Scanning Electron Micrographs of Quartz Sand Grains from Cold Environments Examined Using Fourier Shape Analysis

Abstract

ABSTRACT The use of grain shape to identify sedimentary environments assumes that grain morphology reflects environmental history. Scanning electron microscopy permits detailed examination of quartz sand grain surface morphology. Particle shape from gross form to surface texture is quantified using closed-form Fourier analysis of whole grain outlines from micrographs of 158 quartz sand grains representing subglacial transport and subaerial weathering in cold environments. Mean harmonic amplitude spectra and roughness coefficients are calculated, and three problems are investigated yielding the following results. Findings are preliminary due to the relatively small number of grains analyzed. 1) Two-dimensional particle micrographs are a suitable surrogate for three-dimensional grain roundness a d texture. 2) The particle size of a sand grain sample affects its roundness and texture, and only samples of similar size range should be compared. 3) Fourier shape analysis distinguishes significant differences between basal and englacial grains, the latter being more angular and rough in texture. This finding is relevant to the definition of debris transport paths through glaciers. The technique may also prove useful in the interpretation of marine sediments from cold regions, and pre-Quaternary diamictites of controversial or unknown origin.