U-Pb Detrital Zircon Geochronology of the Jurassic through Lower Cretaceous Strata of the Rocky Mountains, Southwestern Alberta

U-Pb detrital zircon geochronology from Lower Jurassic to Lower Cretaceous strata of the southern Canadian Rocky Mountains fold-thrust belt documents the presence of detrital zircons with ages close to the time of sediment accumulation throughout this succession. This indicates that the drainage systems that discharged into the local expression of the Western Interior Seaway were accessing western contemporaneous igneous sources in the Cordillera from at least the Early Jurassic, long before the Kimmeridgian initiation of the foredeep trough. Older grains in the Jurassic strata reflect the pre-history of the basin distributive province and show an episodic pattern that includes well-defined lower Paleozoic and Grenvillian maxima, and Paleo- to early Neoproterozoic populations, which may reflect recycling of detrital zircons from older clastic formations uplifted in the eastern part of the orogen, or less likely, eastern sources. Maximum depositional ages constrained by the youngest detrital zircons in the analyzed stratigraphic units are: Sinemurian for the Jurassic Basal sandstone (however, this unit is diachronous in the basin), Pliensbachian for the Poker Chip Shale, late Aalenian for the Rock Creek Member, Bathonian for the Gryphaea Bed, Tithonian for the uppermost Passage Beds and Aptian for the Cadomin Formation.