ATHABASCA OIL SANDS, ALBERTA, CANADA: WHENCE THE SAND?

Northeastern Alberta’s Athabasca Oil Sands represent one of the largest hydrocarbon accumulations in the world. The Lower Cretaceous McMurray Formation is the principal bitumen reservoir, and despite its economic and political importance, the provenance and sediment transport history of this unit remains unclear. Petrographic evidence suggests much of the sand was derived from the Canadian Shield, however early paleogeographic reconstructions imply a continental scale, south-to-north drainage network originating in the southwestern United States.

This research uses U-Pb detrital zircon geochronology to better understand sediment transport pathways and depositional history. Nine samples taken from three cored wells displayed three distinct detrital zircon signatures, which form the basis of three chronofacies. Chronofacies (i) contains zircons of Archean (ca. 2800-2600 Ma) and Early Proterozoic age (ca. 1900-1800 Ma). These are interpreted to have been derived from the Superior and Trans-Hudson age belts of the Canadian Shield. Chronofacies (ii) is dominated by zircons of Late Proterozoic (ca. 1250-950 Ma) and Early Paleozoic age (ca. 600-350 Ma), which suggests a Grenville and Appalachian source, respectively. However, these zircons may be multi-cyclic; originally transported from the Appalachians, deposited in the southwestern United States or southern Canada, and subsequently transported to the study area in the Early Cretaceous. Chronofacies (iii) is characterized by relatively young zircons (<250 Ma) and a lesser population of Early Proterozoic ages (ca. 1900-1800 Ma), and are interpreted to indicate a Cordilleran provenance. These disparate signatures suggest a complex provenance history that evolved throughout McMurray deposition.

To further constrain provenance, we are using paleochannel dimensions of the McMurray Formation to estimate paleodrainage basin sizes, employing modern geomorphological parameters and relationships. This information will enable more critical assessments of the current working hypotheses.