It is generally assumed that regions glaciated by continental ice sheets offer little promise for long paleoenvironmental records due to erosional processes associated with glaciation. We show that beneath portions of the northeastern Laurentide Ice Sheet, characterized by cold-based glaciation, sediment sequences representing multiple interglaciations have been preserved within extant lake basins. Radiocarbon and optically stimulated luminescence dating confirm the antiquity of the sediments, thereby extending the terrestrial paleoenvironmental record of the Canadian Arctic by hundreds of thousands of years. The lake sediment record presented here corroborates numerous recent cosmogenic exposure dating studies indicating complex patterns of erosion beneath polar ice sheets. It also demonstrates that the presence of intact interglacial sediments does not demand unglaciated refugia. Similarly ancient sediments may be preserved in many regions formerly covered by Pleistocene ice sheets.