Subglacial and ice‐marginal landforms in south‐central Ontario: implications for ice‐sheet reconfiguration during deglaciation

Abstract

Regional‐scale, high‐resolution terrain data permit the study of landforms across south‐central Ontario, where the bed of the former Laurentide Ice Sheet is well exposed and passes downflow from irregular topography on Precambrian Shield highlands to flat‐lying Palaeozoic carbonate bedrock, and thick (50 to >200 m) unconsolidated sediment substrates. Rock drumlins and megagrooves are eroded into bedrock and mega‐scale glacial lineations (MSGL) occur on patchy streamlined till residuals in the Algonquin Highlands. Downflow, MSGL pass into juxtaposed rock and drift drumlins on Palaeozoic bedrock and predominantly till‐cored drumlins in areas of thick drift. The Lake Simcoe Moraines, now traceable for more than 80 km across the Peterborough drumlin field (PDF), form a distinct morphological boundary: downflow of the moraine system, drumlins are larger, broader and show no indication of subsequent reworking by the ice, whereas upflow of the moraines, a higher degree of complexity in bedform pattern and morphology is distinguished. Discrete radial and/or cross‐cutting flowset terminate at subtle till‐cored moraine ridges downflow of local topographic lows, indicating multiple phases of late‐stage ice flow with strong local topographic steering. More regional‐scale flow switching is evident as NW‐orientated bedforms modify drumlins south of the Oak Ridges Moraine, and radial flowset emanate from areas within the St. Lawrence and Ottawa River valleys. Most of the drumlins in the PDF formed during an early, regional drumlinization phase of NE–SW flow that followed the deposition of a thick regional till sheet. These were subsequently modified by local‐scale, topographically controlled flows that terminate at till‐cored moraines, providing evidence that the superimposed bedforms record dynamic ice (re)advances throughout the deglaciation of south‐central Ontario. The patterns and relationships of glacial landform distribution and characteristics in south‐central Ontario hold significance for many modern and palaeo‐ice sheets, where similar downflow changes in bed topography and substrate lithology are observed.

An erosional origin for drumlins of NW Poland

“…The pattern of SSBs in the Stargard drumlin field compared with the morphology of the land surface preceding the last ice advance reconstructed by Hermanowski (2015) (Figure 6A, B) suggests that the ice flow was to some extent topographically controlled. This pattern is consistent with findings elsewhere (Evans et al, 2008;Kessler et al, 2008;Ross et al, 2009;Winsborrow et al, 2010;Rignot et al, 2011;Margold et al, 2015;Fransner et al, 2017;Mulligan et al, 2019), although areas where bed topography exerted little influence on the ice flow are also known (Ross et al, 2009;Stokes et al, 2013b). The relief difference in the area overridden by the drumlinizing ice stream was up to~70 m ( Figure 6B), which is significant given the location of this terrain at the ice-sheet periphery where the ice was thin.…”

Diversity of murtoos and murtoo‐related subglacial landforms in the Finnish area of the Fennoscandian Ice Sheet

“…Recent studies have demonstrated significant spatial and morphological variability of subglacial landforms, for example, due to changing basal thermal regimes and the dynamic behaviour of ice sheets (e.g. Mulligan et al 2019;Evans et al 2020). In examining the geomorphic characteristics of murtoos, it is important to recognize that a distinction between murtoo-type 'end members' (Fig.…”

Glacial geomorphology of the Neutral Hills Uplands, southeast Alberta, Canada: The process-form imprints of dynamic ice streams and surging ice lobes

“…This palaeoglaciological signature has been likened to the terrestrial equivalent of ice stream/troughmouth fan systems of submarine settings (Evans et al, 2012), and on the prairies is representative of marginal lobation and partial overprinting along the termini of fast ice flow corridors (Patterson, 1997(Patterson, , 1998Colgan et al, 2003;Jennings, 2006;Evans et al, 2008;Ó Cofaigh et al, 2010;Margold et al, 2015;Norris et al, 2018). The role of surging and changing basal thermal regimes in driving spatial and temporal variability in landsystems associated with lobate ice stream margins are being increasingly emphasised as higher resolution geomorphological mapping is undertaken (e.g., Mooers, 1990;Colgan et al, 2003;Evans et al, 2014Evans et al, , 2016aSookhan et al 2018;Mulligan et al 2019). Additionally, thinning and recession of these ice margins occurred down the adverse slope of the regional drainage gradient, which promoted the development of large proglacial lakes, gave rise to complex meltwater drainage patterns and ice-contact glacifluvial features (Christiansen, 1979;Kehew and Lord, 1986;Evans, 2000;Clayton et al, 2008;.…”