Géologie du Quaternaire du nord de la péninsule d'Ungava, Québec

During the last glaciation, a lengthy ice-flow phase in the northern part of the Ungava Peninsula was associated with the presence of an ice divide that extended along a northwest-southeast axis between Ivujivik and Lake Nantais and represented the northern extension of the New-Quebec ice divide. This major ice-flow phase was preceded by two others, the first associated with radial ice flow from a dispersal centre north of the Monts de Puvirnituq (Ungava flow), and the second, with flow that moved outward on the peninsula from a dispersal centre farther south, probably corresponding to the Payne dispersal centre. The overall dispersal of rock debris from the Cape Smith Belt can be linked to the major phase of ice flow, with ice flowing outward on the peninsula on either side of the ice divide. Glacial transport distance also increases with increasing distance from the ice divide. Moreover, the presence of Paleozoic carbonate rocks in till on Charles, Maiden, and Wales islands and locally on the mainland between Cap de Nouvelle-France and Douglas Harbour, as well as the relative ice-flow chronology inferred on Charles Island, indicate that before the major ice-flow phase, a northeast-flowing ice stream had formed in Hudson Strait in this area, to the east of the New-Quebec ice divide. Deglaciation began between 10 700 and 9000 BP and was almost complete shortly after 7000 BP. A diachronous marine invasion accompanied the retreat of the ice margin, firstly along the edge of Hudson Strait and then along Hudson Bay. The marine limit reached its highest elevation (about 180 m) in the Hudson Strait area and its lowest (about 110 m), in the Hudson Bay area. The orientation of eskers and marginal meltwater channels and the evidence of proglacial lakes suggest that the ice margin retreated toward the west-central part of the peninsula, to an area slightly west of the ice divide. Proglacial lakes, trapped between the receding ice margin and the highlands to the north and northeast, occupied primarily three watersheds, the Puvirnituq River basin (549 to 230 m), the Kovik River basin (396 to 213 m), and the basin formed by the Frichet, Derville, and Durouvray rivers (439 to 132 m). Approximately 30% of the area was covered by one or another of these proglacial lakes, whose levels dropped steadily as their lowest outlets were deglaciated.