QUANTIFYING PARTICLE SHAPE BY IMAGE ANALYSIS: APPLICATION TO NATURAL SEDIMENT SAMPLES IN VARIOUS CLIMATE SYSTEMS
Samples were collected from fluvial systems in four contrasting climates: hot-arid (southeastern California), hot-humid (eastern Puerto Rico), cold-arid (proglacial streams of the Dry Valleys, Antarctica), and cold-humid (Austerdalen proglacial stream, Norway). Samples were collected at regular intervals along the fluvial/alluvial transects beginning at the headwaters and extending ~15 km downstream. Samples were processed to remove carbonate and organic matter, and sieved to isolate various size fractions. Mud and sand samples were analyzed using the Malvern Morphologi3 instrument— a microscope system that enables static image analysis of hundreds to thousands of individual particles. This instrument captures 2D images, so provides information on size parameters such as circle-equivalent diameter, length, width, perimeter, and area, as well as shape parameters such as circularity and convexity. We compared given size fractions from different climates, and compared proximal-medial-distal samples from individual climates. Results provide quantitative constraints on shape differences that relate to climate and transport, even for very fine-grained sand and mud size fractions. For ancient sedimentary rocks that can be effectively disaggregated for particle shape analysis, this approach could provide insight on paleoclimatic interpretations.