The BGS Lexicon of Named Rock Units — Result Details

Allt Sgiathaig Till Member

Computer Code: SGTI Preferred Map Code: BQT
Status Code: Full
Age range: Devensian Stage (QD) — Devensian Stage (QD)
Lithological Description: Pinkish off-white, pale grey to mid grey, poorly sorted, sandy, clast-rich diamicton with boulders. The till has a quartz-sand matrix devoid of clay. Clasts are typically angular and densely packed. Clasts are predominantly of Cambrian Eriboll Formation sandstone (Basal Quartzite and Pipe Rock Member), although rare Lewisian gneiss, Torridon Group sandstone, Moine Supergroup and local igneous clasts may occur. The till is typically autochthonous, being derived from the local quartzite bedrock. Local underlying lithological variations (eg. Assynt imbricate zones) may be reflected by clast lithologies (eg. Salteralla Grit, Durness Limestone, Fucoid Beds, etc.).
Definition of Lower Boundary: Unconformable on bedrock, predominantly Eriboll Formation sandstone.
Definition of Upper Boundary: Overlain locally by Holocene (Flandrian) deposits, typically peat or (glacio)fluvial gravel.
Thickness: Variable; 0.2-5m (maximum observed thickness).
Geographical Limits: Patchy, discontinuous extent within the outcrop of the Moine Thrust Belt, between Ullapool and Loch Eriboll. Occurs exclusively to the west of the Moine Thrust and predominantly on Eriboll Formation sandstone.
Parent Unit: Assynt Till Formation (ASTI)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Large roadcut in Basal Quartzite (A837), 400m west of Skiag Bridge, Loch Assynt, Sutherland. n/a 
Reference(s):
none recorded or not applicable
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable