Abstract
The respective environments in two ancient rivers were studied using geochemical methods with paleogeographic reconstructions of fossil material represented by shells of freshwater bivalve mollusks. The studied outcrops are located in the basins of the Dniester and Prut rivers. Materials were collected from two Pliocene (Brînza, Giurgiuleşti) outcrops and the ages of the second group of localities (Sucleia, Slobozia Mare, Gura Bîcului) are from Middle to Late Pleistocene. The determination of the taxonomic position was carried out using standard malacological methods. Geochemical data were used for the environmental reconstruction and included stable isotope ratio and trace element compositions in subfossil freshwater bivalve shell (Bivalvia: Unionoida). Key indicators of paleoenvironments show changes in water temperature. Changes in the taxonomic composition of bivalve mollusk assemblages also occurred. In the present study, increasing the water temperature caused a change of stenobiont species of bivalve mollusks to eurybiont species. Eutrophication of watercourses, caused by anthropogenic pollution and climate change in the direction of warming, has led to the replacement of pearl mussels of the family Margaritiferidae by more eurybiont species of the family Unionidae in the benthic communities of European oligotrophic rivers. These processes are similar to those deduced for the Neogene-Quaternary watercourses of the Prut and Dniester basins, but they proceed at a much faster pace. They are processes of eutrophication of watercourses – the main factor leading to the catastrophically rapid modern reduction of the ranges of pearl mussel.
Highlights
Materials and methodsThe Neogene-Quaternary riverine deposits of the Russian Plain are the focus of attention for geologists, geographers, and paleontologists
An application of geochemical methods to fossil shells of freshwater bivalve mollusks from Neogene-Quaternary localities in the south of the Russian Plain was undertaken in this research
The data obtained in this study indicate the need to develop pan-European programs on the problem of eutrophication of oligotrophic rivers, otherwise, there is a risk of extinction of the remaining populations of pearl mussels in Europe (Bolotov et al 2018)
Summary
Materials and methodsThe Neogene-Quaternary riverine deposits of the Russian Plain are the focus of attention for geologists, geographers, and paleontologists. Geochemical methods are quite effective and represent the analysis of ratios of stable oxygen isotopes (Goodwin et al 2003) and carbon isotopes (Fritz and Poplawski 1974, Latal et al 2004), and an analysis of the content of trace elements in the carbonate of shells (Bolotov et al 2015). Techniques such as laser ablation, for example, allow the detection of changes in hydroclimatic conditions in a waterbody during the life of a mollusk, based on an analysis of the layers in the shell cut (Schöne et al 2010). The main goal of this work was the reconstruction of some parameters of the aquatic environment in the Pliocene and Pleistocene biotopes in the Prut and Dniester river basins
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