Abstract

Field observations and theoretical studies on temperate glaciers suggest that there is a layer of water at the ice–sediment interface. If this condition existed under continental glaciers it is reasonable to assume that rock and mineral particles were released from the base of the ice through a water or slurry medium.In order to test this hypothesis, samples of clay till from Port Alma, Ontario, were tested and shown to have a strong component of detrital remanent magnetization (DRM) which resists alternating field demagnetization. The possibility that the remanence alignment was caused by glacier movement has been ruled out by anisotropy of magnetic susceptibility measurements. Thus the results demonstrate that a water or slurry layer existed at the base of continental glaciers at the time of till deposition. The basal water layer may explain the very rapid advance of the glacier lobes through the basins of the Great Lakes. The paleomagnetic data and available radiocarbon dates suggest that the till at Port Alma was deposited in a relatively short period of about 100 to 400 yr. The potential usefulness of DRM in clay-rich tills for stratigraphic studies is being further investigated.

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