Geomorphic and ecological age constraints for paraglacial to non-glacial transition in northeastern British Columbia, Canada

Abstract

The Late Wisconsinan deglaciation period was a time of rapid climate adjustment that resulted in the widespread transition from proglacial/paraglacial conditions to non-glacial settings favourable for plant and animal colonization. Establishing the timing of this transitional period in northeastern British Columbia provides constraints on the rate in which the biomes adapted during this interval of rapid climate change.Preserved aeolian landforms (geomorphic) and macrofossil assemblages (biological) are complementary proxies for interpreting climate amelioration. Paraglacial aeolian dunes in the Kiskatinaw dune field developed following the retreat of glacial Lake Peace which formed after the separation of the Cordilleran and Laurentide ice sheets. These parabolic sand dunes are vegetation-anchored landforms that indicate plant colonization bio-morphologically influenced aeolian activity during stabilization. Optical dating established that stabilization occurred about 10.8 ± 0.3 ka ago (weighted mean of six ages), around the same time interval in which vegetation transitioned from herb and shrub tundra to forest tundra, then to a boreal parkland. Radiocarbon ages from macrofossil assemblages at the Flatbed River section infer paraglacial conditions likely persisted to around 12 000 cal yrs BP and the site had characteristics of a forest tundra. At that time, the Flatbed River was a dry floodplain that transitioned to a pond setting in a boreal parkland after 12 447–11 941 cal yrs BP and before 11 690–11 279 cal yrs BP. The site transitioned from pond to bog after 10 149–9771 cal yrs BP, coincident with the onset of boreal forest conditions that were established by 9901–9607 cal yrs BP.Biome succession recorded at the Flatbed River section and the stabilization of sand dunes indicates that the site transitioned from a paraglacial setting associated with tundra to a non-glacial setting characterized by a boreal forest environment over approximately 2 ka (ca. 12.0–9.7 ka ago). However, the change from tundra to parkland forest conditions took <500 years (ca. 12.0–11.5 ka ago). This suggests that climate warming enabled a rapid transition from cold dry tundra to parkland forests in as little time as few centuries.