Ostracod assemblages indicating a low water level episode of Lake Peipsi at the beginning of the Holocene

Three sediment cores from the northern part of Lake Peipsi in eastern Estonia were analysed for their ostracod content. The investigated sediments consist of late Weichselian glaciolacustrine varved and homogeneous clay, lake marl, and gyttja. Altogether eight freshwater ostracod species were identified. The distribution of ostracods in L. Peipsi deposits is mostly limited to the lake marl interval. Ostracods made their appearance in shallow-water conditions and were represented by species preferring cold water. The continuous presence of Ilyocypris bradyi refers to the existence of a shallow body of water through the whole period of marl accumulation. Two sediment intervals where Herpetocypris reptans is present and Darwinula stevensoni is absent are interpreted as regressional episodes during the low lake level stage, which were possibly caused by a temporary warming accompanied by increased productivity. Water level in L. Peipsi during the late Weichselian–Early Holocene was ca 10 m lower than at present. According to palynological and radiocarbon data, lake marl with the presence of calcareous fossils started to accumulate at the Younger Dryas–Preboreal transition and continued through the entire Preboreal Chronozone.