PROCEDURES

Introduction

Grain size is the most fundamental property of sediments. Geologists use information on sediment grain size to study trends in surface processes related to the dynamic conditions of transportation and deposition, ecologists use it when studying benthic habitats, engineers use it to study permeability and stability under load, geochemists use it to study kinetic reactions and the affinities of fine-grained particles and contaminants, and hydrologists use it when studying the movement of subsurface fluids (Blatt and others, 1972; McCave and Syvitski, 1991). Therefore, the objectives of a grain-size analysis are to accurately measure individual particle sizes or hydraulic equivalents, to determine their frequency distribution, and to calculate a statistical description that adequately characterizes the sample. Inasmuch as many geological observations consist of measurements made on a large number of specimens, the techniques and equipment used for particle-size analysis must be fast, accurate, and yield highly reproducible results.

The precision of these measurements is limited by the initial sampling techniques, conditions during storage, analytical methods, equipment, and, especially, the capability of the operator. Care and attention to detail must be exercised to achieve the best possible results. As with most types of analyses there is no ultimate technique or procedure that will produce the most precise grain size measurements for all cases. Several types of analyses have been developed over the years to accommodate the different types and sizes of samples and the scientific objectives for doing the analysis.

For many years, sand and gravel fractions were determined solely by sieve analyses, and silt and clay fractions were determined by pipette or hydrometer analyses (McCave and Syvitski, 1991) . The more recent development of rapid sediment analyzers (RSA; Ziegler and others, 1960; and Schlee, 1966), hydrophotometers, sedigraphs (Coakley and Syvitski, 1991), laser diffraction devices (Agrawal and others, 1991), and electro resistance multichannel particle size analyzers (EMPSA), such as the Coulter Counter (Milligan and Kranck, 1991), have removed much of the tedium from grain size analyses.

Measures that describe and summarize sediment grain-size information are important to geologists because of the large amount of information contained in textural data sets. With the advent of computers in the early sixties, Formula Translation (FORTRAN) programs were developed to calculate statistical parameters of geologic data (Kane and Hubert, 1962; Collias and others, 1963; Schlee and Webster, 1967). Subsequently, other particle size analysis programs were written in Algorithmic Language (ALGOL; Jones and Simpkin, 1970), Beginners All Purpose Symbolic Instruction Code (BASIC; Sawyer, 1977) for use with hand held calculators (Benson, 1981), and in Visual BASIC (Poppe and others, 2003; 2004). Early attempts to integrate computers with particle size analysis equipment began with settling tubes (Ziegler and others, 1964; Rigler and others, 1981) and EMPSAs (Muerdter and others, 1981; Poppe and others, 1985; Coulter Electronics, 1989), but software packages are now readily available for most commercial granulometric equipment.

The more recent development and commercial availability of inexpensive personal computers allows sedimentologists to construct complete computerized particle-size analysis systems (Poppe and others, 1985; Poppe and others, 2000). The major advantage of using these systems is the time-, labor-, and cost-saving functions they afford. Most of the laboratory equipment and procedures, and all of the data processing described herein may be adapted to IBM-compatible personal computers.

The purpose of this chapter is to describe and document some of the field and laboratory methods, equipment, computer hardware, and data-acquisition and data-processing software employed in the sedimentation laboratory at the Woods Hole Coastal and Marine Science Center of the U.S. Geological Survey