Postglacial emergence of Ungava Peninsula, and its relationship to glacial history

• Published in: Canadian Journal of Earth Sciences
• Main Authors: Gray, James, Lauriol, Bernard, Bruneau, Denis, Ricard, Jean
• Format: Article in Journal/Newspaper
• Language: French
• Published: Canadian Science Publishing 1993
• Subjects: General Earth and Planetary Sciences; Hudson Bay; Hudson Strait; Ice Sheet; Inukjuak; Resolution Island; Ungava Bay; Ungava peninsula
• Online Access: http://dx.doi.org/10.1139/e93-147; http://www.nrcresearchpress.com/doi/pdf/10.1139/e93-147

A series of 178 radiocarbon dates, of late glacial and postglacial age, from raised marine terraces on the Hudson Strait, Hudson Bay, and Ungava Bay coasts, permit a new synthesis of deglaciation history, postglacial emergence, and glacio-isostatic recovery of the Ungava Peninsula. Marine limits show three local highs, related to centres of ice loading: east of Hudson Bay; southwest of Ungava Bay, and in western Hudson Strait. Eastward extension of the latter to Cap de Nouvelle-France is attributed to early deglaciation. Emergence curves are presented from 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 variations in rates of ice sheet unloading, immediately after coastal deglaciation. A stable onshore ice margin kept the northeastern tip of Ungava isostatically depressed, from initial deglaciation until 7 ka, whereas 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 marine and glacial lake shoreline data, indicate maximum ice loading centres in eastern Hudson Bay and in central Quebec–Labrador, with an extension 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 high tide gauge values. A downward gradient of 6.5 ka isobases in a northeasterly direction from southeastern Ungava towards present sea level on southern Resolution Island at the mouth of Hudson Strait suggests that Ungava Bay, despite late occupation by glacial ice, was probably not a major loading centre.