HOLOCENE CONCRETIONS FROM THE NEW YORK BIGHT

The New York Bight is a shallow body of water that geographically sits between Long Island and New Jersey. Sedimentation in the Bight is attributed to differential erosion from coastal plain sediments along with sediments derived from the Pleistocene glaciation. Fossiliferous concretions deriving from these sediments are found washed up on New York and New Jersey beaches in the apex of the Bight. Concretion abundance decreases southward from Sandy Hook, NJ, and eastward from Rockaway Beach, along the south shore of Long Island. Fossils within concretions are of species presently living in Bight waters. Common fossil constituents in some concretions include estuarine species such as Crassostrea virginica, while others contain shoreface forms such as Anomia simplex and Mytilus edulis, thus indicating that concretions originally formed in different coastal environments. Study of concretion framework materials suggest that most are composed predominately of fine to coarse quartz grains. A small number are primarily carbonate. Thin section and SEM imagery are currently being done to strengthen observations on framework and matrix mineralogy, as well as microfossil content. XRF analyses indicate that in addition to Si, Fe, Sr, and Ca, many concretions show the presence of some rare earth elements (REE). Documented thus far are groupings of high abundance of like elements from Sandy Hook, NJ, and Riis Park (Queens, NY). Included in this grouping are the elements: Sr, Nd, Ba, Ce, and Pr. Concentrations of Ce, Pr, and Ba are particularly high from the eastern Riis Park concretions and those from Rockaway Beach (eastern Queens, NY). Geographically, concretions that are similar in elemental content are also relatively similar in physical characteristics such as color, matrix, and grain size. These observations suggest that there are probably multiple sources for concretions and that concretion occurrences on NY Bight beaches are produced by relatively stable or repetitive current patterns in the Bight apex.