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

Abstract

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.

Marine Molluscs as Indicators of Environmental Change in Glaciated North America and Greenland During the Last 18 000 Years

“…Richard et al (in review) showed by AMS dating of macrofossils that previous conventional radiocarbon dates from the plateau of Gaspé Peninsula are too old and that déglaciation finally occurred after 10 ka BP rather than about 12 ka BP. Payette (1993) and Gray et al (1993) proposed that final déglaciation of the Ungava region of Québec occurred 5.5-5 ka BP, 1 ka later than the date suggested by Dyke and Prest (1987). The younger déglaciation proposal for that area is based on a few basal peat and gyttja dates that Dyke and Prest (1987) regarded as not closely constraining the dates of déglaciation and on a peculiarity in the present distribution of Larix.…”

“…A sample placed well inside the ice margin in Hudson Strait consists of unidentified shell fragments from till on Akpatok Island dated at 11.97 ka BP. These apparently record a brief opening of the strait followed by a readvance of ice onto southern Baffin Island (Gray et al, 1993). Foraminiferal and diatom records of cores off Hudson Strait indicate fairly high biological productivity and seasonally open water 12-11 ka BP (Andrews era/., 1990).…”

Émersion des terres et développement des sols bien drainés au lac Guillaume-Delisle, Québec subarctique

“…Les courbes d'émersion disponibles pour le Québec nordique reposent surtout sur la datation de coquillages marins et peu sur des datations de sols enfouis (Gray et al, 1993). Les environnements littoraux sableux récents du lac Guillaume-Delisle sont cependant pauvres en coquillages marins et la courbe d'émersion des terres est basée principalement sur des datations de coquillages, toutes plus anciennes que 4500 années cal.…”

La composition isotopique des mollusques marins et sa relation à la déglaciation de la péninsule d’Ungava

“…Les mollusques analysés sont issus des sédiments marins de la péninsule d'Ungava et des îles adjacentes dont l'exondation glacio-isostatique pendant l'Holocène a été étu-diée par Gray et al (1993). L'objectif était d'établir des courbes d'émersion.…”

“…Les échantillons de mollusques dont les âges et les valeurs en 8 PDB ' 8 Oont été déterminés furent récoltés au cours des vingt dernières années dans le cadre des recherches sur ! 'emersion postglaciaire de cette région (Gray et al, 1993). Quelques données isotopiques ont déjà été publiées, notamment celles provenant de la côte ouest de la baie d'Ungava (Lauriol et al, 1979 ;Gray et al, 1980).…”