Sedimentologists study how particles are transported and deposited on the surface of the earth. Some use this information to make sediment transport predictions, others to interpret the depositional history of an ancient deposit. An important part of the sediment transport problem is the determination of the size distribution of grains. Grain size methods are based on the premise that the population of particles being analyzed behave as discrete entities and do not react with each other during their sizing. These same methods also assume that the sample being analyzed is a true representation of the parent population. In other words, particle–particle interactions have not been altered from the natural environment, during or subsequent to collection of the sample. Samples from some sedimentary environments, such as sand grains collected on an active beach, can provide an unbiased estimate of the size characteristics of the parent population.

Chapter 3 has already introduced readers to the concept that many sedimentary environments have grains in transport, not as single grains but in clusters of other particles. Pretreatments may alter and bias the laboratory-produced particle size distribution. Such results provide better information on the size of particles that comprise the aggregates.

For marine sedimentary environments, the act of collecting suspended particles may alter the in situ particle–particle bonding; typically, particle size is decreased. Recent progress has been made on the determination of particle size within the hydrodynamic environment.