Pollen analysis, chronology and palaeomagnetism of three Late Weichselian sites in southern Sweden

Abstract: Three sites, Torreberga in Skåne, Farslycke in Blekinge and Lake Bolmen in Småland, with Late Weichselian lake sediments were studied with respect to pollen analysis and palaeomagnetism. The chronologies are based on pollen stratigraphical correlations, radiocarbon dating and, for two of the sites, on a clay-varve chronology. The stratigraphies were correlated to the GRIP event stratigraphy and their ages are expressed in calendar years BP. The pollen records compare well to the established Late Weichselian pollen stratigraphy for southern Sweden, and reflect the vegetation development from the deglaciation to the transition to the Holocene. The annual time-resolution of the varved clays has made it possible to calculate pollen accumulation rates based on actual sedimentation rates. The delayed onset of sedimentation in Torreberga implies that dead ice was present for at least 2000 years after the regional deglaciation of the area. Although the clay varve chronologies could not be absolutely dated through connections to the Swedish Time Scale, they have been assigned approximate calendar-year ages based on the pollen stratigraphies and their correlation to the GRIP event stratigraphy. These correlations made it possible to assign calendar year ages for the deglaciation of Blekinge and south-western Småland, and to discuss the deglaciation chronology for southern Sweden with enhanced accuracy. Farslycke and the northern end of Lake Bolmen were deglaciated at c. 14,350 and at c. 14,400 calendar (GRIP) years BP, respectively. Palaeomagnetic secular variation records for the three sites are presented. Among the series of directional changes, the main characteristic, which can be found in all stratigraphies, is a broad westerly declination swing between c. 13,000 and 12,000 calendar years BP. This swing can be recognised in other records from southern Sweden and in Estonia.