A COMPARISON OF BEACH AND DUNE SANDS ALONG THE SOUTHERN OREGON COAST, USA

Twenty-five samples were collected along the southern Oregon coast from Florence to the Oregon/California boarder in an attempt to determine differences between beach (ORB) and adjacent dune (ORD) sands. Samples were sieved (to half phi size) and statistics were calculated with GRADISTAT. XRD analysis and thin sections were prepared from each sample.

Beach sands ranged from coarse to fine sand (0.140-2.172 Ø) with only one of 13 samples being fine sand. Dunes ranged from medium to fine sands (1.141-2.565 Ø). Beaches ranged from poorly sorted to very well-sorted (1.062-0.302 σ) with only one poorly sorted and one very well-sorted sample. Dunes ranged from moderately well-sorted to very well-sorted (0.549-0.308 σ), with only one moderately well-sorted sample. Folk and Ward’s (1957) definitions were used for grain sizes and sorting values.

For beaches, rounding of quartz and K-feldspar ranged from 1.5-3.5 and 2.5-4, respectively. For dunes, it ranged from 2.5-3.5 and 3-4.5, respectively. Rounding definitions of Folk (1955) were used, 0.0 being the most angular possible and 6.0 being the most rounded possible. From beach to dune, percentages of quartz increased slightly and percentages of K-feldspar and plagioclase decreased slightly.

Beach sands tend to be coarser, more poorly sorted, less rounded and quartz poor compared to dune sands that tend to be finer, better sorted, more rounded and quartz rich. The assumption is that beach sand is winnowed to produce adjacent dune sands. When comparing the average quartz grain size in dune sands to the same sized sand grains in beach sands, the rounding is about the same, indicating very little rounding took place during eolian transport of the sand. Heavy minerals show a marked decline in the dune sands, indicating selective winnowing of quartz during the eolian transport process. K-feldspar, about the same density as quartz, is less abundant in the dune sands, but much better rounded, indicating probable mechanical abrasion of this mineral during eolian transport. We thank Calgary Rock and Materials Services Inc. for funding and laboratory work.