The BGS Lexicon of Named Rock Units — Result Details

Gartocharn Till Formation

Computer Code: GATI Preferred Map Code: GATI
Status Code: Full
Age range: Loch Lomond Stadial (Younger Dryas) (QDL) — Loch Lomond Stadial (Younger Dryas) (QDL)
Lithological Description: The Gartocharn Till Formation is of variable lithology reflecting the extremes of deposition by terminal ice front deformation to sub-glacial lodgement processes. At the reference section the deposit is a brown to dark brownish grey silty clayey diamicton with dark sulphide patches and marine shells. The clay is massive and contains isolated pebbles, gravel and boulders, and knots of sand. It is stiff-hard and of medium–high plasticity and is characterised by joints and low angle thrust surfaces. The combined characteristics reflect the nature of the Linwood Clay Member (Clyde Clay Formation) that has been glacially reworked by advancing ice. Elsewhere, inboard from the terminal moraine, the till is a more typical, glacial lodgement diamicton composed of boulders, gravel and pebbles in a sandy silty clay matrix. The constituent clasts are of two general types: a) locally derived rocks of Devonian and Carboniferous ages from the Midland Valley, and b) more generally in the Highlands, Dalradian metamorphic rocks. Quaternary marine shells are locally incorporated.
Definition of Lower Boundary: Unconformity or glacial deformation boundary on older Quaternary strata such as the Linwood Clay Member and the Wilderness Till Formation; also on bedrock. Complex relationships laterally with the lacustrine sediments of the Blane Water Silt Formation and deltaic/lacustrine sediments of the Drumbeg Sand and Gravel Formation (forming part of the Loch Lomond Stadial Terminal Moraine Complex in the Leven and Endrick valleys in the Loch Lomond basin).
Definition of Upper Boundary: Unconformity below younger Quaternary strata or glacial deformation boundary. Where data are available the Gartocharn Till Formation is overlain by the Drumbeg Sand and Gravel Formation and by the Buchanan Clay Member of the Clyde Clay Formation in the Loch Lomond area.
Thickness: Up to more than 6 m.
Geographical Limits: West central Scotland, related to ice streams sourced in the Highlands during the Loch Lomond Stadial; Loch Lomond area including the Leven and Endrick valleys, sea lochs in the northern Firth of Clyde and the Stirling area to the northwest of Callander.
Parent Unit: Central Grampian Glacigenic Subgroup (CGDR)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Loch Lomond Basin within the limits of the Loch Lomond Stadial ice-sheet. 
Reference Section  BGS Mains of Kilmarnock Borehole (BGS Registered No. NS48NW3) (28.07 - 32.99 m depth) (Browne and McMillan, 1989). 
Reference(s):
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. 
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. 
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). 
Rose, J, 1989. Stadial type sections in the British Quaternary, 45-67 in Quaternary Type Sections: Imagination or Reality ? Rose, J and Schluchter (Editors). Balkema, Rotterdam. 
Browne, M A E, McMillan, A A and Hall, I H S. 1983. Blocks of marine clay in till near Helensburgh, Strathclyde. Scottish Journal of Geology, Vol.19, 321-325. 
Rose, J. 1981. Field Guide to the Quaternary of the southeastern part of the Loch Lomond Basin. Proceedings of the Geological Society of Glasgow, Sessions 122/123, 12-28. 
Stoker, M S, McMillan, A A and Waters, C N. Quaternary Stratigraphical Chart: Northern Britain. British Geological Survey, 1 poster. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable