Dynamics of the Late Wisconsin Ice Sheet in the Ungava Peninsula Interpreted from Geomorphological Evidence

Abstract

Radiocarbon evidence, isostatic uplift data, and glacial landforms in the Ungava Peninsula have provided important insight into the nature and dispersal pattern of the late Wisconsin ice sheets in northeastern Canada. A shell date of 37,000 + 400 BP from the Hudson Strait coast of Ungava indicates that at least the coastal area of Ungava may have been deglaciated during the last glacial period. Subsequently, an ice sheet developed over the entire peninsula, leaving, as a heritage, a symmetrical sequence of landform assemblages. The latter, along with striae, flutings, and drumlinoid features, indicate radial flow of the ice sheet towards Hudson Bay, Hudson Strait, and Ungava Bay from a dispersal center in the interior. The ice sheet may have been cold-based in the vicinity of the ice divide, becoming warm-based towards its margins. A thick unmoulded till plain, situated along the ice divide, is speculatively thought to be inherited from beneath an earlier and thicker ice sheet. The earliest withdrawal of late Wisconsin ice inland from the coastal regions took place ca. 10,000 BP in the Rivière Déception-Cap de la Nouvelle-France area in northeastern Ungava. Locally high marine limits on the offshore islands in the vicinity support the concept of ice withdrawal to a stable position inland on the Ungava plateau. By 8000 BP the entire Hudson Strait coast and the northwestern part of Ungava Bay were ice free. The ice front was actively calving inland from Hudson Bay. An important lobe of central Quebec-Labrador ice probably filled southern Ungava Bay until as late as 6500 to 7000 BP, accounting for the existence of glacial lakes in the valleys of several of its tributary rivers, and possibly a negative gravity anomaly in the same region. Marine-limit elevations suggest that the Ungava ice sheet resulted in equivalent glacial loading on both the Hudson and Ungava Bay coasts, and that the thickest ice masses were situated to the south of the Ungava Peninsula along the axis between southeastern Hudson Bay and central Quebec-Labrador.