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AN OPTICAL METHOD OF MEASURING GRAIN ORIENTATION IN SEDIMENTS
Author(s) -
WINKELMOLEN A. M.,
KNAAP W.,
EIJPE R.
Publication year - 1968
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/j.1365-3091.1968.tb00852.x
Subject(s) - ellipse , optics , orientation (vector space) , eccentricity (behavior) , geology , geometry , plane (geometry) , light beam , beam (structure) , optical axis , materials science , mineralogy , physics , mathematics , lens (geology) , political science , law
SUMMARY A new method is presented for the measurement of grain orientation in clastic sediments. The method is based on the principle that when an inclined beam of light passes through an elliptical hole in a plate of a certain thickness, the amount of light passing through depends on the orientation of the long axis of the ellipse with respect to the direction of incidence of the light beam. If such a plate is rotated in its own plane, the amount of light passing through will fluctuate. Such fluctuations are larger the greater the eccentricity of the ellipse, the amount of light passed being maximal when the long axis coincides with the plane of incidence of the light. If the plate contains many holes, which need not be elliptical but for the ease of reasoning can be approximated by ellipses, their main orientation direction can be inferred from the maximum intensity of passed light. It is shown in the paper that results of a similar kind can be obtained by using a black and white picture of the grain packing in combination with a mirror. These pictures can be obtained either from thin‐sections or from printed replicas of etched polished sections of impregnated samples. The resulting data represent an integrated orientation pattern instead of a long‐axis distribution pattern as given by the grain‐by‐grain counting technique. The new method has been thoroughly checked against the visual counting method. Excellent agreement was observed.