A VISUAL BASIC PROGRAM TO CLASSIFY SEDIMENTS BASED ON GRAVEL-SAND-SILT-CLAY RATIOS

Nomenclature describing size distributions is important because grain size is the most basic sediment attribute. Therefore, to facilitate generation of standard nomenclature, we have written a computer program (SEDCLASS) to classify sediment grain-size distributions based on relationships between size fractions. Our program runs on Windows computers and allows users to select options with mouse-click events and interactive dialogue boxes. The program also permits users to select output in either the Shepard (1954) or Folk (1974) classification schemes, the two most common schemes used by sedimentologists. Briefly, Shepard's classification scheme emphasizes ratios of sand, silt, and clay because they reflect sorting and reworking; Folk's scheme stresses gravel because of its relation to highest current velocity during deposition, together with the maximum grain size of available detritus. Detailed schematics of these schemes and documentation are available within the program.

Input files 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 in the requested destination directory and allows the user to view results in a display window to determine whether errors have occurred. The output file will also have a header for its first line, but will now have eight fields; the original fields plus an additional field for sediment classification in the desired scheme. The software and documentation are available free of charge.