Architectural element analysis applied to glacial deposits: Internal geometry of a late Pleistocene till sheet, Ontario, Canada

Boyce, Joseph I.; Eyles, Nicholas

doi:10.1130/0016-7606(2000)112<98:aeaatg>2.0.co;2

Cited by 115 publications

(73 citation statements)

References 40 publications

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“…However, the distribution of thick till probably also partially reflects infilling of the pre-existing topography (e.g. Boyce and Eyles, 2000), since the buried glaciofluvial deposits tend to be preserved in bedrock depressions. Assuming the buried glaciofluvial deposits are correlative with the Cadder Sands and Gravel Formation (Table 1), the overlying till package in those areas can be considered wholly a product of the lastglacial cycle.…”

Section: D Geological Modelling Resultsmentioning

confidence: 99%

Ice dynamics and sediment movement: last glacial cycle, Clyde basin, Scotland

Finlayson

2012

J. Glaciol.

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ABSTRACT. The nature and behaviour of sediment beneath glaciers influences how they flow and respond to changing environmental conditions. The difficulty of accessing the bed of current glaciers is a key constraint to studying the processes involved. This paper explores an alternative approach in which accessible sediments under the beds of former mid-latitude ice sheets are examined and related to changing ice behaviour during a glacial cycle. The paper focuses on the partly marine-based Pleistocene British Ice Sheet in the Clyde basin. A three-dimensional computation of subsurface glacial sediment distribution is derived from 1260 borehole logs. Sediment distribution is linked to an empirically-based reconstruction of ice sheet evolution, permitting identification of distinctive phases of sedimentation. Maximum sediment mobilisation and till deposition (<0.04 m a -1 ) occurred during ice advance into the basin from adjacent uplands. Subglacial processes were influenced locally by the relative stiffness of pre-existing sediments, the permeability of the sub-till lithology, and topography; the resulting mean till thickness is 7.7 m with a high standard deviation of 7.0 m. In places, focused till deposition sealed pre-existing permeable substrates, promoting lower effective pressures. Sediment remobilisation by meltwater was a key process as ice margins retreated back through the basin, upon deglaciation.

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Section: D Geological Modelling Resultsmentioning

confidence: 99%

Ice dynamics and sediment movement: last glacial cycle, Clyde basin, Scotland

Finlayson

2012

J. Glaciol.

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“…Basal tills may be generated by different processes such as lodgement (Dreimanis, 1989;Ruszczynska-Szenajch et al, 2003), melt-out (Shaw, 1982;Clayton et al, 1989;Piotrowski, 1992) and sediment deformation by either ploughing (Clark and Hansel, 1989;Tulaczyk et al, 2001;Clark et al, 2003;Iverson and Hooyer, 2004) or subglacial deformation (Boulton and Jones, 1979;Alley, 1991;Boyce and Eyles, 2000), or a hybrid of the above processes (Benn and Evans, 1996;Piotrowski et al, 2006). Which process is the dominant one is, however, often contentious-especially in the case of macroscopically massive tills, which are widespread in formerly glaciated areas (e.g.…”

Section: Introductionmentioning

confidence: 99%

Microstructural evidence of low‐strain, time‐transgressive subglacial deformation

Larsen

Piotrowski

Menzies

2007

J Quaternary Science

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Microstructural analyses were used to investigate the formation of a macroscalemassive till at Knud Strand in Denmark. More than 100 thin sections were examined and microstructures mapped and counted for quantitative comparison and interpretation. Microstructures indicative of both brittle (grain lineations, edge-to-edge crushed grains) and ductile (turbate structures) deformation are evenly distributed in vertical profiles through the till, suggesting that strain contributed to its formation. Discrete shears (grain lineations and plasmic fabric) probably accommodated most deformation, whereas rotational deformation was less prominent. The microshear geometry fits the predicted Coulomb-Mohr failure criterion, indicating that till behaves as a plastic material. Strain estimate of ca. 10 1 from micromorphological proxies is two-three orders of magnitude lower than expected if the till was subjected to pervasive deformation. A hybrid of lodgement and time-transgressive deformation is envisaged as the till-forming processes. Our data suggest that even abundant evidence of microscale deformation at continuing high levels of strain may only record the latest process of deposition and deformation and therefore not fully reflect the complexity of till genesis.

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“…13h). Recent studies in the Toronto area suggest that, locally, the ice flowed initially from the southeast out of the Ontario basin (Mahaney et al 2014), followed by more regional southerly flow and a late-stage shift to northwest-flowing ice during deglaciation (Boyce and Eyles 2000;Maclachlan and Eyles 2013).…”

Section: Regional Correlations and Implications For Ice Sheet Reconstmentioning

confidence: 99%

The pre-Late Wisconsin stratigraphy of southern Simcoe County, Ontario: implications for ice sheet buildup, decay, and Great Lakes drainage evolution

Mulligan

Bajc

2018

Can. J. Earth Sci.

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Recent three-dimensional mapping investigations in southern Simcoe County, Ontario, allow refinement of the existing regional stratigraphic framework. Analysis of 25 continuously cored boreholes has revealed a complex but consistent sediment succession that provides a record of the last two glacial cycles (Marine Isotope Stages 1-6). Five stratigraphic units (SU1-SU5) comprise the pre-Late Wisconsin record. The stratigraphy is floored by a presumed Illinoian glacial complex consisting of a lower, coarse-grained till (SU1), locally overlain by stratified glaciolacustrine and glaciofluvial sediments (SU2), but more commonly capped by a stone-poor, fine-grained till (SU3) of the Georgian Bay lobe. A widespread subaerial unconformity developed on the upper surface of SU3 contains organic-bearing, nonglacial deposits (SU4) ranging between 54 800 ± 3000 years BP (considered beyond the limits of radiocarbon dating) and 37 450 ± 590 14 C years BP. SU4 is abruptly overlain by a thick succession of rhythmically laminated lacustrine muds graded upwards into glaciolacustrine silts and clays interrupted by regionally continuous sand bodies (SU5). The succession is capped (and locally truncated) by Late Wisconsin Newmarket Till. The sedimentary record of southern Simcoe County is correlated with other well-studied reference sections in southern Ontario and contains information that informs reconstructions of former ice extents in the lower Great Lakes region following the Illinoian glaciation. Several sediment units host aquifers, but limited thickness and spatial extent, as well as issues with naturally occurring dissolved gases and solids, restrict their use for groundwater supply.Résumé : Des études cartographiques tridimensionnelles récentes dans le sud du comté de Simcoe, en Ontario, permettent de peaufiner le cadre stratigraphique régional existant. L'analyse de 25 forages carottés en continu révèle une séquence sédimen-taire complexe mais cohérente qui offre un profil des deux derniers cycles glaciaires (étages 1-6 de la stratigraphie isotopique marine). Cinq unités stratigraphiques (SU1-SU5) renferment le profil pré-wisconsinien tardif. La base de la coupe stratigraphique est un complexe glaciaire d'âge illinoien présumé consistant en un till inférieur à grains grossiers (SU1) sur lequel reposent localement des sédiments glaciolacustres et fluvioglaciaires stratifiés (SU2), mais qui est plus couramment recouvert d'un till à grains fins pauvre en pierres (SU3) du lobe de la baie Georgienne. Une discordance subaérienne répandue formée sur la surface supérieure de SU3 contient des dépôts non glaciaires contenant de la matière organique (SU4) allant de 54 800 ± 3000 années BP (considéré comme étant hors des limites de la datation au radiocarbone) à 37 450 ± 590 14 C années BP. SU4 est abruptement recouverte par une épaisse séquence de boues lacustres à laminations rythmiques passant vers le haut à des silts et des argiles glaciolacustres interrompus par des corps de sable d'ampleur régionale (SU5). La séquence e...

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Architectural element analysis applied to glacial deposits: Internal geometry of a late Pleistocene till sheet, Ontario, Canada

Cited by 115 publications

References 40 publications

Ice dynamics and sediment movement: last glacial cycle, Clyde basin, Scotland

Ice dynamics and sediment movement: last glacial cycle, Clyde basin, Scotland

Microstructural evidence of low‐strain, time‐transgressive subglacial deformation

The pre-Late Wisconsin stratigraphy of southern Simcoe County, Ontario: implications for ice sheet buildup, decay, and Great Lakes drainage evolution

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