The BGS Lexicon of Named Rock Units — Result Details

Wales Glacigenic Subgroup

Computer Code: WALES Preferred Map Code: notEntered
Status Code: Full
Age range: Devensian Stage (QD) — Devensian Stage (QD)
Lithological Description: Suite of glacial, glaciofluvial and glaciolacustrine deposits including sandy diamictons (till), sand, gravel, silt and clay. The sediments were deposited by, or are the deglaciation products of, ice that emanated from the Welsh mountains and radiated across Wales and the Welsh Border. The till deposits vary in colour and clast content reflecting local bedrock. Constituent formations include the Brecknockshire Till Formation containing clasts derived predominantly from the Devonian (Black Mountain, Fforest Fawr and Brecon Beacons) and Carboniferous sources (sedimentary rocks of the South Wales Coalfield), the Plynlimon Till Formation and Shrewsbury Glacigenic Formation containing Lower Palaeozoic clasts of the Cambrian Mountains and the Eryri Till Formation with Lower Palaeozoic volcanic clasts derived from Snowdonia. The till formations contain subordinate stratified sand and gravel. The principal centres of ice build-up were the Cambrian Mountains.
Definition of Lower Boundary: Generally sharp, unconformable contact with bedrock. Locally on Head of Ipswichian or early Devensian age or on units of the Irish Sea Coast Glacigenic Subgroup (e.g. Stockport Glacigenic Formation).
Definition of Upper Boundary: Unconformable contact with units of the Britannia Catchments Group (West Wales Catchments Subgroup and Cheshire-North Wales Catchments Subgroup) and the British Coastal Deposits Group.
Thickness: To 30m
Geographical Limits: South, southeast, mid and northeast Wales and Welsh Borderland.
Parent Unit: Caledonia Glacigenic Group (CALI)
Previous Name(s): Eryri Formation (-2914)
Glamorgan Formation (-3114)
Meirion Formation (*926)
Brecknockshire Formation (-4482)
Elenid Formation (*933)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  The glacigenic deposits of the Wales Glacigenic Subgroup are distributed across southern, mid and northeast Wales and the Welsh Borderland. Bowen, 1999 The deposits are extensively present at surface and are locally overlain by unit of the Britannia Catchments and British Coastal Deposits groups. They rest unconformably on mainly Lower Palaeozoic to Carboniferous strata from which they are derived. Constituent formations may be interbedded with those of the Irish Sea Coast Glacigenic Subgroup. See also the stratotypes of constituent formations including the Brecknockshire, Plynlimon Till, Shrewsbury Glacigenic and Eryri Till formations. 
Reference(s):
Pocock R W, Whitehead T H, Wedd C B and Robertson T. 1938. Shrewsbury District including the Hanwood Coalfield. Memoir of the Geological Survey of Great Britain, England and Wales. (London: H.M.S.O.). 
McCarroll, D. 2005. Northwest Wales. In Lewis, C A and Richards, A E (editors). The glaciations of Wales and adjacent areas. (Logaston Press.) 
Whitlow, J B and Ball, D F. 1970. Northwest Wales. In Lewis, C A (Editor). The glaciations of Wales and adjoining regions. (Longman Press.) 
Campbell, S and Bowen, D Q. 1989. Quaternary of Wales. Geological Conservation Review. (Peterborough: Nature Conservancy Council.) 
Addison, K and Edge, M J. 1992. Early Devensian interstadial and glacigenic sediments in Gwynedd, North Wales. Geological Journal, 27, 181-190. 
Cannell, B. 1982. The sand and gravel resources of the country around Shrewsbury, Shropshire: Description of 1:25 000 sheets SJ41 and SJ51. Mineral Assessment Report, Institute of Geological Sciences, 90, 149pp. 
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. 
Young, T P, Gibbons, W and McCarroll, D. 2002. Geology of the country around Pwllheli. Memoir of the British Geological Survey, Sheet 134 (England and Wales). 
Bowen, D Q, 1999. Wales. Chapter 7 in Bowen, D Q (Editor), A revised correlation of Quaternary deposits in the British Isles. Geological Society of London Special Report, No.23. 
Harris, C, Williams, G, Brabham, P, Eaton, G and McCarroll, D. 1997. Glaciotectonized Quaternary sediments at Dinas Dinlee, Gwynedd, North Wales and their bearing on the style of deglaciation in the Eastern Irish Sea Basin. Quaternary Science Reviews, 16, 109-127. 
Barclay, W J, Davies, J R, Humpage, A J, Waters, R A, Wilby, P R, Williams, M and Wilson, D. 2005. Geology of the Brecon district - a brief explanation of the geological map Sheet 213 Brecon. Sheet explanation of the British Geological Survey. 1:50000 Sheet 213 Brecon. 
Thomas, G S P. 1989. The Late Devensian glaciation along the western margin of the Cheshire-Shropshire lowland. Journal of Quaternary Science, Vol.4(2), 167-181. 
Worsley, P. 2005. The Cheshire-Shropshire Plain. Chapter 5 in Lewis, C A and Richards, A E (editors), The glaciations of Wales and adjacent areas. (Logaston Press.) 
Bowen, D Q. 2005. South Wales. In Lewis, C A and Richards, A E (editors), The glaciations of Wales and adjacent areas. (Logaston Press.) 
McMillan, A A, Hamblin, R J O and Merritt, J W. 2005. An overview of the lithostratigraphical framework for the Quarternary and Neogene deposits of Great Britain (onshore). British Geological Survey Research Report RR/04/04. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable