POST-OROGENIC GRAVEL TRANSPORT AND THE DETRITAL ZIRCON PROVENANCE OF CENOZOIC FLUVIAL CONGLOMERATES ON THE CANADIAN PLAINS

Cenozoic fluvial conglomerates and sandstones exposed across the plains of western Canada record an episode of post-orogenic gravel transport following the Cordilleran and Laramide orogenies. We collected over 15 samples for detrital zircon U-Pb geochronology in an effort to better understand the sediment provenance of these deposits and gain insight into the Cenozoic evolution of the Canadian Cordillera and adjacent Plains. The Swan Hills and Hand Hills conglomerates in central Alberta contain similar detrital zircon populations of 60-200, 1700-1900, and 2600-3000 Ma. Conglomerates at Del Bonita and Cougar Ridge in southwestern Alberta contain populations of ca. 70 and 185 Ma and minor populations of 470, 770 and 1800 Ma. Eocene-Miocene conglomerates exposed in southern Alberta and Saskatchewan contain detrital zircon populations with ages of 30-120, 1700-1800, and 2400-3200 Ma. The Pliocene Souris River Gravels in southern Manitoba contain detrital zircons with age populations of 30-200, 400, 1200, 1700, and 2600-3000 Ma. All of the conglomerates are interpreted as having been derived from Cordilleran arc sources and material recycled from rocks exposed in the northern US Rockies and southern Canadian Cordillera. Multidimensional scaling comparisons suggest the samples can be divided into several groups, most notably the conglomerates in central Alberta and those exposed along the southern Canadian Plains. The ancient rivers associated with these conglomerates are believed to have been part of the Bell River system: a transcontinental fluvial system that crossed northern North America and emptied into the Labrador Sea. Progradation of the gravels, exhumation of underlying foreland basin strata, and eastward-shifting depocenters suggests broad-wavelength, post-orogenic rock uplift occurred in the foreland area of the Canadian Rockies.