Quantification of plasmic fabric through image analysis

Zaniewski, Kamil; Meer, J.J.M. van der

doi:10.1016/j.catena.2005.07.001

Cited by 24 publications

(12 citation statements)

References 5 publications

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“…Plasmic fabric develops as clay particles align in a shear zone according to the stress orientation (e.g. Maltman, 1977;Jim, 1990;Zaniewski and van der Meer, 2005). Two common types of plasmic fabric in basal tills are unistrial plasmic fabric comprising thin distinct lines of plasma orientated in one direction and lattisepic plasmic fabric consisting of preferred alignment of plasma in two perpendicular orientations (Menzies and Maltman, 1992;van der Meer, 1993).…”

Section: Plasmic Fabricmentioning

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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Section: Plasmic Fabricmentioning

confidence: 99%

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

Larsen

Piotrowski

Menzies

2007

J Quaternary Science

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“…The classification and interpretation of microstructures is a subjective exercise, and few studies have made efforts to overcome problems of subjectivity (e.g. Zaniewski & van der Meer ; Larsen et al . ; Reinardy et al .…”

Section: Methodsmentioning

confidence: 99%

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

Neudorf

Brennand

Lian

2013

Boreas

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2013 (October): 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. This paper presents the first integrated macroscale and microscale examination of subglacial till associated with the last-glacial (Fraser Glaciation) Cordilleran Ice Sheet (CIS). A new statistical approach to quantifying till micromorphology (multivariate hierarchical cluster analysis for compositional data) is also described and implemented. Till macrostructures, macrofabrics and microstructures support previous assertions that primary till in this region formed through a combination of lodgement and deformation processes in a temperate subglacial environment. Macroscale observations suggest that subglacial environments below the CIS were probably influenced by topography, whereby poor drainage of the substrate in topographically constricted areas, or on slopes adverse to the ice-flow direction at glacial maximum, facilitated ductile deformation of the glacier bed. Microscale observations suggest that subglacial till below the CIS experienced both ductile and brittle deformation, including grain rotation and squeeze flow of sediment between grains under moist conditions, and microshearing, grain stacking and grain fracturing under well-drained conditions. Macroscale observations suggest that ductile deformation events were probably followed by brittle deformation events as the substrate subsequently drained. The prevalence of ductile-type microstructures in most till exposures investigated in this study suggests that ductile deformation signatures can be preserved at the microscale after brittle deformation events that result in largerscale fractures and shear structures. It is likely that microscale ductile deformation can also occur within distributed shear zones during lodgement processes. Cluster analysis of microstructure data and qualitative observations made from thin sections suggest that the relative frequency of countable microstructures in this till is influenced by topography in relation to ice-flow direction (bed drainage conditions) as well as by the frequency and distribution of voids in the till matrix and skeletal grain shapes.

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“…Through the use of multispectral image classification, for example (see Figure 11), Zaniewski and van der Meer (2005) made an attempt to control the subjectivity in plasmic fabric analysis. It is not unlikely that the relative strength of plasmic fabricpotentially useful in the quantification of strain -is rated differently by different observers, and secondly, it is quite possible that subtle birefringence patterns go undetected due to human eyesight limitations.…”

Section: Plasmic Fabric Analysismentioning

confidence: 99%

GLACIAL LANDFORMS, SEDIMENTS | Micromorphology of Glacial Sediments

Hiemstra

2013

Encyclopedia of Quaternary Science

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Quantification of plasmic fabric through image analysis

Cited by 24 publications

References 5 publications

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

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

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

GLACIAL LANDFORMS, SEDIMENTS | Micromorphology of Glacial Sediments

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