SEDIMENTOLOGY AND FAUNAL CHARACTERISTICS OF RARITAN BAY BEACHES

Raritan Bay is a major estuary of the New York Bight. It receives sediment from the waters of the Bight, as well as from the Raritan and Hudson Rivers. We sampled sediment and wrackline shell debris at beach localities on the south shore of the Bay as a means of quantifying sediment and animal distributions in littoral bay environments. Samples were sieved using standard phi scale sieves, heavy minerals were extracted using sodium polytungstenate solutions, and grain composition was determined by microscopic analysis. Beach sediments become coarser and more poorly sorted from Sandy Hook westward toward the head of the Bay. Grains are rounded and spherical at Sandy Hook and become more discoidal toward the Bay head. Monomineralic quartz grains dominate all samples. Glauconite is the main dark component with magnetite, ilmenite, and garnet of lesser abundance. The wrackline assemblage at Sandy Hook is dominated by surf clams (Spisula), blue mussels (Mytilus), and lady crabs (Ovalipes). Faunal assemblages in the Bay interior are dominated by slipper shells (Crepidula), ribbed mussels (Geukensia), and jackknife clams (Ensis). Sites in the Raritan River upstream of tidal flux are dominated by the northern pearl mussel (Margaritifera). Except for the venerid clam (Corbicula), which is found at all sites, most species occur at a single site or at adjacent sites. We interpret these results to indicate that sediment abrasion and transport is more effective on ocean facing beaches in removing soft and more easily transported grains. Some sites show that grain size distribution depends also on man-made structures which influence flow. Glauconite derives from Cretaceous sediments, especially the Navesink Formation, which outcrop along the shoreline near the eastern sample sites. Heavy mineral composition reflects glacial transport of granitic and gneissic rocks from northern New Jersey and New York. Species diversity decreases westward in Raritan Bay and appears to be related to changes in such factors as salinity and sediment type.