The BGS Lexicon of Named Rock Units — Result Details
Eryry Glacigenic Formation
| Computer Code: | ERYG | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Dimlington Stadial (QDD) — Dimlington Stadial (QDD) | ||
| Lithological Description: | Moderately stiff, dark grey to blue-grey, generally massive, pebbly, silty clay, characteristically containing Snowdonian Ordovician volcanic clasts but dominated by local Lower Palaeozoic clasts. Colour and dominant clast composition variable and generally reflect the local bedrock geology. Also includes other glacigenic deposits of similar composition, notably glaciofluvial sand and gravel and morainic deposits. | ||
| Definition of Lower Boundary: | Generally unconformable on bedrock, but locally may overlie Devensian head deposits (McCarroll, 2005, p.29); Lleyn Till Member of St Asaph Glacigenic Formation (Lleyn Formation of Young et al., 2002), or post-Ipswichian pre-glacial peats (Addison and Edge, 1992). | ||
| Definition of Upper Boundary: | Generally the ground surface or unconformable contact with overlying alluvial deposits, peat and head (Britannia Catchemnts Group). May locally be unconformably overlain by red diamicton of the Lleyn Formation (of Harris et al., 1997), Lleyn Till Member, St Asaph Glacigenic Formation (McMillan et al., 2011). | ||
| Thickness: | Highly variable, locally likely to greatly exceed 10 m (Warren et al., 1984). | ||
| Geographical Limits: | Mountains of Snowdonia, Rhinogs and Cadair Idris; eastern Lleyn Peninsula. | ||
| Parent Unit: | Wales Glacigenic Subgroup (WALES) | ||
| Previous Name(s): | Welsh Till [Obsolete Name and Code: Use ERYG]
(-3390)
North Welsh Boulder Clay [Obsolete Name and Code: Use ERYG] (-1529) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Type Section | Pen-y-bryn brickworks, Caernarfon. Succession of Irish Sea-derived till on Welsh-provenanced till and glaciofluvial gravels on biogenic muds sands and gravels (Addison and Edge, 1992; Bowen, 1999) | ||
| Reference(s): | |||
| Bowen, D Q. 1999. Wales. Chapter 7 in A revised correlation of Quaternary deposits in the British Isles. Bowen, D Q (editor). 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. | |||
| 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). | |||
| Whittow, J B and Ball, D F. 1970. North-west Wales. In Lewis, CA. (ed) The glaciations of Wales and adjoining regions. Longman Press. | |||
| Addison, K, and Edge, M J. 1992. Early Devensian interstadial and glacigenic sediments in Gwynedd, North Wales. Geological Journal, 27, 181-190. | |||
| Chambers,F M, Addison, K, Blackford, J J, and Edge, M J. 1995. Palynology of organic beds below Devensian glacigenic sediments at Oen-y-Bryn, Gwynedd, North Wales. Journal of Quaternary Science, Vol. 10, 157-173. | |||
| 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. | |||
| McMillan, A A, Hamblin, R J O, and Merritt, J W. 2011. A lithostratigraphical framework for onshore Quaternary and Neogene (Tertiary) superficial deposits of Great Britain and the Isle of Man. British Geological Survey Research Report, RR/10/03. 343pp. | |||
| McCarroll, D. 2005. Northwest Wales. In Lewis, C A and Richards, A E (editors). The glaciations of Wales and adjacent areas. (Logaston Press.) | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| none recorded or not applicable | |||