LATERAL FRACTIONATION OF LIGHT AND HEAVY MINERALS: ROBERT MOSES STATE PARK, LONG ISLAND, NEW YORK

Preliminary sedimentological investigations involving grain size distribution, grain shape, mineral composition, and trace element concentrations associated with recent beach sand collected from Robert Moses State Park, Long Island, New York were carried out on several representative samples to characterize the sand and highlight depositional environments. Robert Moses State Park is located on the western end of Fire Island, outside of the boundaries of Fire Island National Seashore. Geologically, Robert State Moses Park is part of greater Fire Island coastal province. Fire Island is a narrow barrier island protecting the south central coast of Long Island from Atlantic storms. The barrier island stretches for 32 miles, bounded by Moriches Inlet to the east, and Fire Island Inlet to the west. Nowhere is the island wider than a mile. At some locations along its eastern and central portions the width can be as little as several hundred yards (USGS, 2014). Most of the analyzed sand samples displayed coarse to medium-grained and well-sorted population with dominance of well-rounded quartz particles. Apparently there is evidence of lateral fractionation of heavy minerals and shell materials due to longshore transport since most of the samples located distally are enriched in fragmented shell components and subrounded to angular detrital quartz grains. Furthermore, proportion of total magnetic concentration with respect to certain sand sizes (US Standard Sieve Mesh: 60 to 230) also exhibited this phenomenon by having diminishing content with respect to distal location. Representative trace element data in conjunction with detrital and accessory mineralogy reflect an overall greater concentration of stable traces including Zr, Ti, quartz, zircon, tourmaline, garnet, and rutile; however segregation of these components were constrained by the local bathymetry and topographic features. Super storm Hurricane Sandy also played a key role in obliterating and reshaping the coastal landscape and locally exerting new constraint on beach sand composition and establishing final mineralogy. Detailed chemical analysis coupled with heavy mineral separation can shed more light on the nature of beach sand deposition in Robert Moses State Park.