SHIFTING PALEO-ICE STREAMS AND INTER-ICE STREAM ZONES OF THE CANADIAN PRAIRIES

The identification of distinct groupings of streamlined landforms mapped as non-coeval flowsets across large areas of glaciated terrains provide compelling evidence that past ice sheets underwent major glacial dynamics shifts throughout their life cycle. In some regions, like the Canadian prairies, the analysis of remote sensing data and other datasets (e.g. maps and till compositional databases) show that most groupings form internally consistent subglacial sediment-landform assemblages delimited by sharp boundaries. These discrete zones are here referred to as Glacial Terrain Zones (GTZ).

We have developed a model whereby shifting paleo-ice streams play a major role in generating the complex mosaic of prairie GTZ. Corridor-like GTZ consisting mainly of curvilinear mega-scale glacial lineations are interpreted as late-glacial ice stream imprints. Topography and till compositional data together indicate significant overprinting took place through erosion and sediment redistribution underneath these late-glacial paleo-ice streams. Within these corridors multiple topographic steps or prominent sediment ridges (ice stream shear moraines) mark the former position of lateral margins indicating changes in ice stream width. Outside of the late-glacial ice stream GTZ, a complex palimpsest record of ice flow systems is preserved on higher grounds. In our model, these GTZ correspond to the position of late-glacial inter-ice stream zones. Locally, they include older fragmented ice stream corridors and their associated inter-ice stream zones. The high degree of remnant landscape preservation requires rapid propagation of ice streams and their tributaries inside the ice sheet at the expense of pre-existing systems whose landform record becomes partially preserved inside newly-formed inter-ice stream zones where low erosion conditions prevail. The surficial glacial record of the Canadian prairies indicates that terrestrial “prairie” ice streams formed extensive systems which propagated far inside the Laurentide Ice Sheet, experienced major shifts, and likely had a critical influence on the regional deglaciation and rate of ice sheet collapse.