DETRITAL ZIRCON GEOCHRONOLOGY OF UPPER CRETACEOUS AND PALEOGENE STRATA, ALBERTA BASIN, CANADA: IMPLICATIONS FOR PROVENANCE AND TECTONIC EVOLUTION

The linkage between tectonics and sediment deposition in the Alberta foreland basin is loosely constrained. In this study we consider the relationship between the timing of: (1) Cordilleran magmatism; (2) foreland basin subsidence; (3) denudation of the mountain belt; and (4) thrusting in the Rocky Mountain fold and thrust belt through analysis of the Upper Cretaceous–Paleogene stratigraphic wedge in the basin. Detrital zircon geochronology reveals that magmatism was ongoing throughout this phase of basin evolution, and provides evidence for uplift and denudation of the mountain belt. Geochronology results are compared to mapped thickness trends of units in the basin (e.g., Belly River Group, Horseshoe Canyon Formation), which provide a proxy for accommodation development. These geochronology and stratigraphy data are considered with respect to recently obtained thrust-faults ages.

Regional isopach mapping reveals asymmetric sedimentary foreland basin deposits, initiated at the onset of Belly River Group deposition at 78.85 ±1.95Ma. From this time until ~66.8 Ma, thick successions of siliciclastics are preserved in the foreland basin, recording denudation of the uplifted orogenic belt. Detrital zircon geochronology of Cretaceous deposits provide a proxy for the volume of magmatism in the Omineca belt (N = 15 samples; n = 3176 ages, total), indicating a magmatic peak at 73.5 Ma. Peak magmatism was coincident with thrusting (72.3-75.6 Ma) based on recently acquired radiometric fault gauge ages. We interpret this to record a major phase of orogenesis in the hinterland. Peak magmatism and faulting post-dates initial basin subsidence by 4-6 Ma. Collectively, these data provide crucial age-constraints to processes commonly calculated with numerical models or speculated upon by theoretical models.