Abstract

Oriented blocks of till from 31 sites were obtained from the Late Wisconsin St. Joseph Till over a distance of about 208 km along the east coast of Lake Huron. An analysis of paleomagnetic remanence data shows that two units within the St. Joseph Till were sampled, although it has not been possible to find a consistent stratigraphic break from field examinations. These two units give separate virtual geomagnetic pole (VGP) positions of lat. 67.1 °N, long. 297.8 °W and lat. 65.1 °N, long. 220.6 °W. Remanence data from varved clays for the Walkerton area, which were deposited at about the same time as the St. Joseph Till, gave a VGP position close to the mean of all remanence results from the St. Joseph Till. A spruce log extracted from the till was dated at 13 100 ± 110 y B.P. (GSC-2213), which is consistent with the time of the Port Huron ice advance.Granulometric analysis, carbonate analysis, and pebble analysis showed variations which are directly related to the nature of the underlying bedrock and could not be used to differentiate the two till units. Ratios of purple (dark red) to white (light red) garnets also demonstrate the presence of two till units within the St. Joseph Till and thus support the interpretation of the remanence data.The results show that in the absence of direct field evidence remanence data is a sensitive tool which can be used to determine if more than one till unit is present.

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