Ground-ice stratigraphy and formation at North Head, Tuktoyaktuk Coastlands, western Arctic Canada: a product of glacier-permafrost interactions

Glacially deformed permafrost at North Head, in the Tuktoyaktuk Coastlands of western Arctic Canada, contains a complex ground-ice stratigraphy that formed during the course of the last glacial–interglacial cycle. Two generations of ground ice are distinguished within a single stratigraphic sequence. Pre-deformation ice has been glacially deformed or eroded beneath the cold-based margin of the Laurentide Ice Sheet (LIS) during Marine Isotope Stage 2. Such ice comprises (1) buried basal ice, (2) massive segregated ice and (3) ice clasts subglacially eroded from pre-existing ground ice. In contrast, post-deformation ice has not been glacially disturbed because it formed during or after deglaciation; it includes (4) dykes and sills of intrusive ice, (5) massive segregated-intrusive ice, (6) ice wedges and composite wedges, (7) segregated ice and (8) pool ice. The superimposition of post-deformation intrusive ice and massive segregated-intrusive ice into permafrost containing pre-deformation ground ice indicates that substantial quantities of overpressurized water were injected into ice-marginal permafrost during or after deglaciation. The required external water source for the post-deformation intrusive ice was probably overpressurized subpermafrost groundwater in front of the retreating margin of the LIS. Injection of this water into proglacial permafrost hydraulically fractured the permafrost and formed ice dykes, ice sills and massive segregated-intrusive ice. A two-stage model of massive-ice development can be reconciled with known permafrost and glacial conditions in the ice-marginal context of the Late Wisconsinan LIS. The model probably applies to some other glaciated terrains of the western Canadian Arctic.