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Biotical and sedimentological investigations were focused on the NW Black Sea, from the Danube Prodelta up to the abyssal zone. In the Danube Prodelta, terrigenous mainly non-carbonate muds (CaCO3<10%) dominate the Upper Holocene sedimentary processes. From the southern part of the Danube Prodelta, the sediments yielded several rhythmic sequences of clayey silts and silty clays. Reworked nannofloras from older Cretaceous, Paleogene and Neogene deposits were observed.
To the southern part of the Danube Prodelta, the Upper Holocene sediments are mainly represented by sands and sandy clays. The sands contain unbroken shelly material to shelly detritus and variable amounts of clay matrix. Mixed brackish and marine taxa were observed in the core sediments. Below 40 m water depth, the cores contain the bloom of the Emiliana huxleyi nannoplankton species, together with frequent taxa of the calcareous dinoflagellate genus Thoracosphaera. The next interval yielded foraminiferal assemblages with Porosononion tuberculatum, Elphidiella sp., Elphidium ponticum, Ammonia beccarii, and Ammonia viennensis. The Upper Holocene bottom sediments of the NW Continental Slope of the Black Sea are overlaid by a semiliquid "fluff" layer, 3.5-4.5 cm thick, enriched in organic matter. Continuous accumulation of fine laminated carbonate coccolith oozes, organic matter rich, took place in the above-mentioned area. These sediments contain the acme of the calcareous nannoplankton species Emiliana huxleyi. Reworked nannofossils from older Cretaceous, Paleogene and Neogene deposits, making around 20% of the total nannofloras, are present. The bottom part of Upper Holocene section (60 cm deep) is represented by a thin 1-4 cm layer of coccolithic ooze, accumulated during the first appearance of Emiliana huxleyi in the Black Sea. A thin transition layer of sapropelic mud (2-3 cm) marks the short period of its disappearance. Then, the main layer of coccolith ooze continue upwards in the section. Below the acme of Emiliana huxleyi, an interval containing nannofloral monospecific assemblages with Braarudosphaera bigelowi was identified. Sapropelic fine laminated muds and sapropels characterized the Middle Holocene sedimentation.
In the abyssal area of the NW Black Sea, Upper Holocene fine laminated carbonate coccolith oozes, enriched in organic matter, accumulated. Sapropelic muds and sapropels mainly characterized the Middle Holocene sedimentation. Similar nannofloral features as described above from the continental slope were recorded in the abyssal regions.
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