ICE-FLOW AND TILL PROVENANCE IN MANITOBA, CANADA; DECODING THE LAURENTIDE ICE SHEET PUZZLE PIECES

Manitoba (Canada) was a dynamic region during the last glaciation, spanning from an inner core region to the periphery of the Laurentide ice Sheet (~900 km north of the LGM max limit). Portions of the Manitoban landscape, especially in the north, are patchy and fragmented palimpsest or relict glacial terrains unrelated to deglaciation. These patches were partially to completely preserved during deglaciation meaning that the ‘youngest’ ice-flow indicators and/or landforms at a site may not have formed during the youngest (last) deglacial events.

We utilize a diverse geologic dataset including glacial geomorphology, field-based ice flow indicators, stratigraphy, till geochemistry, till-clast lithology and detrital hornblende ⁴⁰Ar/³⁹Ar ages to identify these patches and reconstruct the glacial history of the region. Pre-deglacial landscapes can be demarcated by ribbed moraine, small patches of felsenmeer and regolith, fragmented linear and curvilinear streamlined landform flowsets, meltwater features cross-cutting flowsets (corridors and eskers), cross-cutting ice-flow indicators unrelated to the youngest ice-flow phase, and patches of locally-anomalous till composition.

Manitoba was variably glaciated by ice flowing from the Keewatin dome, the Quebec-Labrador dome and the Hudson Bay Ice Saddle. Reconstructed ice-flow phases show that both pre-LGM and a penultimate glaciation followed similar growth patterns, where ice advanced into Manitoba from the east, followed by a switch in ice-flow direction indicating flow from the Keewatin ice centre to the northwest and north. The dominant ice source during MIS 2 deglaciation switched from the Keewatin sector (Souris Lobe and Red River Lobe) to the Hudson Bay Ice Saddle (Pas Lobe, Hayes Lobe, and Stephens Lake sublobe), and then back to the north again (Quinn Lake) with demise of the saddle. As such, hybrid tills produced by multiple cycles of entrainment, reworking, and deposition cover the majority of Manitoba. Deciphering the levels of relative inheritance and overprinting is essential for till stratigraphy studies and effective drift prospecting.