Sedimentology of the Beach Placer Deposit, Montauk Point, Long Island

Garnet and magnetite rich sand, also enriched in monazite and zircon, has been observed and sampled near Montauk Point, Long Island. Hydraulic segregation of these components, by wave action, is responsible for producing a placer deposit of heavy mineral-rich sand. The loosely consolidated material is directly exposed to ocean waves, thus acting as a sediment source for longshore transport of sand sized sediment in a westward direction along the southern shore. Groins, built on the south shore of the island, trap the sand from the longshore transport to protect the beaches in the east but cause depletion of sand for the beaches at the western end of the island. This sediment was analyzed for its relative abundance of certain trace elements and it was shown to share similar concentrations of the same elements in the till and stratified drift of the Ronkonkoma Moraine. However, although the placer beach deposits are closer in proximity to the Ronkonkoma Moraine, further chemical analysis indicates some similarities between the trace element compositions of the placer deposits and the stratified drift of the Harbor Hill Moraine. It is believed that sand transported along the coast comes from erosion of the bluffs at Montauk, but studies of the composition and erosion rates of these bluffs indicate that their erosion alone is insufficient to account for the entire volume of sand. It is possible that some originates from the erosion of the mainland and barrier beaches, and perhaps from offshore deposits, as well. Finally, beach replenishment may have taken place, where sand is placed on the shore to build up the beach. The relative contribution of these sources is not yet clearly identified.

** Current research was supported by a LSAMP (The New York City Louis Stokes Alliance For Minority Participation) scholarship awarded to Andrew Singh