GRAIN-SIZE CHARACTERISTICS OF FINE-GRAINED UNFLOCCULATED SEDIMENTS .1. ONE-ROUND DISTRIBUTIONS

A simple physical model of gravitational settling from an unsorted, un flocculated source suspension is presented and an equation derived to describe the grain-size spectra of the resulting bottom sediment. Resu lts of grain-size analyses of sediments from a variety of environments and geographical locations are shown to conform with the postulated m odel. The characteristic size spectrum, termed 'one-round' sediment, i dentifies a deposit which has settled from suspension with no subseque nt reworking resulting in modification of the grain-size distribution. The distribution of settling rates of grains in the suspension may be inferred from an analytical form fit to the bottom sediment grain-siz e spectrum, along with knowledge of certain physical characteristics o f the fluid (e.g. mean velocity profile).