Écoulements glaciaires et déglaciation hâtive (ca 11 ka Bp ?) du nord-est de la péninsule d'Ungava, Québec, Canada

Abstract

Studies of the lithological composition and carbonate contents in the till, the glacial striations and the glacial geomorphology allowed the identification of two distinct ice flows at the northeast end of the Ungava Peninsula and in the area of the Hudson Strait. A general northeastward ice flow, from the Ungava Plateau, has marked the overall region. It joined to an eastward ice stream occupying the Hudson Strait that left traces on Charles Island. This ice stream evacuated the Foxe Basin and the Hudson Bay and overlapped to a limited extend the head of the Ungava Peninsula at Cape Nouvelle-France. The thinness of the till associated with the Ungava flow, the presence of perched blocks among which some are pedestal, and the lack of tapered forms suggest the presence of a ice with low content of debris and cold base in some areas. Subsequently to the westward glacial recession from the Hudson Strait, a readvance of the Ungava glacier with northeast-north direction intersected the earlier eastward movement and calved in the strait at the North of Charles Island. New 14C dating by accelerator mass spectrometry on marine mollusks permitted to locate the deglaciation of the plateau margin, between Deception Bay and Cape Nouvelle-France, prior to 8.5 ka BP. Many older dates suggest the possibility of a very early opening of the Hudson Strait, as early as 10.5–11 ka BP. The early deglaciation in some areas could explain the very high levels of the marine limit of the transgression observed at Cape Nouvelle-France. Furthermore, many ages are intersecting the interval of 8.4–8.9 ka BP, making suspicious the chronology of the glacial readvance of Noble Inlet across the Hudson Strait to the east.