Holocene palaeoecological changes recorded in mollusc-bearing cave sediments, the Cave above the Słupska Gate (southern Poland)

The Cave above the Słupska Gate (southern Poland) contains about 2m depth of mollusc-bearing deposits. Radiocarbon and archaeological dating indicate that these deposits accumulated during the Holocene (Preboreal to Subatlantic), although the earliest layers may date from the end of the Pleistocene. Eight layers of silts, sands and loess-like deposits were distinguished at the site. Seven of them contained identifiable snail shells, sometimes in large numbers, and sparse remains of vertebrates and archaeological artefacts. The molluscan assemblages retrieved from the cave contain over 40 taxa and 1,200 specimens. The balance of species distributed among 11 zoogeographical groups enabled us to identify four assemblages which differ in their ecological structure and in the composition of the fauna. The oldest fauna (Late Glacial/Preboreal and/or Preboreal) with many shade-loving species is typical of a cool climate. Episodes of drying are evidenced by the loess-like deposits and the occurrence of open-country snails such as the glacial relic Vallonia tenuilabris. This species disappeared in the younger part of the Early Holocene, which is the most distinctive feature of the Słupsko Hill sequence. The Middle Holocene climatic optimum is characterised by abundantand diverse fauna which is typical of mixed and deciduous forests with distinct oceanic influences. The criticalDiscus ruderatus and Discus rotundatus succession reflects the general trends in European malacofaunas. The Late Holocene record may bear some hiatuses, but the shift away from a complete forest fauna is evident.