End moraine construction by incremental till deposition below the Laurentide Ice Sheet: Southern Ontario, Canada

Abstract

Eyles, N., Eyles, C., Menzies, J. & Boyce, J. 2010: End moraine construction by incremental till deposition below the Laurentide Ice Sheet: Southern Ontario, Canada. Boreas, 10.1111/j.1502‐3885.2010.00171.x. ISSN 0300‐9483. Just after 13 300 14C a BP in central Canada, the retreating Ontario lobe of the Laurentide Ice Sheet briefly re‐advanced westwards through the Lake Ontario basin to build a large end moraine. The Trafalgar Moraine (27 km long, 4 km wide) is composed of a distinctly red‐coloured silt‐rich till (Wildfield Till, up to 16.5 m thick) formed by the reworking of proglacial lake deposits and soft shale bedrock. The moraine has a pronounced ramp‐like longitudinal form passing upglacier into fluted till resting on exposed shale. Analysis of water well stratigraphic data, drilled sediment cores, downhole gamma‐ray logs and exposures in deep test pits shows that within the moraine the Wildfield Till is built of superposed beds up to 7 m in thickness. These are inferred to result from the repeated incremental deposition of fine‐grained debris being moved towards the ice margin as a deforming bed such as identified at modern glaciers. A total till volume of 0.81 km3 was produced in a very brief time‐span along a transport path probably no greater than 10 km in length. Subglacial mixing of pre‐existing sediment and soft shale was clearly a very effective process for generating and moving large volumes of till to the ice margin. Similar till‐dominated end moraines occur widely around the margins of the Great Lake basins, where the markedly lobate margin of the retreating Laurentide Ice Sheet re‐advanced repeatedly into proglacial lakes and over fine‐grained sediment. This suggests the wider applicability of the till transport and incremental depositional model presented here.

Insights into subglacial processes inferred from the micromorphological analyses of complex diamicton stratigraphy near Illmensee-Lichtenegg, Höchsten, Germany

“…Likewise, rotation structures are confined within individual subfacies units. At the same time an erosional contact was made with many subjacent sediment units (Iverson et al 1998;van der Meer et al 2003;Piotrowski et al 2004;Eyles et al 2010). Deformation is largely non-pervasive in style and is apparently temporally confined to small areas of the till, but it occurs ubiquitously over time and depth throughout the subglacial sediment pile (cf.…”

Subglacial deforming bed conditions recorded by late Quaternary sediments exposed in Vineland Quarry, Ontario, Canada

“…The Quaternary sediments exposed at the Vineland Quarry show a remarkably consistent change in the intensity of sediment deformation up-section, and fully align with theoretical models describing subglacial deformation processes. This suggests that the deformation signature is the result of a single event that may have been relatively short-lived and could record rapid movement of ice across the area in a similar fashion to that proposed for ice marginal surges (Costello and Walker, 1972;Boyce and Eyles, 1991;Eyles et al, 2011). This interpretation, of rapid ice movement is consistent with the recent interpretations of other late glacial moraines fringing the Ontario basin and suggests that the Port Huron ice margin flowed rapidly out of the western Ontario basin, possibly as an ice surge, supported by a bed of soft, wet sediment (Clarke, 1987;Evans et al, 2006;Eyles et al, 2011).…”

“…This suggests that the deformation signature is the result of a single event that may have been relatively short-lived and could record rapid movement of ice across the area in a similar fashion to that proposed for ice marginal surges (Costello and Walker, 1972;Boyce and Eyles, 1991;Eyles et al, 2011). This interpretation, of rapid ice movement is consistent with the recent interpretations of other late glacial moraines fringing the Ontario basin and suggests that the Port Huron ice margin flowed rapidly out of the western Ontario basin, possibly as an ice surge, supported by a bed of soft, wet sediment (Clarke, 1987;Evans et al, 2006;Eyles et al, 2011). Rapid ice movement and deforming bed conditions may have been promoted by the development of extensive proglacial lake bodies between the advancing ice margin and the topographic barrier of the Niagara Escarpment that allowed both the accumulation of easily deformed clay-rich sediments and the partial buoyancy of the ice margin.…”

“…Similar ice marginal environments are known to have existed elsewhere in the Great Lakes basins during the Quaternary and examples of subglacially deformed proglacial lacustrine sediments can be found farther afield in areas such as Scotland (Banham, 1977;Golledge, 2007), northern Venezuela (Mahaney et al, 2004), southwest Ireland (Cofaigh et al, 2010) and the state of Illinois in the United States (Johnson and Hansel 1990). A modern analog for this type of glacial setting can be identified in Antarctica where Ice Stream B flows rapidly over clay-rich subglacial debris (Alley et al, 1997;Eyles et al, 2011).…”

High-resolution LiDAR mapping of glacial landforms and ice stream lobes in Finland

“…2), reflecting the delivery of much subglacial debris to the margin by advection of 'soft' deforming till (e.g. Eyles et al, 2011). Such debris is partially reworked subglacially by canalized meltwater streams and left as esker-fan complexes or much larger sandur plains during ice retreat (Fig.…”