Influence of Fluids on the Species Composition and Preservation of Microfossils in Biogenic Carbonate Sediments in the Pobeda Hydrothermal Cluster (Mid-Atlantic Ridge)

Based on materials obtained during Cruise 37 of the R/V Professor Logatchev in the Russian exploration area, the species composition, distribution, and preservation of nanno- and microfossil carbonate shells in biogenic bottom sediments within the Pobeda hydrothermal cluster (17°07.45′–17°08.7′ N MAR) were studied. Physicochemical parameters and total carbonate content were measured and their changes along column sections were revealed. Based on the coccolith assemblages, the studied sediments are assigned to the upper part (acme) of the biostratigraphic zone Emiliania huxleyi. It has been established that the hydrothermal activity zone (Pobeda hydrothermal cluster) is marked usually by a decrease of both total population and species diversity of microrganisms in the lower part of columns. The column is also marked by downsection decrease of Eh, pH, and carbonate content. These changes are attributed to the influence of diffuse hydrothermal fluids.