Refined magnetostratigraphic position of the Shyrokyne unit in loess sequences from Central Ukraine

Abstract

The youngest geomagnetic polarity reversal, the Matuyama–Brunhes boundary (MBB), which occurred 780 kyr ago, is a “golden spike” in the age calibration of sediment sequences. The use of palaeomagnetic method as a stratigraphic tool in the study of loess sequences from Ukraine originated some 50 years ago. One major problem in using the available data is the contradictory position of the MBB in different stratigraphic units, which affected historic evolution of the chronostratigraphic models of the Quaternary in Ukraine. The most important units in this regard are the Shyrokyne and Martonosha units, in which the MBB had been defined most often. This paper provides the careful analysis of the previous magnetostratigraphic data and new preliminary results from key loess-palaeosol sections in Central Ukraine. Shyrokyne palaeosol complex in four loesspalaeosol sections located in the Middle Dnieper and Podolia regions has been palaeomagnetically studied. It is shown that the transition zone of the Matuyama–Brunhes palaeomagnetic reversal is most likely located at the base of the soil complex. In the Vyazivok section the MBB has been found in the lowermost part of Shyrokyne palaeosol sh1. Preliminary palaeomagnetic studies of the Stari Kaydaky section reveal that the MBB cannot be defined at least above sh1 subunit. Medzhybizh and Holovchyntsi sections were deposited after the Matuyama–Brunhes reversal; however, the palaeomagnetic informativeness of the part of studied strata is doubtful. Magnetostratigraphic position of the Shyrokyne unit below the MBB in some previous studies is explained by methodological reasons and inconsistent chronostratigraphic models. The paper substantiates that normal magnetic polarity zone in the Pryazovya loess and upper part of the Shyrokyne soil is not associated with the influence of secondary processes on the palaeomagnetic record.