Environmental changes in the declining Middle Miocene Badenian evaporite basin of the Ukrainian Carpathian Foredeep (Kudryntsi section)

Environmental changes in the declining Middle Miocene Badenian evaporite basin of the Ukrainian Carpathian Foredeep (Kudryntsi section) The Kudryntsi section in West Ukraine documents a major environmental change from hypersaline to marine conditions during the Middle Miocene. There are very few (or no) specimens of foraminifers in samples of the siliciclastic series (4 m thick, with limestone intercalations) which occurs above the gypsum (and below the transgressive deposits) in the southern part of quarry. The limestone intercalations are first sparitic and microsparitic, and then become pelletal. The pelletal depositional textures are interpreted as originated in restricted environments in contrast to mixed-fossil lithoclastic packstones/grainstones overlying the siliciclastic series. The diversity of fauna increases up section. Foraminifers, bivalves, ostracods and gastropods appear first and then, additionally, brachiopods, bryozoans, crinoids, and echinoids occur. Foraminiferal assemblages are dominated by elphidiids forming 70 to 90 % of the population. The most common species are Elphidium crispum (Linné) and E. macellum (Fichtel & Moll). The limestones show a wide range of δ13C values (from -1.6 ‰ to - 18.2 ‰) and δ18O values (from -0.2 ‰ to -9.4 ‰) indicating that the cementation and some recrystallization took place in meteoric-water-dominated fluid but the restriction-controlled trend can be recognized. The siliciclastic series was deposited in an evaporitic lagoon influenced by large inflows of continental waters carrying the siliciclastic and other detrital material from the older Badenian rocks as well as from their substrate. The Kudryntsi section documents a stepwise decrease in water salinity — from ca. 150-300 ‰ during the Badenian gypsum precipitation, through ca. 80-150 ‰ during deposition of the siliciclastic series to ca. 35 ‰ during sedimentation of the basal transgressive deposits. The basal deposits originated in shallow subtidal (0-20 m) environments of normal marine salinity (30-35 ‰) and temperate to warm waters (8-18 °C) as indicated by requirements of the E. crispum association in recent seas.