The BGS Lexicon of Named Rock Units — Result Details

Blane Water Silt Formation

Computer Code: BLAW Preferred Map Code: notEntered
Status Code: Full
Age range: Devensian Stage (QD) — Devensian Stage (QD)
Lithological Description: The Killearn Borehole (Browne and McMillan, 1989, Plate 1, Figure 8) is the standard section for the Blane Water Silt Formation (0.5-15.61m depth). The typical lithology is of regular interbedded clay and silt forming varves with dark coloured tops. The clays are silty, reddish brown and brownish grey, with grey silt, some sand layers and wisps, and thin beds of diamicton up to 7cm thick. The clay is firm to stiff and of medium to high plasticity. Isolated stones up to 2cm are interpreted as dropstones. Lithological associations of the formation are consistent with deposition of muds on a lake bottom in contact and near to glacier ice.
Definition of Lower Boundary: The Blane Water Silt Formation rests with angular unconformity on older Quaternary sediments including on the Gartocharn Till Formation (GATI) inside the Lock Lomond Stadial ice limit and outside on the Wilderness Till Formation of the Caledonia Glacigenic Group (Midland Valley Glacigenic Subgroup). In Strathblane the formation rests on members of the Clyde Clay Formation.
Definition of Upper Boundary: The Blane Water Silt Formation is overlain conformably and by glaciotectonically emplaced younger sediments of the Drumbeg Sand and Gravel Formation and Gartocharn Till Formation in the Endrick valley outside and at the Loch Lomond Stadial ice limit. In Strathblane it is exposed at the surface.
Thickness: Veneer to over 15m
Geographical Limits: The Blane Water Silt Formation is recognised in the lower Endrick valley near its confluence with Loch Lomond and in the Blane Water valley above Strathblane.
Parent Unit: Central Grampian Glacigenic Subgroup (CGDR)
Previous Name(s): Blane Water Formation [Obsolete Name and Code: Use BLAW] (-3855)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  British Geological Survey Killearn Borehole (Reg.No. NS58SW/3) Browne and McMillan, 1989a, b. 
Type Area  In lower Strath Endrick and Strath Blane. Jardine, W G. 1980. Glasgow region: Field Guide. (Glasgow: Quaternary Research Organisation). 
Reference(s):
Hall, I H S, Browne, M A E and Forsyth, I H. 1998. Geology of the Glasgow district. Memoir of the British Geological Survey, Sheet 30E (Scotland). 
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. 
Jardine, W G (Editor). 1980. Glasgow Region: Field Guide. [Quaternary Reseach Association.] 
Browne, M A E and McMillan, A A. 1989a. Quaternary geology of the Clyde valley. British Geological Survey Research Report, SA/89/1. 
Browne, M A E and McMillan, A A. 1989b. Geology for land use planning: drift deposits of the Clyde valley Volume 1: Planning Report. British Geological Survey Technical Report, WA/89/78. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S030 S038