Sand intraclast development and the deformation of glacially-overridden permafrost, West Runton

Glacially‐deformed sediments have often been observed to contain masses of sorted sediment in which delicate sedimentary structures remain preserved. These features, variously termed “lenses”, “blocks”, “intraclasts” range in surface area from a few mm2 to many tens of m2 and when extensive lead to the development of “glacial mélanges” (e.g. Menzies, 1990a,b; Hoffman and Piotrowski, 2001). Various hypotheses have been proposed to account for the inclusion of sorted‐sediment masses within glacial tills. These include englacial meltwater deposition (Goodchild, 1875), basal freeze‐on and transport within a debris‐rich basal ice layer (e.g. Hoffman and Piotrowski, 2001) and entrainment and deformation within a subglacial deforming layer under both unfrozen (Rappol, 1987, Menzies 1990a) and partially frozen conditions (e.g. Menzies, 1990a; Waller et al., 2009; Waller et al., 2011). In spite of this previous research, their origin and significance remains the subject of debate, largely centering on the conditions required to explain the rheological contrasts inherent in glacial mélanges and the survival of cohesionless coarse‐grained intraclasts within a deforming medium (e.g. Menzies 1990a,b).