THE SUBGLACIAL MOSAIC: EXAMINING THE GEOLOGIC RECORD OF SUBGLACIAL LANDSCAPE EVOLUTION (Invited Presentation)

The erosional and depositional landforms found within previously glaciated landscapes result from the net effect of subglacial processes at work over the lifetime of an ice sheet. In turn, landforms and subglacial topography modify the ice flowing over them through relationships with basal shear stress and bed topography. Thus, the deposition or erosion of sediment from an ice sheet’s bed is intrinsically connected to basal boundary conditions, such as roughness or shear strength, information useful in constraining paleo-ice-sheet reconstructions. Through the examination of glacial landscapes from core regions of the Laurentide Ice Sheet at the macro- (tens of kilometers) and meso- (kilometer) scale, we identify a high-degree of spatial and temporal variability in the dominant sub-glacial processes recorded in the geologic record. In northern Manitoba, thick glacial sediment sequences generated by multiple glaciations occur in conjunction with perpendicular surficial streamlined landforms. The interpretation of these landscapes provides evidence for both ice divide migration and variable basal thermal regimes, likely in response to the waxing and waning influence of the Keewatin and Quebec-Labrador dispersal centers. In contrast, in the central Northwest Territories, a dominantly erosive regime has stripped away much of the glacial sediment, leaving only patchy discontinuous till cover. Despite the limited depositional record, local till composition bears evidence of multiple dispersal vectors, likely tied to the shifting Keewatin divide, indicating the usefulness of the geologic record, even within dominantly erosive regimes. Despite the creation of detailed relative ice flow histories, significant questions remain regarding the timing and duration of ice flow phases, spatial continuity of basal thermal regimes, as well as their connections to past climate. In total, a wealth of paleo-glaciological information is available in the geologic record of past ice sheets, which provides the potential for investigations into the net effect of subglacial processes on sediment generation and transport, the attendant effect on ice flow, as well as possible connections to changes in paleoclimate.