Taxonomic, quantitative and isotopic study of foraminifera from mudstone and claystone xenoliths incorporated into slump facies of the Stratified Salt Member of the Wieliczka deposit shows that the majority of xenoliths represent the CPN 8 biozone (Wielician substage, Badenian, Middle Miocene). The share of the CPN 7 biozone is minor; it was recorded in two of 26 samples analysed. The source area of xenoliths was the basinal part of the Carpathian Foredeep, located far off the shoreline (shallow-water taxa are not present in the samples); it represents the upper bathyal zone, in oxygenated conditions. Inbenthic, eutrophic and opportunistic foraminifers dominate the benthic environment of the CPN 8 span of time. Increased d18O values of the Globigerina bulloides tests (from +1.7‰ in CPN 7 to +2.3‰ in CPN 8 sediments) was due to the change from the Middle Miocene Climate Optimum to the Middle Miocene Climate Transition at the CPN 7/CPN 8 boundary. This palaeoclimate event is the marker of the Moravian/Wielician chronostratigraphic boundary in the Central Paratethys. The Wielician shows the distinct taxonomic reduction of the Moravian planktonic foraminifera and includes the Globigerina bulloides Acme.