The BGS Lexicon of Named Rock Units — Result Details

Assynt Till Formation

Computer Code: ASTI Preferred Map Code: AST
Status Code: Full
Age range: Devensian Stage (QD) — Devensian Stage (QD)
Lithological Description: Heterogeneous orange-brown to dark grey diamicton with wide ranging sedimentological properties, containing a diverse suite of clast lithologies including Lewisian gneiss, Torridon Group sandstone, Eriboll Formation sandstone (quartzite), Moine Supergroup psammite, Durness Group limestone, Canisp porphy, Borralan syenite and other minor igneous rocks. Orange-brown to dark grey poorly sorted diamicton ranging in texture from poorly consolidated, immature, stony till to over-consolidated, silt-rich, lodgement till. The till is typically autochthonous, being largely derived from the underlying bedrock, however it may also contain reworked glaciofluvial and/or morainic deposits of Devensian age or older.
Definition of Lower Boundary: Unconformable on bedrock.
Definition of Upper Boundary: Overlain locally by Holocene (Flandrian) deposits, typically peat or (glacio)fluvial gravel.
Thickness: Variable, ranges from 0.5-78m (maximum observed thickness).
Geographical Limits: Patchy, discontinuous extent across Wester Ross and western Sutherland, west of the main Highland watershed.The Assynt Till Formation is composed of the following geographically distinct, mappable, members: Unapool Till Member, predominantly overlying Lewisian gneiss; Loch Lurgain Till Member, predominantly overlying Torridon Group sandstone; Allt Sgiathaig Till Member, predominantly overlying Eriboll Formation sandstone (quartzite); Traligill Till Member, predominantly overlying Durness Group limestone; and Allt an t-Strathain Till Member, predominantly overlying Moine Supergroup psammite.
Parent Unit: Northwest Highlands Glacigenic Subgroup (NWHG)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  (Unapool Till Member) Large roadside cutting (A984), 400m north of Unapool House, Loch Glencoul, Sutherland. Bradwell, T. 2003. BGS Internal report IR/03/120. 
Reference Section  (Loch Lurgainn Till Member) Road cutting on unclassified Achiltibuie road, 100m north of Loch Lurgainn, Wester Ross. Bradwell, T. 2003. BGS Internal report IR/03/120. 
Reference(s):
Bradwell, T. 2003. The Quaternary deposits and glacial history of the area around Inchnadamph, Sutherland. BGS Internal Report IR/03/120. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable