The source of sand for the Killpecker sand-dune field,southwestern Wyoming

The primary source of sand for the Killpecker sand-dune field is the Laney Member of the Green River Formation (Eocene) and not the glaciofluviatile deposits to the west as previously believed. This contention is based on data from heavy-mineral analyses, grainsize parameters and outcrop locations of possible sand sources. The heavy-mineral assemblage of the dune field includes in order of decreasing frequency epidote, greenbrown hornblende, blue-green hornblende, magnetite, garnet, zircon and a variety of other heavy minerals in minor amounts. Earlier studies based on moment measures from sieved sands indicated that textural parameters such as positive skewness define the eolian environment. Textural parameters in this study were determined by graphic measures from settling-tube curves which had been calibrated both for glass beads and sieved natural sand. The use of textural parameters such as positive skewness to define eolian environments is not supported by the data of this study. Skewness was found to be linearly dependent on mean grain size with a critical value of $\text{?1.7 φ}$ (0.31 mm) separating positively and negatively skewed samples. Sand coarser than 1.7 φ (smaller or negative φ) was positively skewed and sand finer than 1.7 φ was negatively skewed.