Magnetostratigraphy and mag netic sus cep ti bil ity of the best de vel oped Pleis tocene loess-palaeosol se quences of Ukraine: im pli ca tions for cor re la tion and pro posed chronostratigraphic models. Geo log i

In Earth’s geological evolution the Vendian is significant because: 1) it preceded the «Cambrian Evolutionary explosion» when the multicellular organisms became suddenly much more diverse; 2) it is associated with the global tectonic and palaeogeographic restructuring of supercontinents, a change in geomagnetic field generation and other global processes affecting different layers of the Earth. At the same time, recent publications indicate an extremely irregular behavior of the geomagnetic field in the Vendian, which significantly differs from the recent regime of the geomagnetic field generation. New information on the configuration and magnitude of the geomagnetic field is crucial for understanding the reasons that can cause different modes of geodynamo. The article describes the new results of palaeomagnetic studies of the Volyn traps — basalts and tuffs of the Volyn series with ages about 560—580 My. The determined palaeodirections and palaeopoles are in good agreement with the previously published data of other authors and substantially complement them. The ChRM-component of «low-titanium» basalts was isolated in high-temperature (>500 °C) and characterized as primary. The same samples were used for palaeointensity determinations which showed the extremely low values of the geomagnetic field — an order of magnitude lower than the present one. The ChRM-component of «high-titanium» basalts was yielded in the temperature range of 200—400 °C. No results were obtained from palaeointensity experiments, and the complex nature of remanent magnetization remains unclear. The new data are compared with the palaeo-magnetic data of the Vendian—Early Cambrian poles of the East European Platform determined by other authors. To test the hypothesis of an anomalous Ediacaran magnetic field characterized by a low dipole moment and a high inversion frequency, more data are necessary. These data can be obtained from the studies of a stratigraphically more complete section of the Volyn traps opened by boreholes. These results will be presented in the next part of the article.

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Variations of rock magnetic parameters in loess-palaeosol sequences, related to climatic and environmental conditions during their formation, are a powerful tool for palaeoclimate reconstruction. Combined enviromagnetic study of loess deposits in Ukraine and its assessment for the palaeoreconstruction purposes are carried out in the framework of the National Research Foundation of Ukraine project 2020.02/0406 ‘Magnetic proxies of palaeoclimatic changes in the loess-palaeosol sequences of Ukraine’. Environmental/climatic reconstructions of the past are fulfilled using a significant number of palaeoindicators: morphology and lithological properties of palaeosols and loesses, their pollen assemblages and a wide range of magnetic characteristics. In this paper, we present a multi-proxy approach to palaeoenvironmental reconstructions, and introduce preliminary results obtained from magnetic susceptibility of loess-palaeosol sequences in the northern (at Vyazivok), central (Stari Kaydaky) and southern (Roksolany) parts of the Ukrainian loess belt. The amplitudes of palaeoclimate change established using magnetic proxies are well correlated with the lithological, palaeopedological and palynological patterns of the sites, and with the global oxygen-isotope scale (MIS). Ongoing studies of the Stari Kaydaky section confirm the correlation of the Upper Zavadivka (S3) soil unit and Lower Zavadivka (S4) soil unit with MIS 9 and MIS 11, respectively (this was proved earlier at the Vyazivok and Roksolany sites). The underlying Lubny (S5) pedocomplex likely corresponds to MIS 13, and the Martonosha (S6) pedocomplex to MIS 15. Palaeomagnetic investigations at Stari Kaydaky have not so far reached the Lower Shyrokyne unit, in which the Matuyama—Brunhes boundary has been detected at Roksolany and Vyazivok. The Upper Shyrokyne (S7S1) palaeosol unit has normal polarity and is preliminarily correlated with MIS 17.

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