A note on granulometric sand types andthe Wentworth classification

摘要

Granulometric sand types are characterized by their typical grain-size frequency distributions plotted as the first differentials of the cumulative distributions at the ψ-scale. In all deserts, past and present, there seem to exist only about a dozen granulometric sand types. They belong to a system of the granulometric evolution of aeolian sands and as such can pro-vide valuable information on the history of sand seas and dunefields. In many papers, how-ever, not the ψ-scale but various modifications of the Wentworth classification are used. It is attempted to find rules for the transformation of the granulometric sand types into modified Wentworth classifications. The granular overlap between the corresponding sieving fractions was found to be most decisive. As a consequence, the granulometric sand types at the begin-ning and at the end (residuals) of the sequences of the granulometric evolution can well be identified. The history of older barchan dunes may also be studied comparably. Some major granulometric sand types, however, cannot be identified with certainty. The use of ψ-gauged sieving sets is strongly recommended.