The observation of clayey matrix on a thin-section under polarized transmitted light allows the analysis of the clay particle arrangements, the measurement of their orientations in 3-D, and finally the cartography of the different orientation modes by using a simple image analysis system connected to the optical microscope. The method is based on: (1) the analysis of the shape evolution of the grey-level diagram vs. the rotating stage angles; and (2) the mathematical decomposition of these grey-level diagrams into elementary gaussian curves. For each identified orientation mode, the standard deviation of the grey values gives the dispersion index of the oriented particles around the axial plane. The 3-D representation is performed on the Wulff stereonet. The horizontal orientations are measured by simple rotation of the revolving stage and the dip angles are deduced from the peak displacements along the abscissa of the grey-level diagram during the complete rotation of the revolving stage. The quantifications (percentage, isotropy and distribution index) are performed after a thresholding operation of each orientation mode.

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