Grain-size and geochemical investigations on the Novyi Tik site (NW Ukraine) and their significance for understanding the local sedimentary environment in the Pleistocene

Abstract

Grain size and geochemical composition of the loess-palaeosol sequences are important evidence of the sedimentary environment in the Pleistocene, which enables to revela- tion of the sedimentation rates, the origin of deposits, and the sources of material that contributed to the loess accumulation and pedogenesis. The Kd index (10-50 μm / <5 μm), and the Ti/Zr, Ti/Nb and Ce/Y ratios considered to be indicators of aeolian silt accumulation, whereas the ratio of physical sand to physical clay have been suggested to reveal the relationship between sedimentation and pedogenesis. The grain size and geochemical analysis were applied at the Novyi Tik section (Volyn’ Upland), which is characterized by detailed stratigraphy and lateral diversity of palaeosols and deposits. Based on grain size and geochemical data from the section, four main units have been distinguished, which represent periods with similar sedimentary environment such as MIS 10-7, MIS 6, MIS 5 and MIS 4-2. During MIS 9 and 7, pedogenesis pre- vailed with a slight sedimentary contribution; during short-term cooling, thin loess beds were formed. High loess accumulation rates occurred during MIS 6, however, the source of aeolian dust material was different from those to other loess units. At the end of MIS 6, a period of dynamic sedimentation began, which resulted in the sandy grain-size composition of soils and non-soil deposits of MIS 5. The highest sedimentation rates presumably occurred during the stadials, therefore the soils could inherit the grain-size composition of the parent material. Moreover, during MIS 5 in the valley of the Styr River, episodes of aeolian sand accumulation could take place, since the sandy grain-size composition of soils of that time is widespread throughout the basin of the modern Khrinnyky reservoir. At the end of MIS 5, abrupt changes occurred in the sedimentary environment: sand sedimentation almost ceased and a period of aeolian silt accumulation began, and proceeded until the Holocene.