Forty-two Cretaceous and Paleocene sand samples from offshore Labrador and onshore western Greenland were examined petrographically. The sands were found to be mineralogically and texturally immature, reflecting rapid erosion and transportation from local, high-relief source areas. The principal source-rock types were acidic plutonics and amphibolite-facies metasediments and metavolcanics. Basic igneous rocks provided minor quantities of detritus, whereas contributions from sedimentary and low-grade-metamorphic sources were negligible. Cretaceous and Paleocene sediment transport was essentially perpendicular to the axis of the 'Labrador–Baffin rift system.In view of the apparent local abundance of amphibolite-facies supracrustal rocks during the Cretaceous and Paleocene, extensive post-Paleocene denudation in Labrador, Baffin Island, and western Greenland is invoked to account for the present scarcity of such rock types.