The Late Jurassic to Early Cretaceous fill of the Western Interior foreland basin is characterized using geochronological data in order to assess the stratigraphic expression of wedge-top geomorphology, as controlled by sediment cover and denudation. In northern Montana, USA, and Alberta, Canada, wedge-top deposits are poorly preserved; however, their former presence may be inferred from the detrital record in the foreland basin. We present new U/Pb detrital zircon data from nine samples collected near Great Falls, Montana, augmented with field data. The stratigraphy at Great Falls is characterized by Late Jurassic marine and nonmarine deposits, which are truncated by a basinwide sub-Cretaceous unconformity. Aptian and lower Albian strata overlying the unconformity are dominated by nonmarine deposits, which transition up-section into a predominantly marine succession related to a major transgression of the Boreal Seaway in the Albian.Detrital zircon grains from Great Falls strata yield age spectra that can be subdivided into three groups using multidimensional scaling. Group 1 is characterized by diverse zircon populations, which are interpreted to record recycling of pre-Cordilleran sedimentary strata transported via foreland basin-axial river systems with headwaters in the southwestern United States. Group 2 is characterized by the dominance of Mesozoic detrital zircon grains, which are interpreted to record sediment dispersal by fluvial systems with headwaters in the Cordillera. Group 3 is intermediate between groups 1 and 2, based on its proportion of Mesozoic zircon grains. This group records a diversification of the provenance from one dominated by Cordilleran igneous rocks to include recycled sedimentary strata.New data are integrated with three other data sets from Montana and Alberta such that stratal thicknesses (a proxy for accommodation development) and provenance evolution can be compared across the basin. The detrital record in each area, which transitions from diverse provenance to predominantly Cordilleran through the entire stratigraphic section, can be linked to the burial of the pre-foreland strata in the wedge-top depozone. This record elucidates a period of evolution of the western margin of North America to a more Andean-type system with primary input to the basin from an active magmatic arc.

Jurassic-Cretaceous sedimentary rocks of the Alberta foreland basin are a key record of the evolution of the Canadian Cordillera. We test a recent model for cyclical development of Cordilleran orogenic systems using detrital zircon analysis of the major sandstone units deposited between 145 and 80 Ma exposed in the Rocky Mountain Foothills near Grande Cache, Alberta. The basin history is well constrained by decades of study, and the stratigraphy has been previously subdivided into tectonostratigraphic wedges. U-Pb data from 14 detrital zircon samples are included in this study. All the major magmatic provinces of North America are represented in each sample, with the relative proportions varying between samples. The samples are assigned to five groups with the aid of multidimensional scaling. Groups 1-3 are interpreted to record recycling from specific passive-margin units of western North America with varying input from the Cordilleran magmatic arc. Group 4 is interpreted to record recycling from sedimentary strata in the United States and dispersal by basin-axial fluvial systems. Group 5 is dominated by Mesozoic zircon grains interpreted to have originated in the Cordilleran magmatic arc. Detrital zircon age spectra do not form groups based on the tectonostratigraphic wedges from which they were sampled; rather, within each tectonostratigraphic wedge, they exhibit evolution from diverse age spectra to a less-diverse distribution of detrital zircon ages. We constructed a proxy for magmatic flux of the Cordilleran magmatic arc using detrital zircon ages younger than 200 Ma; it shows three modes at ca. 165, 115, and 74 Ma. These ages are considered high-flux episodes of magmatism that are linked to cyclical uplift and plateau formation in the orogen. This cyclical process is interpreted to: (1) control sedimentation rates in the foreland; (2) account for evolving provenance by altering catchments; and (3) be a plausible mechanism for the deposition of the tectonostratigraphic wedges in the Alberta foreland basin.

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