DETRITAL ZIRCON DATA FROM PALEOGENE-NEOGENE FLUVIAL CONGLOMERATES ON THE CANADIAN PLAINS

Outcrops of Cenozoic fluvial conglomerates and sandstones are exposed across the plains of western Canada and the northern US. These units are located hundreds of kilometers from the nearest topography and were deposited millions of years after upper-crustal shortening in the Canadian and US Rockies had ceased. We sampled the Ravenscrag Formation, Cypress Hills Formation, Wood Mountain Formation, Hand Hills Conglomerate, and Souris River Gravels for detrital zircon geochronology in an effort to better understand the Cenozoic evolution of the Rockies and the western plains. The Ravenscrag Formation, which underlies the Cenozoic conglomerates in several locations, contains late Mesozoic (70-130 Ma), Paleoproterozoic (~1700 Ma), and minor Archean (~2400 Ma) detrital zircons. The Eocene-Miocene Cypress Hills Formation in Alberta and Saskatchewan contains late Mesozoic (65-120 Ma), Paleoproterozoic (1700-1800 Ma), and Archean (2600-3000 Ma) detrital zircons. The Miocene Wood Mountain Formation in southern Saskatchewan contains late Mesozoic – Cenozoic (20-110 Ma), Paleoproterozoic (~1700 Ma), and minor Archean (2400-3200 Ma) detrital zircons. The Pliocene Souris River Gravels contain detrital zircons with Mesozoic-Cenozoic (30-200 Ma), Paleozoic (400 Ma), Mesoproterozoic (~1200 Ma), Paleoproterozoic (~1700 Ma), and Archean (2600-3000 Ma) ages. The Hand Hills Conglomerate contains detrital zircons with Mesozoic-Cenozoic (60-200 Ma), Paleoproterozoic (1700-1900 Ma), and Archean (2600-3000 Ma) ages. The Ravenscrag Formation and the overlying Cypress Hills Formation contain different detrital zircon populations, suggesting a change in provenance occurred as the Cordilleran system transitioned from contractional to extensional deformation. Provenance of the Wood Mountain Formation is consistent with the underlying Cypress Hills Formation, with the addition of a large proportion of zircons with ages less than 50 Ma. Detrital zircon populations in Cypress Hills and Wood Mountain formations are similar to those of the Renova Formation in southwest Montana, suggesting a similar provenance.