Early Holocene glacial lakes and ice marginal retreat pattern in Labrador/Ungava, Canada

Abstract

The existence of glacial lakes Naskaupi, McLean, Minto, Mélèzes, and Wapussakatoo during the deglaciation of Labrador/Ungava, Canada, was recognized at the end of 1950s. However, glacial lakes have seldom been included in regional reconstructions to constrain the outline of successive ice margins during the glacial retreat in Labrador/Ungava. Reconstruction of the ice flow succession in Labrador/Ungava has often primarily focused on till lineation systems. These reconstructions often depict a late glacial ice dispersal center situated over central Labrador/Ungava. More recent studies on glacial geomorphology including meltwater features, however, suggest that north-central Labrador/Ungava exhibited cold-based conditions at least during the latest deglaciation. Cold-based conditions inhibit basal sliding and formation of landforms, except for meltwater traces such as meltwater channels, glacial lake shorelines and deltas. This situation implies that meltwater traces are the main source of information when reconstructing the spatial retreat pattern during a cold-based deglaciation. Evidence presented in this study, such as glacial lake shorelines, fossil deltas, and spillway and drainage channels in north-central Labrador/Ungava, indicates the existence of numerous previously unmapped glacial lakes. The mapped glacial lake features are synthesized to a reconstruction of several glacial lake stages which, in turn, are used to constrain the late glacial ice margin retreat pattern over the inferred cold-based areas of north-central Labrador/Ungava. A total of 26 glacial lakes (65 sub-stages) existed during the deglaciation of Labrador/Ungava. These lakes were impounded along the southern margin of the shrinking ice sheet. The required damming ice margins indicate that the last ice remnant of the Laurentide Ice Sheet in Labrador/Ungava was situated over the southern Ungava Bay and the adjacent southern shore.