STORM AND SEA LEVEL RECORDS IN BASIN BAYOU, FLORIDA BASED ON FORAMINIFERAL ASSEMBLAGES FROM AN 8 KYR RECORD

Sediment cores from Basin Bayou, located on the northeast side of Choctawhatchee Bay in northwest Florida, record significant changes in the geomorphology of Basin Bayou over the mid-late Holocene. The area evolved from a freshwater river delta to a brackish estuary environment due to progressive marine inundation as a result of early Holocene sea-level transgression. By approximately 2 ka, a baymouth bar separated the bayou from Choctawhatchee Bay except when waves and surge inundation overtopped the barrier during tropical cyclone events. This study focuses on foraminiferal analysis of Core 4 collected from the center of the Bayou. Benthic foraminifera assemblages are useful for reconstructing past sea level since different foraminifera species thrive in different coastal habitats, salinity regimes and water depths. Foraminifera can also provide insight into the frequency of past hurricane events since storm-surge flooding can transport species living offshore in deeper water with higher salinity into fresher and shallower environments, such as coastal embayments. A total of 72 samples were taken at 10-cm intervals from the 8 kyr-long sediment core and analyzed for foraminifera species abundances. From 0-1.2m (present to around 2 ka), agglutinated foraminifera were abundant and included species typical of estuary and salt marsh facies such as Jadammina macrescens, Ammobaculites spp, Haplophragmoides spp, Miliammina fusca, and Ammoastuta inepta. Some foraminifera have been pyritized, indicating anoxia in sediment in some intervals suggesting intervals of higher organic content within the sediment and increased respiration in sediment pore spaces. Prior to 1.2m (2 ka), foraminifera were rare-to-absent, and those present are pyritized. There is a brief interval, 3.6-3.8m (4-4.5ka), when foraminifera, mostly pyritized, became abundant. we will present a more detailed analysis of foraminifera assemblages and provide further insight into the hurricane and sea-level records at Basin Bayou.