A de-flat roundness method for particle shape quantitative characterization

Roundness is a simple but important shape characteristic. It can preserve a record of clasts wearing and deposit reworking. One of the previous methods was called percentage roundness, which could be known as the ratio of the particle’s area that holds to the area of a circle with the same perimeter Cox (J Paleontol 1(3):179–183, 1927 ). However, it is more likely expressed the degree of circularity rather than rounding due to the limit by its formula. In this paper, a new idea is proposed by modifying the percentage roundness in order to be associated with rounding more appropriately, which is called the de-flat roundness method. The method uses a de-flat algorithm based on image morphing, which is further designed to a software. The software provides the calculation of both percentage roundness and de-flat roundness. It also features other parameters like the area and perimeter of the measured one. To demonstrate its effectiveness, 81 sample grains of Krumbein’s roundness grade (J Geol 49(5):482–520, 1941 ) were measured. The correlation coefficient of de-flat roundness is 0.7183, with a 0.3416 increase than that of percentage roundness. An application of de-flat to intermittent and ephemeral braided paleochannel deposit in a Late Triassic fluvial fan from northern Junggar Basin, China, was conducted. Results show that two types of palaeoenvironment can be quantitatively distinguished by de-flat roundness, and the values match well with human perception. Therefore, de-flat method can be an effective idea in terms of roundness measurement for either geology or other research fields related to particle morphology.