SUBGLACIAL AND SUBAQUEOUS PROCESSES NEAR A GLACIER GROUNDING LINE - SEDIMENTOLOGICAL EVIDENCE FROM A FORMER ICE-DAMMED LAKE, ACHNASHEEN SCOTLAND

Subglacial and subaqueous sediments deposited near the margin of a Lat e-glacial ice-dammed lake near Achnasheen, northern Scotland, are desc ribed and interpreted. The subglacial sediments consist of deformation tills and glacitectonites derived from pre-existing glaciolacustrine deposits, and the subaqueous sediments consist of ice-proximal outwash and sediment flow deposits, and distal turbidites. Sediment was deliv ered from the glacier to the lake by two main processes: (1) subglacia l till deformation, which fed debris flows at the grounding line; and (2) meltwater transport, which fed sediment-gravity Bows on prograding outwash fans. Beyond the ice-marginal environment, deposition was fro m turbidity currents, ice-rafting and settling of suspended sediments. The exposures support the conclusion that the presence of a subglacia l deforming layer can exert an important influence on sedimentation at the grounding lines of calving glaciers.