Configuration and timing of the postglacial marine incursion along the eastern Ungava Peninsula (Nunavik, Canada): implications for deglaciation models

The final deglaciation stages of the Laurentide Ice Sheet in northern Quebec–Labrador were marked by the incursion of the d'Iberville Sea into the coastal areas of Ungava Bay. Remote and field mapping of raised marine strandlines along the Ungava Peninsula east coast show that the maximum marine limit decreases from south (165 m) to north (100 m), reflecting differential uplift linked to an ice mass remnant located to the southwest of the bay. Reconstruction of the uppermost marine limit in two east–west transects extending into the Peninsula interior reveals distinct sea-level stands with limited extents towards the west, indicating that the early stages of the marine incursion occurred in contact with the ice margin. The reconstruction also identifies the maximum eastward extent of ice-dammed lakes that occupied the Arnaud River and Aux-Feuilles River valleys. ¹⁰Be surface exposure dating of marine strandlines yielded consistent ¹⁰Be ages that indicate a rapid deglaciation of Ungava Bay between 8900 ± 200 a (north) and 7900 ± 200 a (south). These results provide constraints on the position of the Labrador Sector eastern and western ice margins during the late deglaciation, in addition to the timing of ice and meltwater discharges from the Ungava Bay region.