The BGS Lexicon of Named Rock Units — Result Details

Borders Glacigenic Subgroup

Computer Code: BDRGL Preferred Map Code: notEntered
Status Code: Full
Age range: Devensian Stage (QD) — Devensian Stage (QD)
Lithological Description: Suite of glacial, glaciofluvial and glaciolacustrine deposits including sandy diamictons (till), sand, gravel, silt and clay. The sediments were deposited by or are the deglaciation products of ice which emanated from the Southern Uplands and streamed eastwards aound the northern margins of the Cheviot Hills across the Merse of Berwickshire. The deposits contain clasts derived from Devonian and Carboniferous sedimentary rocks (sandstone, siltstone, mudstone) and volcanic and intrusive rocks (basalt, andesite) of the Cheviot Hills and the Kelso district. Varying proportions of Lower Palaeozoic wacke sandstone and siltstone are also present. Tills are generally matrix-supported diamictons with characteristically brownish grey or yellowish grey matrices. However, locally they can be reddish brown, either where the diamictons are weathered or are derived from red strata (e.g. Devonian outcrops).
Definition of Lower Boundary: Sharp, unconformable contact with bedrock. Pre-Ipswichian Quaternary deposits are not proved within the Scottish Borders.
Definition of Upper Boundary: Unconformable contact with units of the Britannia Catchments Group (Tweed Catchments Subgroup) and the British Coastal Deposits Group.
Thickness: To 30m
Geographical Limits: Distributed across the Merse of Berwickshire from the Lammermuir Hills in the north to the margins of the Cheviot Hills in the south. Units of the subgroup might occur locally beyond these geographical boundaries and beyond the approximate surface boundaries with adjacent glacigenic subgroups (e.g. the North Sea Coast Glacigenic Subgroup). Units might also extend offshore,
Parent Unit: Caledonia Glacigenic Group (CALI)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  The glacigenic deposits of the Borders Glacigenic Subgroup are distributed across the Merse of Berwickshire and around the northern margins of the Cheviot Hills. They are dominated by tills but also include glaciofluvial sheet sand and gravels and subglacial (esker) deposits such as the Bedshiels Kames between Greenlaw and Duns. Minor outcrops of glaciolacustrine silty clays are present in small basins, notably between Swinton and Coldstream. 
Reference(s):
McMillan, A A, Hamblin, R J O and Merritt, J W. 2005. An overview of the lithostratigraphical framework for the Quarternary and Neogene deposits of Great Britain (onshore). British Geological Survey Research Report RR/04/04. 
Mitchell, W A. 2005. A reconnaisance of the superficial deposits of the Kale Water, Cheviot Hills, Roxburghshire. British Geological Survey Internal Report IR/05/163. 
Everest, J, Bradwell, T and Golledge, N. 2005. Subglacial landforms of the Tweed palaeo-ice stream. Scottish Geographical Journal, Vol.121. 163-173. 
Geological Survey of Great Britain. Explanation of Sheet 26. Unpublished manuscript 1880s. Additional Information File. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable