HURRICANE-DRIVEN SEDIMENT TRANSPORT ON BEAR ISLAND AND BEAR INLET, NORTH CAROLINA, BASED ON FORAMINIFERAL AND SEDIMENTOLOGIC EVIDENCE

This study is part of a continuing multiyear investigation (sampling in 2016, 2018, 2019 and 2023) to trace sediment transport from offshore during hurricanes using foraminiferal and sedimentological characteristics within different environments on Bear Island, North Carolina. 2016 data were collected after several years of hurricane quiescence, 2018 and 2019 data were collected immediately after hurricanes Florence and Dorian, respectively, and the 2023 data were collected after four years of quiescence.

2023 sediment samples show a mean phi range of 2.58 to 1.42 phi (fine to medium sand), a sorting range of 0.76 to 0.32 phi, and a skewness range of -1.15 to 0.52 phi. Coarsest sediments occur in the longshore trough (LST) whereas the finest sediments occur in the dunes (D). Moderately sorted sediments occur in the LST, and well sorted sediments occur in the dunes. These findings are consistent with those of previous years. 2023 foraminiferal data show that most specimens, as in previous years, are modern (range 35%-79%); the most abundant species were Elphidium excavatum, Ammonia parkinsoniana, Quinqueloculina seminula, Quinqueloculina lamarckiana, and Hanzawaia strattoni. All 2023 samples, as in previous years, contain fossil foraminifera transported onshore from seabed outcrops of Miocene strata, presumably by severe storms. Upper foreshore, proximal and distal washover samples contain most fossils (46 to 65%) in 2023; 15%-62% of fossils were phosphatic and 37%-84% were “sugary” in appearance due to crystal overgrowths.

Although the percentage fossil foraminifera range considerably in various subenvironments and from year to year, fossil foraminifera are more abundant immediately following hurricanes (48.5%) compared to 38.7% after several years of hurricane quiescence. Phosphatic fossils were more abundant following Hurricane Florence (2018) whereas sugary fossils were more abundant following Hurricane Dorian (2019) suggesting different sources of sediment on the adjacent shelf. Preliminary results, therefore, suggest foraminifera can be used to trace sediment transport pathways during strong storms over the shelf.