First direct age determination for the Baltic Ice Lake/Yoldia Sea transition in Finland

Abstract

The drainage of the Baltic Ice Lake (BIL) to the Yoldia Sea level occurred at around 11 600 years ago and can be considered as one of the most important events in the Late-Glacial Baltic Basin history. Distinctive sandy deposits were formed as a result of the water-level fall. These deposits form a marker horizon at the Pleistocene–Holocene boundary, which has been used as the 0-varve in Finnish clay varve chronology. These sandy deposits have not been dated, and in general, there is lack of direct age determinations from the Pleistocene–Holocene transition. Sediments from three localities: backshore, beachface and upper shoreface environments, interpreted to be connected with BIL drainage, were sampled and dated with an optically stimulated luminescence (OSL) method. Only the beachface deposit appeared to be the suitable material, giving the expected dates of 11 400 ± 1100 and 11 200 ± 1300 years BP for the water-level fall. The other samples were interpreted as only partially bleached, or they represented a mixture of different age generations. This is the first direct dating of a Yoldia shore deposit in Finland and provides a reference for shore displacement studies in Finland. The results also verify the potential of the OSL method in dating ancient shorelines or land uplift history.