The dissertation devoted to reconstructing the Late Pleistocene - Holocene sedimentary conditions and palaeoenvironments in different parts of the Black Sea based on the results of diatom analysis. On silicious micropalaeontological data the direction of changes of sedimentological conditions near the Ukrainian shores were revealed. The vertical trend of relative abundance of diatom ecological groups at the sedimentary sections in the North-Western Black Sea shelf indicates the successive environmental transformations under the influence of abiotic agents. This region was characterized by shallow water, littoral/sublittoral conditions, and salinity fluctuations in the Holocene. The diatom technique allowed to reconstruct the Late Pleistocene-Holocene sedimentary environments in shallow coastal part of the Karkinitskyi bay. In the Upper Pleistocene horizons was formed the freshwater diatom assemblage with the dominance of freshwater and brackish-freshwater epiphytes Epithemia turgida, E. adnata, E. sorex, Cocconeis placentula, Rhopalodia gibba. Epiphytic are characteristic of shallow low-dynamic environments with low range of salinity. In the Early Holocene freshwater estuarine conditions were changed to irregularly flooding. The lowest part of the Lower Holocene sediments contains diatom assemblage with mixture of brackish to freshwater epiphytes, epipelon, and aerophilous Anomoeoneis sphaerophora, Pinnularia viridis, E. turgida, E. adnata. The rise of the sea level and salinity brought to occurrence of shallow brackish lagoon in Early-Middle Holocene with appearance of 'campylodiscus' assemblages. The assemblages of upper part of the Lower Holocene and Middle Holocene muds are characterized by disappearance of freshwater species and appearance marine ones in planktonic group. Most abundant is marine-brackish epipelon. The diversity of the taxonomic composition is low; dominant taxa are Campylodiscus echeneis, C. daemelianus, C. clypeus. Such ecological group is characteristic of shallow lagoons and estuaries with salinity range of 5-17 ‰. A typical oceanic littoral species Terpsinoe americana was found in the Lower-Middle Holocene sediments. It is the first occurrence of T. americana in the Black Sea Quaternary. There are conditions of marine littoral in the Late Holocene. In Upper Holocene muds was formed the assemblages with prevalence of allochthonous marine planktonic taxa Actinocyclus octonarius, Paralia sulcata. This group is formed in low-tidal littoral environments with water salinity of 15-17 ‰. The gradual replacement of freshwater-brackish diatom species to marine ones, the increasing of number and abundance of marine taxa, from bottom to top, and predominance of marine plankton in upper part of sections are the evidence of Holocene sea-level and salinity rising. Together with the strong fragmentation of the valves, this all points to hydrological regime activation. The Early-Middle Holocene diatom flora in the coastal part of the Karkinitskyi bay with the dominance of Campylodiscus, Surirella, Diploneis, Tryblionella genera in the benthos, and Paralia, Actinocyclus, Thalassiosira ones in the plankton are characteristic of relatively closed of the sea shallow brackish lagoons. Such assemblages are known in similar interglacial (the Northern Sea, the Far East) and postglacial (the Baltic Sea) deposits. The Middle Holocene Littorina Sea transgression in the Baltic Sea was identified according to increased number of brackish diatoms, such as C. clypeus, C. echeneis, T. americana. Mentioned species are an indication of water salinity increase in the Baltic Sea during Atlantic climatic optimum. Specific brackish diatoms can be used as an evidence of Middle Holocene climatic optimum in the Black Sea as well as in the Baltic Sea. We suppose that according to specific diatoms it is possible to trace Middle Holocene climatic optimum not only in the Baltic Sea but in the Black Sea also. A participation of a sediment re-deposition in a forming of the Upper Pleistocene-Holocene bottom deposits in different parts of the Black Sea was determined. On the basis of taxonomic composition and ecological structure of the Black Sea Late Pleistocene-Holocene diatom complexes with the Miocene-Pleistocene microalgae elements the sources and ways of sedimentary matter were defined. New monitoring data on siliceous microalgae assemblages in the Black Sea Experimental Polygon near the South Crimea shore are examined. Seasonal changes on diatom number and abundance are analyzed. Perspective applications of diatom technique for the monitoring of abiotic influence on sedimentary processes are proposed.
