J. Richard Jones

Comparison between sieving and settling-tube determinations of sand sizes by using discriminant analysis

There is much controversy regarding the method that best measures the representative grain sizes used to calculate sediment statistics. Twenty-five sand-sized sediment samples were collected in barrier-island subenvironments and analyzed by a sieving technique and a settling-tube technique. On the basis of graphic sediment statistics as variables, discriminant analysis indicates that the more conventional sieving method correctly characterized 96 percent of the samples by subenvironments, while the settling-tube technique correctly characterized only 72 percent of the samples.

Preparation of Unconsolidated Sands for Microscopy Laboratory Exercises.

Microscopic examination of unconsolidated sands and coarse silts usually receives minimal attention in various sedimentology courses because of the difficulty of preparing adequate slides for study. Our technique for overcoming part of this problem is to impregnate small amounts of sandy sediment with a quick-curing resin. Once the sediment- resin plug is removed from a mold, it can be polished quickly for standard low magnification binocular (reflected light) microscopic studies. Using these easily made preparations, laboratory exercises with unconsolidated sands can be conducted efficiently for the determination of mineral composition, provenance, and grain roundness and sphericity in a manner that is comparable to the study of indurated sandstones in thin sections.