FORAMINIFERAL ASSEMBLAGES OF THE SHOREFACE AND INNER SHELF OFF BOGUE BANKS, NORTH CAROLINA

Four vibracores were selected to determine whether Holocene shoreface and inner shelf sediments off Bogue Banks, North Carolina can be distinguished by their benthic foraminiferal assemblages. Sample locations within the four cores were determined to complement a previous foraminiferal study. From these cores, nine samples were soaked in a dilute sodium hydroxide and sodium hexametaphosphate solution to disaggregate the sediment. The samples were wet sieved over a nest of 63 μ and 710 μ sieves to remove mud and coarser sediment. The resulting sand fractions were floated using the heavy liquid sodium polytungstate to concentrate specimens of foraminifera. Approximately 100 specimens were picked at random from the float and identified, if possible, to the species level.

Results indicate slight differences in foraminiferal assemblages for the shoreface and inner shelf cores. The foraminifera are mostly Holocene (56-100%), but up to 7% of shoreface assemblages and 13% of inner shelf assemblages consist of reworked Miocene fossils. Holocene shoreface assemblages contain 86% to 90% Rotaliina, 14% to 31% Miliolina, and 0% Textulariina. In contrast, Holocene inner shelf assemblages have 69% to 100% Rotaliina, 0% to 31% Miliolina, and 0% Textulariina. Within the shoreface samples, Ammonia parkinsoniana, Ammonia tepida, Elphidium mexicanum, and miliolids are more abundant than within inner shelf samples. Planktonic foraminifera are rare. In the shoreface, species diversity (Fisher’s alpha) increases up-core, ranging from 8.238 to 17.442. The results of this study indicate that shoreface and inner shelf environments are not easily distinguished by their sedimentological characteristics. However, there are slight differences in foraminiferal assemblages between the two environments.