The biostratigraphy of sediments deposited in the Lake Kaali meteorite impact structure, Saaremaa island, Estonia

The results of lithological, biostratigraphical and chronostratigraphical studies on the Lake Kaali meteorite impact structure, Estonia (lat 58°22' N, long 22°40' E) are discussed. Two pollen diagrams and 18 radiocarbon dates from different materials are presented. Due to the small area and deep slopes, Lake Kaali bottom sediments are mixed with allocthonous mineral matter, humus, plant remnants and woody pieces. Pollen records (the extraordinarily high value of Betula pollen in the lowermost spectra, the low Picea pollen frequency and the Quercus pollen maximum) indicate that the meteorite impact catastrophe occurred at about 4000 BP. Soon afterwards the crater ring wall was inhabited by Bronze Age man. At about 2900‒2500 BP, the crater lake dried out and the formation of gyttja was replaced by woody peat accumulation. A return to deepwater conditions at the end of the Early Subatlantic chronozone is marked by deposition of clayey calcareous gyttja