How are the outputs for the grain-size fractions of gravel, sand, and mud extracted?
Many data sets contain these values (based on Wentworth scale), and in those cases, the values are passed through to extracted (EXT) output. In some cases the data are presented in the form of a detailed grain-size analysis such as at 1/2 phi intervals. dbSEABED assembles grain size analysis streams into G:S:M fractions by assigning each analysis class to its fraction (or proportioning if the class straddles a fraction boundary). Note: Many grain size analyses techniques range only through sand and mud, while gravel is not analysed. In these cases the database reports the gravel percent as null in outputs.
