DEGLACIAL CHRONOLOGY IN COLD-BASED TERRAIN WITH IRSL SINGLE GRAIN DATING OF GLACIOLACUSTRINE DELTAIC SEDIMENTS ON BAFFIN ISLAND

In the cold-based glacial environments of the Arctic region, the timing of the retreat of the Laurentide ice sheet is of limited knowledge due to the scarcity of datable organic material, and abundance of inherited cosmogenic isotopes in available boulders. Here, we report the results of an extended infrared stimulated luminescence (IRSL) dating program conducted on feldspar single grains. The dated material is from glaciolacustrine deltas (GLD) of the mostly cold-based plateaus of southern Baffin Island. We obtained 12 IRSL ages, 11 on GLD and one from a glaciomarine delta. The dated material is composed of medium to coarse sand, taken at an average depth of 0.5 m (small shovel-dug pits) from the surface of the delta. A total of 6791 grains were measured, from which 2706 grains provided ages, amongst which 772 are considered as infinite (in other words, they were not bleached prior to deposition). Three samples were dated for each ice margin positions, allowing results cross-validation. The method of age determination from the distribution of single-grain ages is also discussed, where the minimum age model has been used in most cases. A finite mixture model analysis was conducted in one case, where the results appear to display a young age population, likely due to post-depositional reworking or contamination. The IRSL ages (bracketed between 6 and 8 ka CAL BP) show a good correlation with a chronology based on 14C (converted to calendar years) from post-glacial marine littoral shells and inland peat (from various authors, reported in Dyke, 2003). Comparisons were made with TCN dates tested on four boulders, yielding ages of ca. 14 ka or more, indicating inherited cosmogenic isotopes. Overall, the IRSL ages are consistent with a rapid deglaciation in the South Baffin Island area following the position marked by the Frobisher Bay moraine.