Paper No. 208-16
Presentation Time: 9:00 AM-6:30 PM
A COMPARATIVE SEDIMENTOLOGICAL INVESTIGATION INVOLVING BEACH SAND DEPOSITS: FAR ROCKAWAY (QUEENS) AND MONTAUK POINT (LONG ISLAND), NEW YORK
This sedimentological study is focused primarily on the beach sand deposits in Far Rockaway, Queens, New York City, and Montauk Point, Long Island, New York. Primary research objectives were to compare and contrast between the beach sand deposits including grain-size distribution, grain shape characteristics, detrital mineral composition, heavy mineral assemblages, and immobile trace element data. 50 representative samples from Montauk Point and Far Rockaway provided the basis for conducting grain size and compositional investigations and were collected during the low tide regime for extensive aerial coverage. While collecting samples, emphasis was given to isolated beach placer deposits often displaying purple coarse-grained sands rich in garnet and magnetite. These were considered to be lag deposits due to selective segregation of denser minerals and winnowing of lighter minerals. Magnetite grains were separated by using hand magnets and studied under the polarizing microscope for deciphering weathering index and grain shape. To assess how much of an effect weather and shoreline process have on the sand in a particular location, results obtained from grain size and compositional data were utilized. Differences in grain size, sorting, roundness, compositional (both light and heavy minerals), immobile traces and magnetite concentration were noted between the Far Rockaway and Montauk Point sand deposits. Overall, Montauk Point sands were coarser, moderately sorted, rich in magnetite (15 to 22%) and garnet, and negatively skewed; whereas, Far Rockaway sands are fine-grained, well-sorted, have abundant quartz and a trace amount of magnetite (less than 1%). Among the other notable heavy minerals, Montauk sands revealed a greater proportion of zircon, tourmaline, ilmenite, and rutile. Trace element distribution also reflects an anomalous behavior between the two deposits: Montauk sand recorded significantly higher concentration of Ce, Ti, Zr, and Cr. These can be attributed to the variable shoreline activities, hydraulic sorting, nature of coastline, and original composition of the glacial deposits from which the beach sand is derived.