Stratigraphy of the Pliocene deposits of the Black Sea (Ukraine) according to evidence from ostracods (Arthropoda, Crustacea)

Abstract

This article presents a detailed analysis of the taxonomic composition of the Pliocene (Kimmerian, Kujalnikian) and Eopleistocene (Gurian) ostracods in the northern part of the Black Sea. It presents the patterns of the stratigraphic position of the fossil ostracods in the Miocene - Quaternary and their geographic distribution in Western and Eastern Europe (the Pannonian Basin, the Dacian Basin, the Euxinian basin of the Paratethys) and the Mediterranean region.Wedetermined the characteristic species for the Kimmerian, Kujalnikian and Gurian in the northern part of the Black Sea. We established a change in the taxonomic composition of ostracods at the Pliocene (Kujalnikian)/Eopleistocene (Gurian) boundary, namely the disappearance of a large number of Pliocene species and the appearance of new species. Ten species disappeared in the Kujalnikian Cyprideis pontica, Euxinocythere (M.) crebra, Amnicythere mironovi, Camptocypria lobata, Loxoconcha subcrassula, Loxoconcha verticalitercostata, Xestoleberis (X.) cellulocus, Xestoleberis (P.) communis, Candona (C.) expressa, Ilyocypris caspiensis; one species Amnicythere postbissinuata appeared in the Gurian. The brackish water species Cyprideis pontica is the Kujalnikian index species. The stratigraphic position of Cyprideis pontica in the Mediterranean Basin, Pannonian Basin, Dacian Basin, Euxinian Basin (Black Sea) in the Miocene-Quaternary is analyzed. The time of the disappearance of Cyprideis pontica in the Mediterranean, Pannonian and Dacian basins (Messinian, Pontian/Zanclean, Dacian, Kimmerian boundary) and in the Black Sea (Kujalnikian/Gurian boundary) is established. The diagnostic morphological features of the shell Cyprideis pontica (morphology of the surface pore canals) are established and described, which allows us to place this species in the Neogene deposits. Surface pore canals are different shape, sievetyped, deepened in relation to the surface of the valve. Sieve-shaped lamella contains 110-270 internal pores. The internal pores have a staggered shape, the diameter of the osculum of the internal pore is 302-994 nm; diameter of the central pore is 977 nm-1.8 μm). The evolution of Cyprideis pontica, which was separated from the parent species Cyprideis torosa in the Late Miocene, was reconstructed. In the occupation of a new ecological niche with a reduced oxygen content in deeper water biotopes, in the process of adapting to the conditions of hypoxia and necessity of increasing the volume of water filtration, there was a restructuring of the morphology of the surface pore canals of the shell Cyprideis torosa. This involved an increase in the size of the sieve-shaped lamella, the number of internal pores in the sieve-shaped lamella and the size of the osculum of the inner pore. A new morphotype Cyprideis pontica was thus formed within the existing Parathetys-Mediterranean basins. It had a mosaic, ecologically isolated range that coincided geographically or overlapped with the range of the species Cyprideis torosa (sympatric evolutionary speciation). The range of Cyprideis pontica and the dynamics of its populations in the Euxinian Basin during the Sarmatian-Kujalnikian have been reconstructed.