DETRITAL ZIRCON PROVENANCE OF CENOZOIC STRATA IN THE BEAUFORT-MACKENZIE BASIN, ARCTIC OCEAN, CANADA

The Beaufort-Mackenzie Basin consists of over 15 km of sedimentary strata that were deposited in the Arctic Ocean along the northwestern margin of Canada. Upper Cenozoic strata in the basin archive the evolution of high-latitude river systems, which is important for understanding the drivers behind drainage reorganization and temporal fluctuations in freshwater input to the Arctic Ocean. Despite its importance, no sediment provenance data are available from the Beaufort-Mackenzie Basin. We sampled well-cuttings of Oligocene to Pliocene strata from wells drilled in this basin and analyzed the sediments using detrital zircon U-Pb geochronology. The raw material available to sample is extremely limited (approximately 80 grams per 40 meters of strata); however, we were able to extract from these small samples a sufficient number of zircons for analyses. Zircons from the Oligocene Kugmalit and Mackenzie Bay formations have age populations with peaks at <250 Ma and 400 Ma, multiple peaks between ca. 1000 and 2000 Ma, and a peak at ca. 2600 Ma. The detrital zircon populations within the Oligocene strata are similar between wells and across stratigraphic sequences, indicating a relatively stable drainage pattern during this time interval. Zircons from the Pliocene-age Iperk Formation have ages that are similar to those from the underlying units, with age peaks at <250 Ma and 450 Ma, a population between 1000 and 2000 Ma, and a population centered at 2500 Ma. We compiled over 5000 zircon ages from rocks in northwestern Canada to better interpret sediment provenance. Based on similarities in zircon age populations, the Cenozoic sediment in the Beaufort-Mackenzie Basin are interpreted to have been derived from rocks exposed in the northern Canadian Cordillera. These data support previous hypotheses that propose two to three river system exited the northern Canadian Cordillera and emptied into the Beaufort-Mackenzie Basin. Changes to river patterns in northwestern Canada during the late Cenozoic will be discernible in the upper Cenozoic sedimentary record by changes to the dominant detrital zircon populations.