ABSTRACT
Certain properties of sediments are basic and common to many of the topics in the remainder of this book and are presented here. In Sections 2.1, 2.2, and 2.3, essential characteristics of individual sedimentary particles (particle size, settling speed, and mineralogy) are described. Although individual particles are the basic building blocks for suspended as well as bottom sediments, sedimentary particles generally do not exist in the form of isolated particles. In the overlying water, finer-grained particles are generally present as aggregates of particles, that is, as flocs; in contrast, coarser-grained particles usually do not aggregate and are present as individual particles. Properties of a floc, such as size and density, are often significantly different from those of the individual particles making up the floc. An introduction to flocculation and the properties of flocs is given in Section 2.4. As the suspended particles or flocs settle out of the overlying water, they are deposited on the sediment bed, where they may be buried by other depositing particles. As this occurs, flocs are compressed and formed into larger and denser aggregates. Due to the weight of the overlying sediments, interstitial water and gas are forced out from between the solid particles/aggregates in the sediment bed and are transported toward the sediment-water surface; differential settling and transport of different size particles may also occur. In addition, gas may be generated within the sediments due to the decay of organic matter. The bed consolidates with time due to these processes and also due to chemical reactions in the bed. In Section 2.5, procedures for measuring the bulk densities of these bottom sediments are discussed, and illustrations of the variations of bulk densities with depth and time are given.
