Paleoenvironmental implications of grain size characteristics of loess key-sites from opposite banks of the Middle Dnieper River valley (Ukraine)

The loesses of central Ukraine, occurring on both sides of the submeridional-oriented Dnieper River valley, have the character of continuous patches up to 30 or even 50 meters thick. In geological exposures (mainly cliffs) they have the character of loess-palaeosol sequences, additionally separated by glacial till (Saalian), which plays an important role as a stratigraphic marker. The loess cover underlies the river sediments of the Pleistocene Dnieper terraces. A characteristic feature of the documented sequences is a clear difference in their thickness, as well as litho- and pedological formation on opposite banks of the Dnieper River.

Grain size analyses (laser and sieve) of a number of sequences on both sides of the river were conducted. The assumed constant interval was 5 cm. Based on the measurements, accurate statistical characterization of the individual fractions and subfractions was developed and a number of indices were calculated that may be of great value in environmental interpretations.

Paleogeographic conclusions from sedimentological studies were focused on the characterization of depositional environments. The basic conclusion is the documented great dissimilarity of grain size characteristics of lithological units of the same age on both sides of the Dnieper valley. This reflects the different nature and high variability of environmental conditions during accumulation period. The study clearly shows that the valley was an important source of windblown silty material, but also its morphologically diverse banks were important orographic barriers for aeolian transported material. Moreover, a strong connection between the investigated aeolian sediments and the older, underlying layers of different origin – glacial and fluvial – was demonstrated.

Research carried out as part of the grant of National Science Centre, Poland as the project no. 2018/31/B/ST10/01507 entitled “Global, regional and local factors determining the palaeoclimatic and palaeoenvironmental record in the Ukrainian loess-soil sequences along the Dnieper River Valley – from the proximal areas to the distal periglacial zone”.