A VISUAL BASIC PROGRAM TO PLOT SEDIMENT GRAIN-SIZE DATA ON TERNARY DIAGRAMS

Sedimentologic datasets are typically large and are compiled into tables or databases, but pure numerical information can be difficult to understand and interpret. Thus, scientists commonly use graphical representations to reduce complexities, reveal trends and patterns in the data, and develop hypotheses. One of the most common graphical techniques used by sedimentologists is to plot the basic gravel, sand, silt, and clay percentages on equilateral triangular (ternary) diagrams. Because this means of presenting data is simple and facilitates rapid classification of sediments and comparison of samples, we have written a computer program (SEDPLOT) to produce these diagrams. Our program is written in Microsoft Visual Basic 6.0, runs on Windows 98/ME/NT/2000/XP computers, provides a window to facilitate execution, and allows users to select options primarily with mouse-click events, or through interactive dialogue boxes. The program also permits users to select both graphical and textual output in either of the two ternary schemes most commonly used by sedimentologists.

Input files to the program must be comma-delimited ASCII text and have seven fields that include: sample identifier, latitude, longitude, and percentages of gravel, sand, silt, and clay. The navigation fields may be left blank, but the remaining fields must be populated, and the sum of the percentages of gravel, sand, silt, and clay must total 100% (+/- 0.1%). The program expects the first line of the input file to be a header showing attribute names; no embedded commas are allowed in any of the data fields. Detailed error messaging warns the user of potential problems. The program generates an output file of textual equivalents in the requested destination directory and opens a second window showing the ternary diagram of the currently selected classification scheme. Buttons in the new window allow the user to toggle between classification schemes and coarse- and fine-fraction diagrams, print the plot, and show or hide sample annotation. The software with test input files, installation instructions, and documentation is available free of charge from the U.S. Geological Survey at: http://woodshole.er.usgs.gov/software/sediment-software.html