The BGS Lexicon of Named Rock Units — Result Details

Teifi Clay Formation

Computer Code: TFICL Preferred Map Code: notEntered
Status Code: Full
Age range: Devensian Stage (QD) — Devensian Stage (QD)
Lithological Description: Brown and grey clay and silt laminated clay, with interbeds of grey/yellow stratified silt and fine sand, which locally increases in abundance towards the top. Dropstones are locally abundant and form thin beds of diamicton. Clasts are dominated by local bedrock lithologies but characteristically include shell fragments.
Definition of Lower Boundary: Unconformable on bedrock or contact with ?Late Devensian regolith, head and fluvial deposits.
Definition of Upper Boundary: Ground surface (sheared) contact with overlying Lleyn Formation, or unconformable with fluvioglacial deposits of the Lleyn Formation and Plynlimon Till Formation, West Wales Catchments Subgroup (peat and fluvial deposits).
Thickness: Up to 75m in a borehole at Llwynpiod [SN14NE/156]
Geographical Limits: South Ceredigion, north Pembrokeshire and north Carmarthenshire (Wales). Predominantly within pre-glacial valley systems.
Parent Unit: Irish Sea Coast Glacigenic Subgroup (ISCG)
Previous Name(s): Llechryd Member (-2481)
Glaciolacustrine Deposits (GLLD)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  BGS Llwynpiod (Cardigan 1) borehole [SN14NE/156], depth 0-77m. 
Type Section  BGS Pen-y-Bryn (Cardigan 2) borehole [SN14SE/12] depth 3-64m. Hambrey et al., 2001. The type section forms part of the fill of a buried abandoned meander loop of the Afon Teifi and was deposited within a former proglacial lake system that developed in front of advancing Irish Sea Ice as it dammed the mouths of rivers along the Cardiganshire coast. The unit typically coarsens uowards, indicating advance of the ice into the lake basin(s), and contains shell material derived from the Irish Sea Basin. 
Reference(s):
Jones, O T, 1965. The glacial and post-glacial history of the lower Teifi valley. Quaterly Journal of the Geological Society of London, Vol.121, 247-281. 
Fletcher, C J N and Siddle, H J. 1998. Development of glacial Llyn Teifi, west Wales: evidence for lake-level fluctuations at the margins of the Irish Sea Ice sheet. Journal of the Geological Society of London, Vo.155, 398-399. 
Davies, J R, Waters, R A, Wilby P R, Williams, M and Wilson, D. 2003. Geology of the Cardigan and Dinas Island district - a brief explanation of the geological map. Sheet explanation of the British Geological Survey. 1: 50 000 Sheet 193. [Keyworth, Nottingham: British Geological Survey.] 26pp. 
Etienne, J L, Jansson, K N, Glasser, N F, Hambrey, M J, Davies, J R, Waters, R A, Maltman, A J and Wilby, P R. 2006. Palaeoenvironmental interpretation of an ice-contact glacial lake succession: an example from the Late Devensian of southwest Wales. UK Quaternary Science Reviews, Vol.25, 739-762. 
Hambrey, M J, Davies, J R, Glasser, N F, Waters, R A , Dowdeswell, J A, Wilby, P R, Wilson, D and Etienne, J L. 2001. Devensian glacigenic sedimentation and landscape evolution in the Cardigan area of southwest Wales. Journal of Quaternary Science, 16, 455-482. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E193 E194 E211 E210