A GIS‐based multi‐proxy analysis of the evolution of subglacial dynamics of the Quebec–Labrador ice dome, northeastern Quebec, Canada

Abstract

The glacial records of the inner-core regions of the Laurentide Ice Sheet (LIS) document complex yet coherent patterns reflecting ice-sheet change (e.g. ice-divide migration), providing unique insights into past glacial conditions. This study develops a conceptual model of subglacial dynamics evolution within a major ice-dispersal centre of the LIS in northeastern Quebec, Canada using a GIS-based analysis of the surficial geologic record. Multiple proxies of subglacial conditions (subglacial streamlined landforms, lake density and lake area over thin drift/bedrock) were analysed through grid-overlay techniques and then classified based on different proxy variables ranging from highly mobile warm-based to immobile cold-based conditions. An additional proxy (till blanket) was used to identify areas of thick till deposition, but with few proxies (few lake or landform metrics). Based on local ice-flow reconstructions, the most 'relict' glacial terrain zone (GTZ1) has warm-based conditions over 66% of its area and is remarkably well preserved, suggesting laterally extensive warm-based conditions during the oldest identified ice-flow phase. This relict glacial terrain is partially overprinted by two subsequent ice-flow phases in spatially restricted zones in the northeast (73% warmbased), east-central (41% warm-based), and northwest (33% warm-based) of the study area. A zone of more sluggish conditions (only 3% warm-based) was identified in the highlands at the centre of the study area, characterized by thin till cover, few landforms, yet with large patches of relatively abundant small lakes, indicative of areal scouring. No clear evidence of sustained cold-based conditions (i.e. high chemical index of alteration values or high 10 Be abundances) was found in the study area. These results suggest that warm-based conditions (active erosion and/or deposition) were uniformly widespread during the earliest ice-flow phase, later becoming more spatially restricted with broader sluggish ice conditions. These spatially restricted regions of warm-based subglacial regimes were likely controlled by surrounding and down-flow ice streaming.

The Ordovician strata of the Ennedi Plateau, northeastern Chad (Erdi Basin)

“…A potential end-Ordovician record have also been inferred in Cameroon, where an undated iceflow pattern toward the WSW has been documented [Caron et al, 2011]. Disparate orientations would not be a real problem because opposite flow orientations might characterize a same glacial event in areas corresponding to former ice divides [Rice et al, 2020].…”

Morphometric analysis of ice scour lakes in Iceland: A proxy for ice sheet dynamics

“…Although many studies investigate lake density and area (e.g., Andrews et al, 1985;Ebert, 2015;Principato & Johnson, 2009;Rea et al, 1998;Rice et al, 2020;Sugden, 1978)…”

“…Packing takes into account lake area and differs from density, which is based on centroids of lakes. Rice et al (2020) points out the importance of calculating both parameters, as they may yield different patterns. To calculate density, a new point shapefile was created in ArcMap 10.8.1 with the feature to point tool, using the natural Icelandic lakes dataset as the input to create a centroid for each lake.…”

“…After glacial retreat, ice scour depressions commonly fill with water and become remnant pockets of intense former glacial erosion. Understanding patterns of glacial erosion provides insight into basal thermal conditions of paleo‐ice sheets and provides important information for glaciological models, and they have been used to understand glacial erosion patterns associated with the British, Fennoscandian and Laurentide Ice Sheets (Andrews et al, 1985; Ebert, 2015; Ebert et al, 2015; Hall et al, 2015; Rea et al, 1998; Rice et al, 2020; Sugden, 1978). Since ice scour lakes are abundant in many formerly glaciated regions, they have the potential to provide valuable information about basal thermal regime and paleo‐ice flow conditions.…”

“…Fennoscandian and Laurentide Ice Sheets (Andrews et al, 1985;Ebert, 2015;Ebert et al, 2015;Hall et al, 2015;Rea et al, 1998;Rice et al, 2020;Sugden, 1978). Since ice scour lakes are abundant in many formerly glaciated regions, they have the potential to provide valuable information about basal thermal regime and paleo-ice flow conditions.…”