UNDERSTANDING THE ORIGIN OF GLACIAL LANDSCAPES USING GIS IMAGING OF DEPOSITS FORMED ALONG THE SOUTHERN MARGIN OF THE LAURENTIDE ICE SHEET

Ice sheet models that reconstruct past glacier behaviour have assisted in understanding the large scale distribution of glacial landscape types. However, these models have limited success when applied to the interpretation of smaller, more regional patterns of glacial deposition, especially in areas influenced by complex interactions of depositional processes such as those that existed along former ice sheet margins. These areas are characterized by complex distributions of sediments and landforms and in many cases, geological data are not readily available on appropriate scales to validate modeling results.

Southern Ontario was covered by the lobate margin of the late Wisconsin Laurentide Ice Sheet (LIS) and extensive subglacial till sheets were deposited across the region. As the ice sheet withdrew, lakes formed around its margin and extensive outwash deposits were deposited. Minor readvances of the ice margin during retreat created numerous small push moraines. This region holds a detailed record of the behaviour of the LIS during retreat but geologic data are not available at a scale or form appropriate for modeling purposes.

Recent publication of digital format data regarding surface topography and subsurface sediment distribution, together with geological survey maps of surface sediment types, has allowed compilation of a series of GIS images of glacial deposits and landforms across southern Ontario. GIS images of bedrock type, bedrock topography, Quaternary sediment thickness and surficial landforms show how bedrock variables have affected glacial landscape evolution. Visualization of the relationship between surface sediment types and landforms is made possible by draping maps of these features onto 3D elevation models. Images showing the distribution of different types of moraines across the region may be used, in conjunction with field data regarding sediment composition, to infer the relationship between moraine type and ice marginal conditions.

GIS imaging of glacial deposits and landforms provides a new investigative tool to employ in the reconstruction of glacial depositional histories and ice margin behaviour across southern Ontario. These images may also be used to help reconstruct paleoglaciological conditions and validate glacier flow models.