Остракоди крайових частин Борисфенської затоки Східного Паратетису в середньому сарматі

Abstract

This work continues the analysis of assemblages of ostracoda from the Middle Sarmatian deposits of the Borisphen Gulf of the Eastern Paratethys. Ivanova at al. (2007), Bondar (2015) present data on the history of the study of Sarmatian ostracods, on the factual data, methods of study, and lithological and palaeontological description of the composite Sarmatian sections of the marginal parts of the Borisphen Gulf. This publication presents a palaeoecological analysis of the ostracod assemblages, which contributes to the description of the shallow-marine environment which existed in the Middle Sarmatian basin. The material studied consists mainly of benthic ostracods, closely associated with the near-bottom environment of the basin. This makes them a reliable indicator of the palaeoecological environment. Any changes of the living environment is leaded to restructuring of the entire ostracod assemblage. The main environmental factors, influencing the systematic and quantitative composition, and the domination of one taxa over others, include water depth, salinity, hydrodynamic conditions in the basin, temperature conditions, substrate type, and organic carbonate and oxygen content of the water. The reconstruction of the palaeoenvironment is based primarily on the actualistic approach, where the environmental parameters of modem communities are extrapolated to the ancient fauna with certain assumptions. A total of 16 species of ostracod, belonging to 6 genera of 6 families, were identified in the Middle Sarmatian deposits. Investigation of these ostracod assemblages included taxonomic, quantitative, taphonomic and palaeoecological analyses. The palaeoecological analysis of ostracods from the deposits of the marginal parts Middle Sarmatian sea demonstrates that the assemblages developed in the more or less favorable environments of a warm shallow basin (deep up to 20 m, temperature about 20 oC). Limited diversity of the species, abundance of certain specimens, large and heavy shells of ostracods are typical of the shallowest parts of a basin with active hydrodynamic environments (Aurila). The highest taxonomic diversity of the ostracod associations was encountered in the fairly shallow and calm environments with low sorting of substrate and weak near-bottom hydrodynamics (Loxoconcha, Leptocythere). The salinity of the basin was unstable. So there are Cyprideis torosa, Cyprinotus luminosus in the assemblages.