Appalachia to Athabasca: Reconstructing the Early Cretaceous Continental Paleodrainage System Associated with the Oil Sands of the McMurray Formation, Alberta, Canada
The Athabasca Oil Sands of northeastern Alberta host one of the largest reserves of hydrocarbons in the world. Of these deposits, the Lower Cretaceous (Aptian) McMurray Formation is one of the principal reservoir sandstones in the region. The provenance of these sandstones, and the corresponding Early Cretaceous paleodrainage system in the region remain poorly constrained. Heavy mineral and petrographic data suggest the sediment was derived from the nearby Canadian Shield, whereas paleogeographic maps commonly show the sediment coming from areas to the south, possibly as far away as the Colorado Plateau. This study examines the detrital zircon provenance of sandstones from the McMurray Formation and surrounding units to constrain paleodrainage patterns, define sediment distribution networks, and better predict reservoir characteristics. We sampled nine sandstone samples from wells in the McMurray Formation and several outcrop samples from surrounding Lower Cretaceous units and analyzed these using detrital zircon uranium-lead geochronology. Results indicate three distinct detrital zircon signatures within the McMurray Formation. The first signature is characterized by zircons of Archean and Early Proterozoic age, which are interpreted as indicating the sediment was derived from the Canadian Shield. The second signature is characterized by zircons of Grenville (ca. 1000 Ma) and early Paleozoic age. This zircon population suggests an Appalachian source originally. Although these zircons may have been derived directly from the Appalachians in the east, it is also possible this sediment was reworked from deposits in southern Canada or from the U.S. The third signature is dominated by relatively young zircons (<300 Ma) with a lesser population of Early Proterozoic ages, which are interpreted to indicate a Cordilleran provenance. These three signatures suggest a complex provenance history and one that evolved through time. First-order calculations based on fluvial channel dimensions and deposits provide important constraints on the location and extent of the paleowatershed. Ongoing analyses will improve provenance reconstructions and provide a more refined sedimentary history.
AAPG Datapages/Search and Discovery Article #90189 © 2014 AAPG Annual Convention and Exhibition, Houston, Texas, USA, April 6–9, 2014