Comment on “Converging ice streams: a new paradigm for reconstructions of the Laurentide Ice Sheet in southern Ontario and deposition of the Oak Ridges Moraine”

Russell, H A J

doi:10.1139/cjes-2018-0191

Cited by 3 publications

(2 citation statements)

References 29 publications

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“…The mapped sediment record in the ORM area (Fig. 3), however, is not compatible with these ice‐streaming models (Russell 2019; Sharpe & Russell 2020; Table S2). In brief, the ice stream transport model is contradicted by: (i) sparse ice stream sediment (Halton Till) along the flow path; (ii) no ice‐stream (Halton) streamlined landforms; (iii) scant ice‐stream sediment (Halton Till) at the ORM ice margin (Fig.…”

Section: Discussionmentioning

confidence: 88%

Sedimentary architecture and glacial hydrodynamic significance of the stratified Oak Ridges Moraine, southern Ontario, Canada

Sharpe

Russell

2023

Boreas

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High-quality subsurface data provide new insights into the formation of Oak Ridges Moraine (ORM), an ~80 km 3 sequence of stratified meltwater deposits resting >200 m above adjacent Lake Ontario. The ORM sedimentary succession comprises a three-part regional architecture: (i) ~north-south channel sand-gravel; (ii) channel-capping rhythmites; and (iii) east-west ridge sediments. The ORM depositional sequence overlies a regional unconformity with a cross-cutting channel network resulting from ~north-south meltwater floods that transitioned progressively (falling stage) from a ~NNE to ENE flow direction (parallels Lake Ontario depression). Seismic profiles delineate the channels and channel fill characteristics of bank-to-bank channel sedimentation of thick gradational gravel-sandmud sequences. Channel-capping mud (~100-236 rhythmites) within multiple channels beneath the ORM landform mark a widespread interval of low-energy, seasonally controlled subglacial pond deposition. During this quiescent period ice-sheet thickness adjusted to flood-induced stretching/thinning and re-profiled slopes. New ice gradients led to east-west flow and deposition of the overlying third element, a sequence of high-energy confined esker-fan sediments along ORM ridge. Close, sequential timing (~329 varve years) of channel, basin and ridge-forming architectural elements supports naming this assemblage the ORM formation. Proposed ORM floods are analogous to Icelandic j€ okulhlaups based on the size, geometry and sedimentology. The observed rhythmite interval between flood events represents a short period (~236 years) of regional meltwater storage prior to east-west ORM flooding. The ORM channel and overlying esker-fan sediment ridge represent two closely timed meltwater drainage events rather than formation by coalescing ice streams. The scale and timing of the ORM flood events are linked to rapid sea-level rise, ~13.5 ka BP. This high-resolution ORM sedimentological record may provide insights into depositional and glaciogenic controls of other large, stratified moraines. The ORM data indicate deposition in response to hydrodynamic events (outbreak floods, re-profiled ice) rather than direct climate forcing.

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Section: Discussionmentioning

confidence: 88%

Sedimentary architecture and glacial hydrodynamic significance of the stratified Oak Ridges Moraine, southern Ontario, Canada

Sharpe

Russell

2023

Boreas

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“…We are very grateful to Russell (2019) for the opportunity to expand on the significance of ice streaming in Southern Ontario at the end of the last glaciation and to place that work in a broader glacial geological context of what is known of the paleoglaciology of former ice sheets. Taylor (1913) is credited with recognizing the interlobate origin of the Oak Ridges Moraine (ORM), which has long been accepted (see Barnett 1992;Barnett et al 1998 and many references therein).…”

Section: Shane Sookhan Nicholas Eyles and Lina Arbelaez-morenomentioning

confidence: 99%

Reply to the comment by H.A.J. Russell on “Converging ice streams: a new paradigm for reconstructions of the Laurentide Ice Sheet in southern Ontario and deposition of the Oak Ridges Moraine”

2019

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Converging ice streams: an unreasonable hypothesis for deposition of the Oak Ridges Moraine, southern Ontario

Sharpe

Russell

2020

Can. J. Earth Sci.

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The hypothesis that Oak Ridges Moraine (ORM) formed between converging ice streams requires critical testing. Available data (e.g., digital elevation models, maps, seismic profiles, continuous cores, and pit exposures) are inconsistent with the converging ice stream hypothesis. Combined analysis of landform and subsurface data permits testing the ORM area stratigraphic sequence and sedimentary origin. Stratigraphic data indicate that drumlinized Newmarket Till, incised by north–south-oriented (tunnel) valleys, extends beneath ORM. Thus, streamlining on Newmarket Till is older than ORM and has no direct bearing on its formation. The north–south-trending valleys truncate streamlined Newmarket Till, extend to bedrock, have inset eskers, and occur beneath ORM. Hence, these valleys are older than ORM and have a subglacial rather than a proglacial origin. Overlying the mega-scale lineations and incised channels are topographically elevated (>300 m a.s.l.), ORM glaciofluvial–glaciolacustrine sequences. Its east to west paleoflow trend indicates an east–west-oriented hydraulic gradient, orthogonal to expected gradients of proposed north-south converging ice streams. The exclusive presence of ORM meltwater sediments, with rare deformation, is incompatible with a converging ice stream, deforming-bed hypothesis. Halton sediment grades upward from stratified sand (ORM) to interbedded diamicton and glaciolacustrine sediment, rather than deformation till. Halton sediment overlies ORM and consequently the proposed Halton ice streaming is younger than the moraine. Halton Till is present in few of the predicted ice stream areas, and where Halton Till is present, it has no mega-scale lineations. In sum, the weight of evidence unequivocally argues against a converging ice-stream process model for the ORM.

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Comment on “Converging ice streams: a new paradigm for reconstructions of the Laurentide Ice Sheet in southern Ontario and deposition of the Oak Ridges Moraine”

Cited by 3 publications

References 29 publications

Sedimentary architecture and glacial hydrodynamic significance of the stratified Oak Ridges Moraine, southern Ontario, Canada

Sedimentary architecture and glacial hydrodynamic significance of the stratified Oak Ridges Moraine, southern Ontario, Canada

Reply to the comment by H.A.J. Russell on “Converging ice streams: a new paradigm for reconstructions of the Laurentide Ice Sheet in southern Ontario and deposition of the Oak Ridges Moraine”

Converging ice streams: an unreasonable hypothesis for deposition of the Oak Ridges Moraine, southern Ontario

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