A REFINED DEGLACIAL CHRONOLOGY AND IMPLICATIONS TO THEORIES OF THE PEOPLING OF THE AMERICAS

A refined chronology of deglaciation for the western Laurentide Ice Sheet (LIS) has been elusive for many reasons. Datable material in lakes has shown to produce unreliable dates due to contamination, or because of time for succession to produce organics. Other factors relate to the fact that deglacial landforms cannot be directly dated, and that landforms identified as deglacial moraines have been misidentified. Since the purported "Ice-Free Corridor" has been demonstrated to have been full of ice during glacial maximum, it becomes crucial to refine the deglacial chronology to see if the interior route was a tenable option for migration of the first peoples into the Americas.

We identified a shallow gravel braidplain on a high surface in the Wapiti drainage in west-central Alberta, near the zone of interaction between the Cordilleran and Laurentide ice sheets. The plain would have been formed during a stage of Glacial Lake Peace, that was dammed by a proximal Laurentide Ice Sheet (LIS). Two horse bones, discovered 50 km apart in the gravel plain yielded radiocarbon dates in the 11,200-11,400 age range, thereby dating the deposition of the braidplain and the location of the LIS. Those dates suggest that the LIS persisted in the area somewhat later than originally thought. This suggests that a migration from the north at this time would have been challenging as ice and very large proglacial lakes persisted until about 11,000 radiocarbon years B.P. Sites far to the south that are significantly older likely saw migration originate from a different location, or time.