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): Dyserth Limestone Group [Obsolete Name And Code: Use CLWYD] (DYL)
Carboniferous Limestone Series (-2703)
Gronant Group [Obsolete Name And Code: See CLWYD And CRAV] (GRN)
Carboniferous Limestone [Obsolete Name And code] (-4550)
Mountain Limestone (-2100)
Alternative Name(s): none recorded or not applicable
Type Area  The Dinantian outcrop between Prestatyn and LlandegLa in North Wales (see also component formations for reference sections). Davies et al, in press 
Greenly, E. 1919. Geology of Anglesey. Memoir of the Geological Survey, UK. 
Morton, G H 1876-8. The Carboniferous Limestone and Millstone Grit of North Wales. Proceedings of the Liverpool Geological Society. Vol.3, 190-201. 
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. 
Davies, J R, Wilson, D and Williamson, I T. 2004. Geology of the country around Flint. Memoir for 1:50 000 Geological Sheet 108. 
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. 
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. 
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. 
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