Till variability and compositional stratification: examples from the Port Huron lobe

Abstract

Compositional variability provides important clues to the glacigenic mechanisms of entrainment and transportation of debris and deposition of basal tills. This paper examines contrasting homogenization and stratification of textural and geochemical composition for two late Wisconsinan till units, exposed in a near-vertical section at Port Albert, Ontario. Q-mode cluster and multivariate discriminant analysis are used to delineate compositional layers, which occur in both units, although in the upper unit the distinction is less noticeable because of compositional homogeneity. It is inferred that compositional stratification is inherent in the entrainment process, whereas englacial thrusting and shearing tend to homogenize the glacial load. It is suggested that recognition of the degree of homogenization or the occurrence of stratification is essential for the application of analytical results in the study of till units.