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Carbonate sands are composed of relatively few particle types (e.g., Halimeda, coralline algae, corals, mollusks, and foraminifera). The shape of a particular sand grain is highly dependent on the particle type of which it is composed. Previous, studies of modern carbonate environments show that the composition of sand substrates from different subenvironments are dependent on the organisms that inhabit them. These depositional environments can thus be distinguished from each other according to their constituent particle compositions and, therefore, also by analysis of particle shapes.
Template (shape) matching can be accomplished only after the digitized shapes have been normalized to a unit-sized circle and registered. Registration involves the simple computation of shape-specific points within, on, or near the 2-dimensional contour of the sand grain. Shapes are subsequently rotated so that all of the shapes are in a similar position relative to their shape-specific points, allowing more meaningful comparisons between particles. After registration, 36 equi-angular radial lengths are calculated for grain from the center of mass to the boundary outline. A template-matching algorithm was devised in order to determine the relative percentages of several reference shape types, representing the constituents contained within 35 samples from 4 carbonate beaches and associ ted subtidal environments from the Florida Keys. Reference shapes may be chosen arbitrarily or obtained by computing average shapes of the various constituents. The precision of the shape classifications may be enhanced by adding supplemental reference shapes to the algorithm.
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