ABSTRACT

Particle size analysis is one of the potentially most powerful tools available for the interpretation of any population of sedimentary particles. The size distribution characterizes the particles as a product, providing information on the actual particle sizes, and also is a prerequisite to understanding their roles in a set of sedimentary processes. Fine-grained suspended sediments are the least amenable to size analysis because of the difficulty of preserving the natural state of aggregation throughout sampling and analysis.

Fine suspended sediments are composed of inorganic mineral matter and living and dead organic matter which occur as individual particles, and as agglomerates and aggregates. The projected areas, volumes, and diameters of the particles are highly variable as are their electrical and optical properties. The various methods of size analysis measure very different properties of the particle population. The basic methods of sizing fine suspended sediments described in this paper are microscopic analysis, optical-sedimentation analysis, direct optical analysis, and electronic (Coulter Counter) analysis.

The microscopic method is the only one which permits direct visual observation of the particles, but yields a number frequency distribution rather than a weight or volume-size distribution. Optical-sedimentation methods permit analysis of the hydraulic behavior of the sediment in its natural medium, but at present are limited by concentration and size range. The Coulter Counter method is in some respects the most versatile method, but it yields a volume distribution which can not be directly related to settling velocity.