The BGS Lexicon of Named Rock Units — Result Details
Ystog Formation
| Computer Code: | YSTOG | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Devensian Stage (QD) — Holocene Epoch (QH) | ||
| Lithological Description: | Grey, laminated and massive, silty clay and silt. Gravelly shoreline deposits and sandy deltaic deposits are present locally (Cave and Hains, 2001). Likely to contain dropstones and interbedded thin diamictons at depth. | ||
| Definition of Lower Boundary: | Unconformable on bedrock and Plynlimon Glacigenic Formation. Laterally it might interdigitate with head deposits. | ||
| Definition of Upper Boundary: | Generally the ground surface or unconformable contact with Holocene alluvial deposits of the Severn and Avon Catchments Subgroup. | ||
| Thickness: | Likely to be in excess of 10 m. A railway cutting at [SO 1696 9105] exposes 7 m of sand and fine gravel. | ||
| Geographical Limits: | Upper Camlad Valley and Caebitra Valley, upper Mule Valley and lower Camlad Valley, Powys/Shropshire. | ||
| Parent Unit: | Britannia Catchments Group (BCAT) | ||
| Previous Name(s): | Lacustrine deposits
(LDE)
Glaciolacustrine sand and gravel [Obsolete Name and Code: Use GLLD] (-3153) Glaciolacustrine deposits, undifferentiated [Obsolete Name and Code: Use GLLD] (-2546) Lacustrine deposits (LDE) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Reference Section | River bank near Trefeen Bridge exposing up to 7 m of soft, grey, laminated clay deposited in the former Kerry Lake. Cave and Hains, 2001. | ||
| Type Area | Boggy ground in the Caebitra and upper Camlad valleys, in the vicinity of Church Stoke. The deposits are of Lake Camlad-Caebitra, one of a series of interconnected lakes that developed initially in front of Welsh ice during the Late Devensian and persisted against moraines into the Holocene. Pollen analyses have failed to provide a date, persistence into the Holocene is inferred from geomorphological criteria. Cave and Hains, 2001. | ||
| 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. | |||
| Cave, R and Hains, B A. 2001. Geology of the country around Montgomery. Memoir of the British Geological Survey, Sheet 165 with part of 151 (Welshpool) (England and Wales). | |||
| British Geological Survey. 1994. Montgomery. England and Wales. Sheet 165, Solid and Drift Geology. 1:50 000 (Keyworth, Nottingham: British Geological Survey.) | |||
| 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. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E165 | |||