POSTGLACIAL EMERGENCE OF UNGAVA PENINSULA, AND ITS RELATIONSHIP TO GLACIAL HISTORY

A series of 178 radiocarbon dates, of late glacial and postglacial age , from raised marine terraces on the Hudson Strait, Hudson Bay, and Un gava Bay coasts, permit a new synthesis of deglaciation history, postg lacial emergence, and glacioisostatic recovery of the Ungava Peninsula . Marine limits show three local highs, related to centres of ice load ing: east of Hudson Bay; southwest of Ungava Bay, and in western Hudso n Strait. Eastward extension of the latter to Cap de Nouvelle-France i s attributed to early deglaciation. Emergence curves are presented fro m sites in (1) Hudson Strait ice-free prior to 9 ka; (2) Hudson Strait ; (3) Hudson Bay; and (4) Ungava Bay liberated by Ungava ice between 8 and 6 ka. A sigmoidal pattern for the first group, with slow initial emergence, contrasts markedly with a pattern of rapid deceleration of emergence for the other groups. These differences are attributed to va riations in rates of ice sheet unloading, immediately after coastal de glaciation. A stable onshore ice margin kept the northeastern tip of U ngava isostatically depressed, from initial deglaciation until 7 ka, w hereas other mainland coasts were only liberated by retreat of the ice margin during a final phase of rapid thinning of the continental ice sheet. Isobases on emergence since 6.5, 5, and 2 ka, derived from mari ne and glacial lake shoreline data, indicate maximum ice loading centr es in eastern Hudson Bay and in central Quebec-Labrador, with an exten sion northwards towards Ungava Bay. An uplift rate of 14 mm/year since 2 ka for Inukjuak on the Hudson Bay coast is compatible with very hig h tide gauge values. A downward gradient of 6.5 ka isobases in a north easterly direction from southeastern Ungava towards present sea level on southern Resolution Island at the mouth of Hudson Strait suggests t hat Ungava Bay, despite late occupation by glacial ice, was probably n ot a major loading centre.