Abstract
Grain-shape analyses are essential in geological research because they provide the basis for genetic interpretations, including sedimentation conditions. The methods of visual evaluation used so far have been subjective, time-consuming and labour intensive. Automatic particle image analysis, including the methods used by the Morphology G3SE device, open up the possibility of mass and objective roundness analysis of mineral and organic particles. The article presents the results of measurements for the grain scale proposed by Krumbein in 1941, as this scale has been used in numerous sedimentological studies. The standard shapes were analysed using four parameters: High Sensitivity (HS) Circularity, Convexity, Solidity and Aspect Ratio. In the discussion, both the results and the grain-shape standards were critically assessed. The most important trends in the distribution of morphometric parameters of the scale are shown. On this basis, it was found that it is impossible to determine the parameter boundary values that would distinguish each class of grain roundness proposed by Krumbein. The conclusions propose criteria for the automatic differentiation of angular, subrounded and rounded grains, which could be a basis for describing the shape of mineral particles.
Highlights
Kristina Pikelj and Mavro LučićGeological textural analyses consist of determining grain size and shape
The high similarity of the values of the morphometric parameters examined for standard grains from different classes leads to a critical approach to classifying the roundness classes proposed by Krumbein [4]
The main reason is that the automatic measurement results showed a very high similarity between the parameters of standard grains belonging to different classes, neighbouring and distant ones
Summary
Geological textural analyses consist of determining grain size and shape. Fundamental in studying sedimentation environments [1], is determined using many methods and measurement techniques. These include methods based on both grainshape measurements [2,3] and visual evaluation, as proposed by Krumbein [4], Powers [5]. Textural maturity of sediments depends on the shape of grains [18]. This shape, depends on the characteristics of the source material and the transport distance [7,19,20]. It should be emphasised that grain shapes in various sedimentary environments are similar, especially fluvial, aeolian and beach sediments, as well as glacial and weathered [14,19]
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