Direct Correlation of Orogenic Pulses in the Southern Canadian Rocky Mountains Fold-and-Thrust Belt and Depositional Changes in the Adjacent Foreland Basin

Abstract

The Cordilleran foreland system in southern Canada evolved between the Middle Jurassic and early Eocene. New radiometric ages from regionally distributed thrust-fault gouge allow for the first time a direct correlation between the timing of intermittent eastward propagation of the southern Rocky Mountain foreland fold-and-thrust belt and the changes in the depositional processes and sediment input in the adjacent foreland basin to the east. In the Main Ranges, the Pyramid (163.0 Ma), Simpson Pass (161.7 Ma), and Johnson Creek (145.7 Ma) thrusts were related to the initiation of thin-skinned deformation from Jurassic terrane accretion and were partly contemporaneous with the development of the first clastic wedge (Fernie-Kootenay/Nikanassin/Minnes strata) in the foreland basin. Early Cretaceous dextral oblique slip along the western margin of the Rocky Mountains, with a peak between 136-123 Ma, corresponds to a major Valanginian-Barremian depositional hiatus in the foreland basin followed by the deposition of the Barremian-Aptian Cadomin Formation dominated by conglomerate sheets and multiple diastems of varying duration. In the Front Ranges, the emplacement of the Greenock thrust (103.1 Ma) and Broadview–Snake Indian thrust (99.2 Ma) was contemporaneous with development of Cenomanian deltaic deposits in the immediate foreland. Three thrusts in the Front Ranges, the Rocky Pass (74.8 Ma), Sulfur Mountain (75.6 Ma), and Clearwater (74.2 Ma) thrusts, define a Campanian phase of tectonic loading that led to the last major transgression in the southern portion of the Alberta foreland basin. Along the eastern margin of the Front Ranges, the McConnell thrust (54.0 Ma), together with the Muskeg (52.4 Ma), Brule (53.9 Ma), and Nikanassin (52.1 Ma) thrusts in the Foothills, recorded the last phase of regional contraction. The Late Jurassic, Early Cretaceous, mid-Cretaceous, Late Cretaceous, and early Eocene deformation pulses are separated by relatively long periods of tectonic quiescence. Our data indicate that pulses of tectonic loading in the foreland thrust-and-fold belt trigger flexural subsidence and/or uplift in the foreland basin and are primary controls on the creation or destruction of accommodation space, thus controlling, to a large extent, the type of depositional system and the thickness of depositional sequences.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016