Late middle Pleistocene malacological evidence of loess deposition in southeastern Poland and western Ukraine

Abstract

About a dozen sites from the Late Middle Pleistocene, including loess attributed to MIS 6 (L2 loess) and MIS 8 (L3 loess), have been described in southeastern Poland and western Ukraine. Mollusc shells were found in thirteen profiles (four sites in Poland and nine in Ukraine). The occurrence of 26 taxa and over 22,500 specimens was recognised. The malacological analysis allowed us to distinguish five types of mollusc assemblages with different taxonomic composition and ecological structure, indicating the variability of depositional conditions of the discussed sediments. The defined assemblages were characterised by the occurrence of open-country taxa representing dry (Pupilla loessica, Pupilla muscorum and Vallonia tenuilabris) or humid (Succinella oblonga elongata and Trochulus hispidus) environments. Fauna typical of habitats with high humidity (with Vertigo genesii and Vertigo parcedentata) and aquatic (with Gyraulus laevis and Galba truncatula) occurred much less frequently. The ecological structure and taxonomic composition of the malacofauna occurring in the L2 and L3 loess showed great similarities. This implies similar climatic and environmental conditions on a sub-continental scale (Central Europe at the northeastern foreland of the Carpathians) during the Late Middle Pleistocene. In this context, the main contributors to the diversity of malacocoenoses are: (i) continental/regional factors (physical-geographical, climatic, i.e. succession of climatic phases: colder, warmer, drier and wetter, during glacial periods and related phases of intensified loess deposition interspersed with periods of increased pedogenesis), (ii) orographic/morphological barriers, and (iii) local conditions prevailing in specific geographical regions or even near the particular profiles (relief and microrelief, insolation, water conditions).