Submarginal erosion

Blocks of ice up to 15m long and 1.5 m high, some folded, are dispersed throughout the glaciotectonite (Fig. 64.2B). Where bands in the ice blocks are truncated along the margins of the blocks, in situ formation of segregated or intrusive ice is discounted. Instead the ice was eroded from pre-existing ice and thus represents ice clasts. Submarginal erosion of ice also explains the occurrence of an angular unconformity along the top of the

Figure 64.1 Photomontage and structural interpretation of the section through the moraine complex at the Leverett Glacier. Numbered arrows show the location of the key units, thick black lines delineate their boundaries, and thin white lines highlight the orientation and extent of structures within them. Ice flow was from left to right.

Figure 64.1 Photomontage and structural interpretation of the section through the moraine complex at the Leverett Glacier. Numbered arrows show the location of the key units, thick black lines delineate their boundaries, and thin white lines highlight the orientation and extent of structures within them. Ice flow was from left to right.

Figure 64.2 Structures reflecting glacier-permafrost interactions in western Arctic Canada: (A) pinch-and-swell structure of sand, North Head (trowel for scale) (69°43'N, 134°26'W); (B) ice clasts within glaciotectonite, Pullen Island (area depicted ca. 1.5m wide) (69°46'N, 134°25'W); (C) buried basal ice, Mason Bay (face is ca. 4m high) (69°33'N, 134°02'W); (D) ice dyke-sill truncating a composite wedge, North Head (spade for scale).

Figure 64.2 Structures reflecting glacier-permafrost interactions in western Arctic Canada: (A) pinch-and-swell structure of sand, North Head (trowel for scale) (69°43'N, 134°26'W); (B) ice clasts within glaciotectonite, Pullen Island (area depicted ca. 1.5m wide) (69°46'N, 134°25'W); (C) buried basal ice, Mason Bay (face is ca. 4m high) (69°33'N, 134°02'W); (D) ice dyke-sill truncating a composite wedge, North Head (spade for scale).

underlying massive ice. Had the unconformity resulted from downward thaw, then the ice clasts above it would have thawed. Preservation of the ice clasts and the underlying massive ice indicates that erosion occurred at subfreezing temperatures.

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