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TitleSedimentary architecture and glacial hydrodynamic significance of the stratified Oak Ridges Moraine Formation, southern Ontario, Canada
AuthorSharpe, DORCID logo; Russell, H A JORCID logo
SourceBoreas 2023 p. 1-40, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20220056
PublisherJohn Wiley & Sons Ltd
Mediapaper; digital; on-line
File formatpdf
NTS30; 40; 31C; 31D; 31E; 31F; 41A; 41H
AreaLake Ontario
Lat/Long WENS -82.0000 -76.0000 46.0000 42.0000
Subjectssedimentology; moraines; seismic profiles; subsurface geology; seismic data; digital terrain modelling; landforms; hydrodynamics; Oak Ridges Moraine
Illustrationslocation maps; digital elevation models; stratigraphic columns; seismic reflection profiles; seismic profiles; tables; isopach maps; core logs; photographs
ProgramGroundwater Geoscience Archetypal Aquifers of Canada
Released2023 02 23
AbstractHigh-quality subsurface data provide new insights into the formation of Oak Ridges Moraine (ORM), an ~80 km3 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) froma ~NNEtoENEflowdirection (parallels Lake Ontario depression). Seismic profiles delineate the channels and channel fill characteristics of bank-to-bank channel sedimentation of thick gradational gravel-sand- mud sequences. Channel-cappingmud (~100-236 rhythmites) withinmultiple channels beneath theORMlandform 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.Newice 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 supportsnamingthisassemblage theORMformation.ProposedORMfloods areanalogousto 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 theORMflood 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.
Summary(Plain Language Summary, not published)
Sedimentary architecture and glacial hydrodynamic significance of the stratified Oak Ridges Moraine Formation, southern Ontario, Canada Large stratified moraines, composed of sorted sand and gravel, are sporadic yet remarkable features on the Canadian landscape. They are poorly described and understood, yet they can help us understand how the glaciers wasted away, and their importance as aquifers and to mineral exploration. Detailed 3D studies of the Oak Ridges Moraine (ORM) serve as a model of this and other stratified moraines. Resultant high-resolution models are aiding land and water resource planning in the Greater Toronto area. The central problem of how to build up a significant focused volume/thickness of stratified sediment relates to their formation as exceptional glacial floods such as have occur recently in Iceland. The ORM ice-age floods were much bigger and deposited ~80 cubic kms of sand and gravel in ~500 years. The scale and timing of the ORM flood events are linked to rapid sea level rise, ~13,500 years before present.

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