CHARACTERIZATION OF LITTORAL SANDS FROM OWEN BEACH IN TACOMA, WASHINGTON STATE

Owen Beach is located in Point Defiance Park in Tacoma, Washington on the south Puget Sound. It faces northeast, and is effected by wind waves, and mixed tidal current. It is a mixed sand and gravel beach derived primarily from Pleistocene glacial and interglacial sand and gravel cliffs near the shore. The composition, sorting and microtextures of the beach sands were studied. Relative percentages of quartz, feldspar, and rock-fragments were determined by hand sorting under a binocular microscope and plotted on a QRF triangle. Two samples from Point Defiance were sieved and Folk and Ward (1957) equations were used to determine modal class, median and mean phi, sorting skewness and kurtosis. Quartz grains were mounted for secondary electron imaging with a scanning electron microscope. SEM images were gathered and compared with historic and recent literature on the subject. A subsample of sand was made into an epoxy block and polished to measure composition of some of the grains with SEM microbeam analysis. The sands are composed primarily of quartz, feldspar (mainly plagioclases), rock fragments, composite grains and minor amounts of pyroxenes, amphiboles, garnet, and iron – titanium oxides. It is identified as a lithic sand with medium mean phi size, medium sorting, and negative skewness. Microtextural analysis showed that the sands were more representative of their glacial-fluvial source than their current littoral environment. For comparison, the same analyses were done on the sand from the Nisqually River at Elbe in Washington State. Similarities between the Nisqually sediments and Owen sands might be explained by the short time that the Owen Beach sediments have spent in their current littoral environment.