Early Cretaceous continental-scale sediment routing, the McMurray Formation, Western Canada Sedimentary Basin, Alberta, Canada

Alternative depositional models for the Early Cretaceous McMurray Formation between a dominantly continental and marginal marine settings remain a controversial topic. The source-to-sink model can be inverted to reconstruct ancient sediment-routing systems by utilizing methods to estimate ancient drainage basins, which can contribute to understanding of sediment routing and testing of alternative depositional models. New detrital zircon U-Pb ages from 31 samples were analyzed to identify source terranes of the McMurray Formation and the overlying Wabiskaw Member of the Clearwater Formation to test first-generation alternative sediment-routing models and estimate maximum depositional ages. In total, 9729 new concordant U-Pb ages identified multiple source terranes for the McMurray Formation within an interpreted continental-scale paleodrainage basin that extended from the SW to SE United States and eastern Canada. The paleodrainage basin then expanded to include the Western Cordillera arc system within the overlying Upper Mannville Group. Multidimensional scaling and mixing models independently support a paleo-upstream mixing of primary and recycled sources in the McMurray Formation axial system in the United States and a paleodownstream confluence between this axial system and east-derived sediment-routing systems in Canada, which display an evolution from bedrock-confined to alluvial morphology from the lower to middle-upper McMurray Formation. The current dataset constrains the maximum depositional age of the McMurray Formation to the latest Barremian to Aptian, with an age range from ca. 122 to 115 Ma, which is significantly younger than previously reported. Age estimates in the overlying Upper Mannville units from ca. 115 to 110 Ma statistically overlap with the McMurray Formation age, suggesting continuous Mannville deposition that lasted 10-12 m.y. or less.

Automated summary

Alternative depositional models for the Early Cretaceous McMurray Formation are controversial. New detrital zircon U-Pb ages from 31 samples were analyzed to identify source terranes and estimate maximum depositional ages. The results indicate multiple source terranes within a paleodrainage basin and support the mixing of primary and recycled sources in the axial system of the McMurray Formation. The maximum depositional age of the McMurray Formation is estimated to be significantly younger than previously reported.