1. From Khersonian drying to Pontian 'flooding': late Miocene stratigraphy and palaeoenvironmental evolution of the Dacian Basin (Eastern Paratethys)
- Author
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Lazarev, S., de Leeuw, A., Stoica, M., Mandic, O., van Baak, C. G.C., Vasiliev, I., Krijgsman, W., Paleomagnetism, Institut des Sciences de la Terre (ISTerre), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Gustave Eiffel-Université Grenoble Alpes (UGA), and Paleomagnetism
- Subjects
Khersonian ,010504 meteorology & atmospheric sciences ,02 engineering and technology ,Late Miocene ,Oceanography ,01 natural sciences ,Sedimentary depositional environment ,Foraminifera ,Paleontology ,0202 electrical engineering, electronic engineering, information engineering ,Sedimentology ,Dacian basin ,Maeotian ,0105 earth and related environmental sciences ,Global and Planetary Change ,Invertebrate fauna ,biology ,020206 networking & telecommunications ,biology.organism_classification ,Polyhaline ,[SDU]Sciences of the Universe [physics] ,Eastern Paratethys ,Sedimentary rock ,Progradation ,Geology ,Palaeoenvironmental evolution ,Marine transgression - Abstract
International audience; In the late Miocene, a large inland sea known as the Eastern Paratethys stretched out across the present-day Black Sea - Caspian Sea region. The basin was mostly endorheic and its water budget thus strongly dependent on regional climate. The basin was therefore prone to high-amplitude water-level fluctuations and associated turnovers in water chemistry and fauna. Profound palaeoenvironmental changes happened in the Eastern Paratethys during this time period. This article documents the evolution of the Dacian Basin of Romania, the westernmost branch of the Eastern Paratethys, during the time interval between 7.7 and 6.0 Ma. Our integrated study of sedimentary facies, micro- and macro fauna along the Slănicul de Buzău Section was constrained with a timeframe based on magnetostratigraphy. The remarkable 1.3 km-thick sedimentary record, high depositional rate (0.65-1.26 m/kyr) and abundance of fossils along this section provide a unique opportunity to study sedimentary and biotic turnovers in high detail. Our analyses reveal several marked water-level and salinity changes: A predominance of freshwater coastal plain environments, only occasionally flooded, indicates a low water-level in the Khersonian (~7.7-7.63 Ma). The coastal plain deposits are overlain by offshore muds revealing a low mesohaline early Maeotian transgression, which was followed by the installation of littoral/nearshore environments with freshwater molluscs in shallow settings and oligohaline ostracods in slightly deeper settings. Subsequent delta progradation and a prevalence of freshwater fauna in both marginal and more distal environments characterize the late Maeotian. This was followed by a remarkable freshwater transgression that started at 6.3 Ma and led to predominantly offshore deposition. The late Maeotian fossil record suggests brackish water pulses from Lake Pannon (Central Paratethys), followed by mass occurrences of Coelogonia novorossica. At 6.1 Ma, a short influx of meso- to polyhaline microfauna including benthic and planktonic foraminifera defines the "Pontian Salinity Incursion". Molluscs, including Eupatorina littoralis, that biostratigraphically mark the onset of the Pontian arrived with a negligible delay of ~5 kyr after the microfauna influx. The onset of the Pontian at Slănicul de Buzau at 6.1 Ma (± 5 kyr), is thus synchronous with the onset in other Paratethys basins. Our integrated approach, placing the preserved fossil fauna in its respective sedimentary environment, allows for a detailed insight into the salinity of coeval marginal as well as basinal environments and could be more widely applied in the Paratethys realm and other semi-isolated basins with a deviant salinity.
- Published
- 2020
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