 E121 E137