BEACH MORPHOLOGY AND CONSTRAINTS ON HEAVY MINERAL SEGREGATION: THE CRESCENT BEACH , SOUTH PORTLAND, MAINE

The Crescent Beach (43°33’24”N, 70°13’27.06”W) provided an ideal location for conducting mineralogical investigation of shoreline sediments, since bulk of the shoreline sediments are considered to be pristine and not being negatively impacted by any recent developments. Representative beach sand samples were investigated for obtaining median grain size, average sorting, light, and heavy mineral data. Sand samples were taken from three points on the beach: eastern, western and mid-point. The eastern-most samples are generally skewed towards finer grains than the mid-point or western. The western samples are skewed towards coarser grains and increase in coarseness from low to high tide. Mid-point samples are generally not skewed and are better sorted than either the eastern or western samples. Sodium Polytungstate (density of 2.9 g/cc) was used for heavy mineral separation and results show a higher concentration of denser material at the mid-point than the two outer locations. Careful investigations of the morphology of the mid-point locations, revealed non-linear landscape compared with the eastern and western areas. Presence of localized irregular landscape perhaps caused refraction of waves and it is hypothesized that the mid-point of the beach is more acted upon by the waves and, therefore, the less dense material is removed. Preliminary petrographic analysis reveals garnet as the dominant mineral, with zircon, tourmaline, staurolite, epidote and green hornblende, all of which display noticeable textural, weathering/alteration, and compositional characteristics under microscopic analysis. Garnet exhibited a wide range in terms of compositional and textural anomaly, followed by tourmaline, and hornblende. The composition of the samples suggests a heterogeneous provenance comprised mostly of felsic to intermediate igneous and medium to high-grade metamorphic rocks with subordinate contribution from reworked sedimentary rock. Segregation of heavy minerals within the various sand sizes indicates hydraulic sorting and nature of coastline and presence of localized non-uniform beach morphology, largely influenced the distribution of heavy minerals within the sand fraction.

Funded by US Dept. of Education (USDOE) Grant titled "Enhancing African American Students' Talents."