A detailed Middle and Late Pleistocene cyclostratigraphic record using rock magnetism and palaeosol proxies in the Middle Dnieper basin loess domain

Abstract

<p>A combined pedostratigraphic and rock magnetic study of four loess-palaeosol sequences in the Middle Dnieper area, Ukraine (at Gunky, Zamozhne, Vyazivok and Stari Kaydaky) have been performed in order to determine the suitability of these sites for rock magnetic cyclostratigraphy and the establishment of magnetostratigraphic markers. Two geomagnetic events – the Matuyama/Brunhes boundary (at 780 ka) and Unnamed excursion (at 430 ka) – have been detected at the long Vyazivok loess-paleosol record (Hlavatskyi et al., 2016; Hlavatskyi and Bakhmutov, 2020). The till of the Dnipro glaciation (MIS 6) and the corresponding thick loess (U-L2), present in all sections, and faunal remains at the Gunky section, typical for MIS 11 (Markova, 2004), serve as reliable age benchmarks for developing a comprehensive cyclostratigraphic model. The studied sections are most similar by their rock magnetic and palaepedological characteristics to the Hungarian loess-palaeosol sequences (Udvari-U2 and Paks), which are also located in the temperate climatic zone. These sections can be related to the «Chinese» type of formation of magnetic properties, with very low magnetic susceptibility values in loesses and higher values in palaeosols. However, the magnetic susceptibility pattern in palaeosols of northern Ukraine is distorted by the later cryoturbation and gleying processes of the subsequent cold phases. In contrast to the Chinese, Danube and southern Ukrainian loess sequences, these sites are characterized by much lower concentration of ferrimagnetic material, especially in the Lubny (U-S5, correlative of MIS 13) and Potyagaylivka (U-S2/MIS 7) palaeosols. The highest magnetic enhancement is characteristic for the Lower Zavadivka (U-S4/MIS 11), Upper Zavadivka (U-S3/MIS 9) and, in part, the Pryluky­-Kaydaky (U-S1/MIS 5) pedocomplexes. Rock magnetic investigations show predominance of pseudo-single domain magnetite in palaeosols and higher proportion of hematite in loesses. It is suggested that wet conditions in northern Ukraine, which periodically appeared due to its closeness to the ancient ice fronts, facilitated the oxidation of ferrimagnetic grains and the formation of high coercive minerals.</p><p><strong>Acknowledgements. </strong>The research was supported by the National Research Foundation of Ukraine grant 2020.02/0406 "Magnetic proxies of palaeoclimatic changes in the loess-palaeosol sequences of Ukraine".</p><p><strong>