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

James Lea, Adrian Palmer

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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 coarse-resolution horizontal and vertical transects of a macroscopically homogenous subglacial till, with subset areas of each thin section (30 mm2) 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.
Original languageEnglish
JournalBoreas: an International Journal of Quaternary Research
Early online date11 Mar 2014
Publication statusPublished - 11 Mar 2014

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