Compositional Variations In The St Joseph Till Units In The Goderich Area

Compositional variation in the St. Joseph Till was examined at five sections over a 55 km distance, along the eastern shore of Lake Huron. A collection of stratified samples at these locations indicates that the St. Joseph Till can be separated into lower and upper till units by the occurrence of a semi-continuous layer of waterlain sediment throughout the study area. The separation indicates that a previously unrecognized glacial retreat occurred in the Lake Huron area.;Local spatial variation was examined in detail at the Pt. Albert section. Granulometric, carbonate, major and trace element analyses of samples collected from three vertical sampling lines demonstrate that the lower and upper units can be locally differentiated by matrix composition, although both units are similar in the field. Variation enables recognition of four main sources incorporated during glaciation.;The lower unit displays an overall gradation in matrix composition and a progressive increase in distal clasts upward. The overall gradation can be further subdivided into distinctive layers of homogeneity and layers of transition that show compositional values gradational between homogeneous zones. The layers alternate vertically and a statistical treament employing Q-mode clustering and multivariate discriminant analysis confirms the layering in both lower and upper units.;Matrix composition in the main part of the upper unit is characteristically homogeneous and enables comparisons of major element content of the till and estimates of local and regional composition. The comparisons imply that the chemical composition of the till is biased in favour of the nearby Paleozoic source rocks.;The regional variation in matrix composition was found to vary with distance. This inhibits differentiation of the units on a regional scale, although they can be separated in sections by vertical changes in composition and stratigraphic position. The incorporation of local bedrock is recognized by changes in matrix and clast content on both local and regional scales. These changes indicate that Paleozoic bedrock was incorporated, comminuted and dispersed as clasts and matrix particles within a distance of about 13 km.;A paleomagnetic signature was recovered from the till units and will be useful for future correlations