This function plots sand, silt and clay fraction data on a ternary plot that is marked with the Shepard classification scheme labels from his article:
Shepard, F.P., 1954, Nomenclature based on sand-silt-clay ratios: Journal Sedimentary Petrology, v. 24, p. 151-158.
This function is merely a modification of the Ternplot function available on the Mathworks site authored by Carl Sandrock (20020827).
To use the function, type
where the sand, silt and clay fractions are given by column vectors. The fractions can be given either in % (0 to 100), or as a unitless fraction (0 to 1).
For each point, the data are normalized to insure they sum to 100%. If the data contain <10% gravel, the remaining sand, silt and clay fractions can be given to the Shepard function, and they will be renormalized and treated as though there were no gravel present. If the data contain more than 10% gravel, the Shepard plot should not be used. The ternary plot designed by Schlee should be utilized instead:
Schlee, J., 1973, Atlantic continental shelf and slope of the United States - sediment texture of the northeastern part: U.S. Geological Survey, Professional Paper 529 - L, 64 p.
This version updates the U.S. Geological Survey disclaimer.