An assessment of fluting and till esker formation on the foreland of Sandfellsjokull, Iceland

Intensive sedimentological analysis of tills, parallel-sided flutings, and a conduit fill (till esker) on the recently deglaciated foreland of Sandfellsjokull (a temperate, actively receding piedmont lobe draining the eastern margin of the Myrdalsjokull ice cap in southern Iceland) reveals that subglacial sediment was emplaced predominantly as a dilatant A horizon after an initial phase of glacitectonite production from local outwash. Clast macrofabric strengths weakened through time, presumably in response to increasingly wetter substrate conditions, until the emplacement of the fluted till when clast alignment was more tightly constrained. The fluting phase was initiated only after boulders were plucked from an adjacent bedrock cliff and lodged at the ice-till interface. This suggests that the parallel-sided flutings constrained shearing at the ice-bed interface in a similar fashion to a fault gouge, thereby strengthening clast alignments but allowing the till to mould around larger obstacles to produce herringbone fabric patterns. Strong clast macrofabric strengths in the till esker are not parallel to the ice flow direction, but instead align parallel with the local axis of the meandering ridge. This suggests that the till esker was likely produced by the squeezing of a dilatant till into an elongated cavity or R-channel after meltwater evacuation, followed by localized deformation, constrained by the channel walls, as the channel moved downvalley because of ice flow. The short period over which the deformation took place was enough to impart weaker fabrics in parts of the conduit that lie transverse to the ice flow direction and stronger fabrics where the conduit trends toward parallelism with the ice flow. (C) 2009 Elsevier B.V. All rights reserved.