Drumlinized tunnel valleys in south-central Ontario

Mulligan, R P M; Bajc, Andy F.; Eyles, Carolyn H.

doi:10.1016/j.quascirev.2018.07.026

Cited by 12 publications

(34 citation statements)

References 97 publications

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“…) that pre‐date regional drumlinization of NT (Mulligan ; Mulligan et al . ). The valleys within the study area, despite being smaller in scale, bear many morphological similarities to those observed to the west: they are commonly flanked by NT along their lateral margins and contain drumlins along their flanks and within central parts of valley axes.…”

Section: Discussionmentioning

confidence: 97%

“…; Mulligan et al . ). The valleys record the development of channelized subglacial drainage systems that began prior to regional bedform development and persisted throughout deglaciation, as indicated by the preferential occurrence of eskers within and along the flanks of valleys (Brennand ; Brennand & Shaw ; Figs ), the incision of till within parts of some valleys, and partial infill of valleys with coarse‐grained sediments, particularly in close proximity to the ORM (Sharpe et al .…”

Section: Discussionmentioning

confidence: 97%

“…This, and later models (Ministry of Natural Resources andForestry 2010, 2014a, b), greatly improved visualization of terrain elements and glacial landforms across southern Ontario, permitting more detailed, statistical analyses of drumlin morphology, orientations, distribution, and clustering within the PDF (Maclachlan & Eyles 2013). Surficial mapping integrated with terrain analysis has identified new complex sediment-landform assemblages and erosional features within different parts of the PDF, recording different intensities of bedform genesis and postglacial erosion throughout the region (Marich 2014(Marich , 2016Eyles & Doughty 2016;Mulligan et al 2016Mulligan et al , 2018aSookhan et al 2018a). Recently released high-resolution terrain models and aerial photographs (Ministry of Natural Resources and Forestry 2010, 2014a, b) provide the detailed morphological information required to shed new light on previous work within the PDF and surrounding areas, and to place observations of bedform relationships and composition into a broader regional context at the scale of former ice lobes/streams.…”

Section: Historical Studiesmentioning

confidence: 99%

“…Convergent and divergent patterns of bedform long axes strongly coincide with topographic lows, including gaps in bedrock escarpments and valleys cut into Pleistocene sediments (Figs 4,5) that were previously interpreted as lateglacial tunnel channels (Brennand & Shaw 1994;Sharpe et al 2004). However, sediment-hosted valleys in the western part of the valley network have recently been interpreted as tunnel valleys (sensu stricto; Clayton et al 1999) that pre-date regional drumlinization of NT (Mulligan 2013;Mulligan et al 2018a). The valleys within the study area, despite being smaller in scale, bear many morphological similarities to those observed to the west: they are commonly flanked by NT along their lateral margins and contain drumlins along their flanks andwithin central parts of valley axes.…”

Section: Landform Relationshipsmentioning

confidence: 99%

“…Surficial mapping integrated with terrain analysis has identified new complex sediment‐landform assemblages and erosional features within different parts of the PDF, recording different intensities of bedform genesis and postglacial erosion throughout the region (Marich , ; Eyles & Doughty ; Mulligan et al . , ; Sookhan et al . ).…”

Section: Introductionmentioning

confidence: 99%

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

Mulligan

Eyles

Marich

2019

Boreas

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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.

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Section: Discussionmentioning

confidence: 97%