DUNE FIELD FORMATION AND EVOLUTION ON THE NORTHERN GREAT PLAINS, CANADA

With more than 120 dune fields in Alberta, Saskatchewan and Manitoba, sand dunes are common features of the northern Great Plains of Canada. Most of these dunes are derived from sandy glaciofluvial or glaciolacustrine deposits, which represent finite sediment supplies that are not renewed through time. Initial dune formation probably closely followed deglaciation and drainage along the Laurentide and Cordilleran ice sheets, being time-transgressive from southwest to northeast. The present-day landscapes are the result of late Wisconsin post-glacial eolian activity and successive episodes of Holocene dune reactivation. Therefore, the morphology, orientation, stratigraphy and extent of past and present activity across the region must be interpreted with the recognition that many of these dune fields are complex “palimpsest” representations of past eolian activity.

Well-preserved, relict post-glacial dunes, dating between 17 000 and 11 000 years ago, are found only within the boreal forest regions of central Alberta and Saskatchewan, north of approximately 53 N latitude. Mid-Holocene dune deposits, dating between 6700 and 5000 years ago, are presently found within the parkland and southern boreal forest regions and overlie earlier post-glacial dune deposits in some areas. In the grassland region of the prairies, only the latter portion of this mid-Holocene dune record appears to be preserved, dating between 5600 and 4500 years ago. This suggests that intensive mid-Holocene dune activity may have reworked any earlier deposits in this region. Throughout most of the grasslands, late Holocene dune activity and stability, dating to between 5000 and 500 years ago, is also recorded in eolian deposits and is indicative of successive episodes of dune reactivation. In the driest, southwestern portions of Saskatchewan and southeastern Alberta, preserved dune deposits date mainly within the last 500 years, suggesting that recent episodes of aridity or other disturbances have caused the reworking of older deposits in the most arid portions of the prairies. Past wind directions, and other variables derived from the morphology and stratigraphy of dune fields, must be interpreted with an understanding of the complex eolian history of this region.