Palaeoenvironment during Preboreal-Boreal in Närke, south central Sweden

Abstract

Abstract Four sites have been investigated to illustrate the shore displacement and vegetation history during the Yoldia Sea stage in an area east of the Narke Strait. Diatom analysis shows that two of the localities at 165–170 m and 147 m altitude were located above the highest shore line formed during the Yoldia Sea stage, and that only freshwater diatom assemblages were registered in the sediments deposited during the Preboreal and Boreal chronozones. Acidification of the water seems to have taken place rather early according to the composition of the diatom flora. The basin Ladfallet at 142 m was situated slightly above or at the Yoldia limit, and might have been temporarily influenced by the Yoldia Sea as the diatom flora contains the slightly brackish littoral taxon Mastogloia smithi v. lacustris Grunow. The basin Skelnabackakarret at 127 m was isolated from a bay of the Yoldia Sea, which is clearly reflected by the brackish marine diatom flora. The composition of the pollen flora illustrates that the isolation occurred during the Betula-Empetrum pollen assemblage zone. Radiocarbon datings of the sediments deposited at the isolation gave too high ages, but the spread of Corylus and Alnus were dated approximately 9400 and 8500 BP, respectively. The pollen flora at the four sites studied indicates a vegetational succession from open herb and shrub communities with Betula nana and Empetrum followed by a phase of open birch forests with Juniperus before the immigration of Pinus, Corylus and Alnus.