PRELIMINARY DETRITAL ZIRCON PROVENANCE DATA FROM CENOZOIC STRATA IN THE BEAUFORT-MACKENZIE BASIN, ARCTIC CANADA

The Mackenzie River of western Canada flows northward into the Beaufort-Mackenzie Basin, delivering large volumes of sediment, nutrients and freshwater to the Arctic margin of Canada and impacting a number of regional and global systems. Throughout most of the past 50 million years, freshwater runoff in western Canada was routed eastward through the Bell River System, with only local rivers emptying into the Beaufort-Mackenzie Basin. However, at some point in the last ca. 10 million years this pattern changed and the Mackenzie River drainage basin was established. The timing, cause and potential effects of this drainage reorganization remain unknown, although sedimentation rates in the basin increase by 2000% during the Pliocene, suggesting a change in the sedimentary systems. To better understand sediment provenance in the Beaufort-Mackenzie Basin and the evolution of paleodrainages in northwestern Canada we collected samples from Oligocene-Pleistocene strata for detrital zircon U-Pb geochronology. Oligocene strata of the Kugmallit sequence contain large populations with Paleozoic and Proterozoic ages, with peaks at ca. 400 Ma, 1200 Ma and 1800 Ma. These data are interpreted as recording sediment derived primarily from the northern Canadian Cordillera via local river systems during the Oligocene and provide a baseline for comparison to younger strata. We anticipate that overlying strata, particularly the Pleistocene Iperk sequence will contain greater proportions of Archean-age zircons reflecting greater input from the Canadian Shield. Combined with improved chronostratigraphic constraints, these data will help constrain the timing of drainage basin changes in northwestern North America, which in turn will inform paleoclimate models and can be used to evaluate proposed forcing mechanisms.