IDENTIFYING COASTAL SUBENVIRONMENTS OF BOGUE BANKS, NORTH CAROLINA USING FORAMINIFERAL ASSEMBLAGES AND GRAIN SIZE ANALYSIS

This study is part of an investigation to determine whether foraminiferal assemblages can be used to distinguish between coastal subenvironments in coastal North Carolina. Five previously sampled vibracores from off Bogue Banks, North Carolina were utilized to determine whether foraminiferal assemblages differed between ebb tide delta and inlet environments. These cores were relogged and sampled in new locations to improve the resolution of the Holocene section of each core. The samples were wet sieved over nested 710 and 63 micron sieves to remove mud and coarse grained material. The sand fraction was floated using sodium polytungstate to separate foraminifera from siliciclastic material. Approximately 100 specimens were picked at random and identified.

Holocene assemblages from inlet cores were dominated by rotaliids (50%-94%) with subsidiary miliolids (6%-48%). Textulariids were rare (<2%). Elphidium excavatum, Quinqueloculina seminula, Quinqueloculina lamarckiana, Ammonia tepida, and Ammonia parkinsoniana were the five most abundant species in the samples. Holocene assemblages from ebb tide delta cores were also dominated by rotaliids with miliolids being less abundant (1%-22%). Textulariids were rare (<1%). In the inlet cores, diversity (Fisher’s alpha) ranged from 2.215 to 2.698. The ebb tide delta samples exhibited Fisher’s alpha ranging from 3.017 to 6.166. Samples of Holocene sediments from both environments contained fossil foraminifera derived from offshore outcrops of Miocene strata. Inlet samples contained 13% to 63% fossil specimens whereas ebb tide delta samples contained 6% to 35% fossil specimens. These results support previous findings that the inlet and ebb tide delta environments can be distinguished by their foraminiferal assemblages, particularly by diversity and the relative abundance of miliolids.