Till‐forming processes beneath parts of the <scp>C</scp>ordilleran <scp>I</scp>ce <scp>S</scp>heet, <scp>B</scp>ritish <scp>C</scp>olumbia, <scp>C</scp>anada: macroscale and microscale evidence and a new statistical technique for analysing microstructure data

Neudorf, Christina M.; Brennand, Tracy A.; Lian, Olav B.

doi:10.1111/bor.12009

Cited by 16 publications

(9 citation statements)

References 103 publications

(293 reference statements)

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“…3 to 9 and 11 to 15) and quantitative data for the clast microfabrics (rose diagrams on Figs. 3 to 9 and 11 to 15) developed within the diamicton layers were obtained using the methodology of (also see Vaughan-Hirsh et al, 2013;Neudorf et al, 2013). This microstructural mapping approach was used alongside existing methods of analysis resulting in the detailed microstructural and sedimentological analysis of the glacigenic sediments exposed at both sites.…”

Section: Location Of Study Areas and Methodologymentioning

confidence: 99%

“…The dilation of water-saturated subglacial sediments is thought to facilitate ductile bed deformation (e.g. Murray and Dowdeswell, 1992;van der Meer et al, 2003;Evans et al, 2006;Menzies 2012;Neudorf et al, 2013), with this process leading to the weakening of the till by lowering the effective normal stress (i.e. the difference between ice overburden pressure and porewater pressure; Piotrowski et al, 2004;Menzies and Ellwanger, 2010).…”

Section: Formation Of a Finescale Stratification Within Subglacial DImentioning

confidence: 99%

“…However, the development of such structures can be strongly lithologically controlled (e.g. microshears defined by a unistrial plasmic will only form in clay-rich sediments) and their identification is considered to be qualitative and potentially subjective (Leighton et al, 2012;Neudorf et al, 2013). As a result a reliable method of estimating shear strain from thin sections of deformed glacial sediments is yet to be established.…”

Section: Conceptual Model Involving Liquefaction Injection Sedimentmentioning

confidence: 99%

“…Micromorphology is increasingly being used by glaciologists and Quaternary geologists as a primary tool for the analysis of subglacial sediments as the technique can provide far greater detail of the depositional and deformation histories recorded by these sediments than can be obtained from macro-scale studies alone (see Menzies and Maltman, 1992;van der Meer, 1997;Menzies et al, 1997;Khatwa and Tulaczyk, 2001;van der Meer et al, 2003;Roberts and Hart, 2005;Hiemstra et al, 2005;Evans et al, 2006;Baroni and Fasano, 2006;Larsen et al, 2006Larsen et al, , 2007Neudorf et al, 2013). In particular, this approach has been used to unravel the often complex deformation histories recorded by glacigenic sequences (van der Meer, 1993;Phillips and Auton, 2000;van der Wateren et al, 2000;Menzies, 2000;Phillips et al, 2007;Lee and Phillips, 2008;Denis et al, 2010;Vaughan-Hirsch et al, 2012;Narloch et al, 2012Narloch et al, , 2013 as well as investigate the role played by pressurised melt water during these deformation events (Hiemstra and van der Meer, 1997;Phillips and Merritt, 2008;van der Meer et al, 2009;Denis et al, 2010;Phillips et al, 2012;Narloch et al, 2012Narloch et al, , 2013.…”

Section: Introductionmentioning

confidence: 99%

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Micromorphological evidence of liquefaction, injection and sediment deposition during basal sliding of glaciers

Phillips

Lipka

Meer

2013

Quaternary Science Reviews

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The sliding of an ice mass over its bed represents one of the main mechanisms for the forward motion of glaciers and ice sheets, facilitated by the periodic introduction of meltwater along the ice-bed interface or regelation of the overriding ice. In the geological record, however, physical evidence of this process having occurred beneath former ice masses is apparently limited. This paper presents the results of a detailed micromorphological study of thinly stratified subglacial tills exposed at two sites: (i) Galmis in Switzerland and (ii) Plumpe Farm, near Gretna in SW Scotland. The stratification within these tills comprises alternating layers of massive to weakly foliated diamicton and variably deformed (folded, faulted) laminated silt and clay. Microtextural and microstructural evidence is interpreted in terms of repeated phases of basal sliding as the ice overrode a soft-sediment bed. Elevated meltwater contents/pressures encountered immediately prior to, and during basal sliding promoted localised liquefaction within the bed. Decoupling of the ice mass from its bed enabled the injection of the liquefied diamicton along the ice-bed interface and/or into the laminated sediments immediately adjacent to this boundary. The laminated silts and clays record the settling out of fines (clay, silt) from meltwater trapped along the ice-bed interface after an individual phase of basal sliding has ceased. Injection of till into the locally water saturated silts and clays resulted in partial liquefaction and incomplete mixing of these finegrained sediments with the diamicton. Density contrasts between the two liquefied sediments led to the development of a complex 'vinaigrette-like' texture comprising rounded to irregular till pebbles within a matrix of variably homogenised silty clay. Recoupling of the ice with its bed led to localised folding and thrusting within the laminated silts and clays, hydrofracturing and injection of a network of sand-filled veins, and the imposition of a variably developed clast microfabric in the diamicton layers. Analysis of the clast microfabrics indicates that the intensity of these fabrics is highly variable reflecting the variation in the intensity of deformation imposed by the overriding ice.

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Section: Location Of Study Areas and Methodologymentioning

confidence: 99%

Section: Formation Of a Finescale Stratification Within Subglacial DImentioning

confidence: 99%

Section: Conceptual Model Involving Liquefaction Injection Sedimentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Micromorphological evidence of liquefaction, injection and sediment deposition during basal sliding of glaciers

Phillips

Lipka

Meer

2013

Quaternary Science Reviews

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“…; Neudorf et al . ). The issue of interpreting three‐dimensional structures from a two‐dimensional slice through a sample block, and the potential impact on turbate dimension measurements in this study, therefore still merits brief discussion.…”

Section: Turbate Features and Their Observation In Thin Sectionmentioning

confidence: 97%

Quantification of turbate microstructures through a subglacial till: dimensions and characteristics

Lea

Palmer

2014

Boreas

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Despite extensive study and debate regarding the significance of turbate (also known as 'rotational') microstructures in glacially deformed sediments, characteristics regarding the dimensions of these features remain unresolved. This study presents the first explicitly quantitative measurement and analysis of turbate microstructure dimensions, and their relation to till texture through thin section analysis. Samples were taken from coarseresolution horizontal and vertical transects of a macroscopically homogenous subglacial till, with subset areas of each thin section (30 mm 2 ) analysed. The frequency and apparent a-axes and b-axes of both coreless and cored turbate structures (and their corestones) were measured, and simple univariate statistical methods used to establish the (in-)variability of these dimensions through the till profile. Summarizing findings, (i) the dimensions of both cored and coreless turbate populations display log-normal distributions when all measurements are analysed together, although not all individual sample populations possess these same distributions; (ii) turbate dimension populations are inconsistent within a sample block, precluding evaluation of turbate variability through a profile from single thin sections; (iii) analysis of turbate morphology and variability provisionally indicate that the three-dimensional structure of turbates are likely to be cylindrical or flared, while weak relationships are also observed amongst till texture, turbate dimensions and frequency.

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2017

Till: A Glacial Process Sedimentology

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Till‐forming processes beneath parts of the Cordilleran Ice Sheet, British Columbia, Canada: macroscale and microscale evidence and a new statistical technique for analysing microstructure data

Cited by 16 publications

References 103 publications

Micromorphological evidence of liquefaction, injection and sediment deposition during basal sliding of glaciers

Micromorphological evidence of liquefaction, injection and sediment deposition during basal sliding of glaciers

Quantification of turbate microstructures through a subglacial till: dimensions and characteristics

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