Biostratigraphy of the Konkian (Middle Miocene of the Eastern Paratethys) deposits of Southern Ukraine based on foraminifera

摘要

The Konkian (Middle Miocene) foraminiferal assemblages and molluscs from five Wells situated in Southern Ukraine were studied in order to correlate the palaeoecology and biostratigraphy of the coeval palaeobasins with different environmental conditions. The article contains comprehensive analysis of controversial issues of the Konkian stratigraphy of the Eastern Paratethys and additional keys for determination of Konkian development phases by foraminifera and molluscs. Five stenohaline normal-marine, two euryhaline and one mixed foraminiferal assemblage were identified in different levels in the investigated wells with the analysis of their accordance to different molluscs assemblages. The study defines an isochronous foraminiferal assemblage for some wells, suggests a palaeoecological and stratigraphic reconstuction of the middle Miocene sediments in the Eastern Black Sea Region and recognizes two models of development of the Konkian foraminiferal assemblages. These models show the differences between environmental conditions in the shallow-water basin of the Eastern Black Sea Region and deeper water basin of the Kerch Peninsula at that time. While the Eastern Black Sea Region was influenced by frequent and abrupt changes in environmental conditions during almost all Konkian time, a relatively deeper basin of the Kerch Peninsula had a successive phase. The late Konkian time created similar depositional conditions for both basins.