Late Holocene microfaunal and nannofloral assemblages of the NW Black Sea

Abstract. This study describes the fluctuation pattern in Late Holocene microfaunal (i.e. foraminifera and ostracods) and nannofloral assemblages of two cores collected from the Romanian Black Sea shelf, at a water depth of 28 and 66 m, respectively. The lithology of the cores is mainly characterised by blackish muds, alternating with thin, centimetres-thick sand and coquina layers. The microfaunas are dominated by brackish foraminiferal and ostracod assemblages that are still common in the actual Black Sea communities, living nowadays at water salinity lower than 18 ‰. In the shallower water Site EF 08-01, the abundance ratio between Caspian and Mediterranean ostracods is 0.7, while in the deeper water Site BS 08-055, the abundance ratio between Caspian and Mediterranean ostracods is 0.01. These data argue for the dominance of Mediterranean ostracod fauna with lower abundance in shallower environments of the Black Sea and with a very high abundance in the deeper parts of the internal shelf, i.e., at a water depth of 66 m. Based on the calcareous nannoplankton fluctuation, four Nannofloral Intervals were identified, which indicate a gradual salinity increase of the surface waters during the deposition of the Late Holocene Shallow Unit. In the same interval, the benthic microfaunas (ostracods and foraminifers) argue for a more stable salinity environment in the two studied cores from the Black Sea inner shelf