Sand and sand-ice fillings of Quaternary thermal contraction cracks on Summer and Hadwen Islands, Western Arctic Canada, comprise sand veins, sand wedges, and composite wedges. Sand wedges in diamicton-poor ice, diamicton-rich ice, and ice-rich sand generally have simple V shapes, whereas those in ice-poor sand vary from V-shaped to irregular forms and may contain inclusions of host sand. These morphological differences are explained in terms of the relative tensile strength of the wedge and host materials. Bundles of sand veins within sand wedges indicate discrete stages of wedge growth. Criteria previously proposed for identifying relict sand wedges are reevaluated: (1) Not all wedges are V.shaped; some are irregular forms with offshoot sand veins. (2) A vertical or steeply dipping lamination is not apparent within all wedges; some appear to have a massive fill, suggesting that the sand source can be texturally and mineralogically very uniform. (3) Individual sand veins and groups of veins can be just as common within sandy host materials as the better-known sand wedges. Composite sand-ice wedges at Crumbling Point, Summer Island, commenced growth as composite wedges, continued as sand wedges, were modified by thermokarst, and, in some cases, recommenced at a stratigraphically higher level as ice wedges. The sand-wedge and ice-wedge stages reflect environmental change from cold, arid, and windy proglacial conditions during Oxygen Isotope Stage 2 to warmer and wetter interglacial conditions during OI Stage 1.

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