Regional stagnation of the western Keewatin ice sheet and the significance of meltwater corridors and eskers, northern Canada

D.R Sharpe,B.A Kjarsgaard,J.-E Lesemann,R.D Knight

doi:10.1139/cjes-2020-0136

D.R Sharpe, B.A Kjarsgaard + Show 2 more

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https://doi.org/10.1139/cjes-2020-0136

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Abstract

The glacial land system of western Keewatin region, northern Canada, consists of three significant events: (1) regional emplacement of subglacial sediments, mainly till; (2) landscape erosion with development of an integrated, anabranched network of meltwater drainage routes leading to meltwater corridors; and (3) deposition of an extensive array of eskers, and related landforms, within meltwater corridors. Integration of extensive field observations, mapping, and remotely sensed data allow us to link scoured bedrock and till surfaces, truncated drumlins, scour pits, glaciofluvial terraces, boulder lags, and a large-scale network of corridors, as part of regional meltwater erosion events. The network of long (∼100–200 km), relatively wide (∼1–3 km) meltwater corridors record confined subglacial erosion that scoured sediment (and bedrock) prior to glaciofluvial sedimentation (predominately eskers). Despite considerable sediment erosion along meltwater corridors, moraines and other ice-marginal deposits are rarely observed on the western Keewatin landscape. The absence of these features is inconsistent with deglacial models relying on step-wise active retreat of the ice margin. Instead, we propose that deglaciation of the western Keewatin sector of the Laurentide Ice Sheet was predominantly controlled by regional thinning and stagnation. These findings raise fundamental questions about deglacial patterns and processes and thus suggest that further evaluation and revision of existing models of deglacial chronology for this sector of the Laurentide Ice Sheet is needed.

Highlights

The Keewatin sector of the former Laurentide Ice Sheet (LIS) has played a prominent role in our understanding of glacial advance and retreat patterns of the ice sheet (e.g., Prest 1969; Dyke and Prest 1987a)
We propose that regional stagnation was more prominent during deglaciation (e.g., Shilts et al 1979; Shilts 1985) of the western Keewatin region rather than step-wise ice-marginal retreat
In western Keewatin, moraines and other ice-marginal landforms are sparse and most eskerridge fans (Figs. 4, 7) or scattered till ridges cannot be linked to purported ice margins

Summary

Introduction

The Keewatin sector of the former Laurentide Ice Sheet (LIS) has played a prominent role in our understanding of glacial advance and retreat patterns of the ice sheet (e.g., Prest 1969; Dyke and Prest 1987a). Intercorridor areas are defined by till-blanket, drumlins, interfluves between corridors where evidence of meltwater erosion occurs, and erosional residuals, as defined by truncated drumlinized uplands, terraced, drumlinized surfaces (Fig. 2), corridor margins, scoured surfaces with clast armours, and lags These intercorridor observations indicate that flows were initially broad before collapsing to multiple channels, entrenching to corridors. Observations reported from extensive drumlin fields across the Keewatin region (Shaw et al 2010) and in the study area (Fig. 4) have little overlying sediment/landforms, except for disorganized, isolated esker ridges (Fig. 5; Kerr et al 2013a). In western Keewatin, moraines and other ice-marginal landforms are sparse and most eskerridge fans (Figs. 4, 7) or scattered till ridges cannot be linked to purported ice margins

Findings

Discussion

Summary and conclusion