PALEODRAINAGE OF THE LOWER CRETACEOUS MCMURRAY FORMATION, EASTERN MARGINS OF THE ALBERTA FORELAND BASIN SYSTEM

The Aptian McMurray Formation in the eastern Alberta foreland basin, consists of basal fluvial deposits that become increasingly marine-influenced upwards. This presentation examines the McMurray drainage area and sediment-routing system within the context of the evolving foreland basin. A large body of detrital-zircon (DZ) data indicate the McMurray was the axial stream for a drainage sourced in the Appalachian Cordillera of the southeastern US through eastern Canada, which served as the divide between the Gulf of Mexico-Atlantic and the Boreal Sea. This continental-scale drainage is hypothesized to have been routed through the US midcontinent, and it was a contributive system, joined by shield-derived tributaries from the east, and Sevier fold and thrust belt tributaries from the southwestern US. The position of the McMurray axial drainage is consistent with the broad low-relief backbulge of the Cordilleran foreland basin, with the forebulge represented by the area of thin McMurray deposition to the west. The McMurray paleodrainage is interpreted to represent the last vestiges of continental-scale east-to-west sediment transfer derived from development of the Paleozoic Appalachian Cordillera along the eastern margin of North America.

Several samples from the hypothesized US midcontinent contributing area were collected to further test these interpretations. These include basal Cretaceous samples from the Colorado Front Range, where paleocurrents show flow to the east-northeast, and DZ data indicate a source terrain in the Sevier fold and thrust belt in the southwestern US. Additionally, basal Cretaceous samples in Kansas, Nebraska, and South Dakota show paleocurrents flowing west-northwest, and DZs that indicate an Appalachian source. These data compile to show east- and west-flowing drainages that converge to flow north in the backbulge of the foreland basin system in the US. This system is interpreted to represent the feeder system for the McMurray Formation, which represents the Mississippi or Amazon of its time.