Reconstruction of Wisconsinan-age ice dynamics and compositions of southern Ontario glacial diamictons, glaciofluvial/lacustrine, and deltaic sediment

Abstract

Macrofabric analysis of till sections in south-central Ontario confirms that clast orientation yields information related to changing ice dynamics during the Wisconsinan glaciation. Test stations in six sections yield unimodal to multimodal macrofabrics that indicate ice flow direction, ranging from SE–NW vectors when ice was thin and flowing radially to variable NE–SW, NNE–SSW, and N–S vectors when ice thickened. Ice loci appear to range from the Lake Ontario basin and southern Quebec (thin ice), Labrador Ungava (thicker ice), and Hudson Bay (thickest ice). The north–south fabric may identify the intergrowth of Keewatin–Labrador ice, presumably the maximum ice thickness of the Last Glacial Maximum (LGM). The preliminary data support the theory that topography directed ice movement during preliminary and closing stages of glaciation in southern Ontario, while thick ice generated flow vectors largely unaffected by underlying topography; hence, leading to clast azimuthal variations reflecting changing ice loci with glacier growth. The fabrics analyzed suggest that inferring difference between ductile and brittle lodgement tills is possible as well as to identifying possible glacial tectonic action/overburden loading that disturbs the least friction-fit position of clasts in till. The changing dynamics within till sheets are supported, in part, by variations in glacial crushing seen in SEM imagery that depict a range of microtextures from full-scale fractures under brittle conditions to those indicating less viscous transport under ductile regimes. To some degree, changes in flow direction are further supported by geochemical variations that relate to bedrock/regolith up-glacier controlling Ca-dilution and variable concentrations of Rare Earth Elements (REEs).