Introduction

Over the past fifty years, the textural characterization of an unlithified sample of sandy sediment has been accomplished mainly by sieving and settling tube analysis. Both methods provide a mass frequency distribution of particle size, with the effects of particle shape and size combined. Settling tube analysis is additionally affected by particle density. Sieving became the early standard technique, accepted by both civil engineers and sedimentologists. Standard sieves were mass produced at a variety of mesh sizes, and once sieving time and tapping frequency were agreed upon, interlab precision was acceptable (<±0.25ø, where ø = −log2d and d is particle diameter in mm). Sedimentary petrologists, in their study of lithified sedimentary deposits, sized and identified sedimentary particles under a microscope using thin sections from rocks. Sieving and thin-section methods dominated sediment laboratories until the mid-1970s. With the proliferation of microcomputers in the 1980s, sieving has given way to settling tube analysis, and manual thin-section analysis has given way to image analysis.

The basic justification for settling tube analysis is that the settling velocity of a particle is a more fundamental dynamic property than any geometrically defined measure of size (i.e., sieving, thin sections, image analysis) with reference to its behaviour in a hydrodynamic environment (Gillespie & Rendell, 1985). Because particle mobility in liquids (air, water) is dependent on the ratio between shear velocity and settling velocity (Francis, 1973), the settling velocity distribution and therefore the “sedimentation diameter” distribution is argued to be more valid for the characterization of sand texture than sieve-determined size distributions (Middleton, 1976; Bridge, 1981).