Neoproterozoic fluvial quartzarenites from the Shaler Group on Victoria Island in the western Canadian Arctic yield a diverse suite of detrital zircons. U-Pb ages from single zircons fall into three modes: Archean (3.01-2.62 Ga), Paleoproterozoic (1.97-1.84 Ga), and Meso proterozoic (1.64-1.03 Ga). Particularly intriguing is the unusually high proportion (50%) of the Mesoproterozoic mode, as the nearest exposed source is the Grenville structural province, ∼3000 km southeast of Victoria Island. Unimodal northwest paleocurrents, obtained from cross-bedding, are compatible with a southeasterly provenance. These data, supported by sedimentological evidence from the Shaler Group and from correlative strata in the northwestern Canadian Cordillera, imply the existence of a large, perennial river system flowing north-westward from the Grenville orogen. An analogy with the Llanos drainage basin in Venezuela and Colombia is proposed on the basis of similar geography, climate, and sedimentation. These data also provide a maximum age for the Shaler Group (basal Reynolds Point Formation) of about 1.11 Ga.