The Weichselian in southern Sweden and southwestern Baltic Sea : glacial stratigraphy, palaeoenvironments and deglaciation chronology

Abstract: In this thesis the Weichselian glaciation history of southernmost Sweden and the southwestern Baltic Basin is discussed, with special emphasis on Middle and Late Weichselian ice advances and subsequent deglaciations. The main study area was Kriegers Flak in the southwestern Baltic Sea where pre-Late Weichselian sediments were identified. We suggest that the lowermost till on Kriegers Flak, dated to the Early or Middle Weichselian, was deposited during the Ristinge advance, which implies an age of c. 55-50 ka. Following the deglaciation after this advance, isostatic depression enabled a marine influence in the southern Baltic Basin. During this time Kriegers Flak unit A, with a low-diversity benthic foraminifera fauna indicative of cold water and low salinities, was deposited. This was followed by a forced regression on Kriegers Flak, probably caused by a combination of isostatic rebound and a falling global sea level. Between 42 and 36 cal. ka BP wetlands and shallow lakes existed on Kriegers Flak (unit B). Macrofossil and pollen from this unit suggest tundra-like, or forest tundra-like vegetation, possibly with birch and pine in sheltered locations. From 28.5 to 26 ka, a thick succession of glaciolacustrine clay, unit C, was deposited at Kriegers Flak indicating a damming the Baltic Basin by an ice advance into Kattegat. The upper part of the stratigraphy has been reconstructed from published and new terrestrial sections in Skåne. Here three tills are identified. The lowermost, the Allarp Till, was deposited after the damming of the Baltic Basin at c. 30 ka. It was followed, after a deglaciation, by deposition of the Dalby Till, representing the Last Glacial Maximum advances including an early advance from southeast, the main advance from northeast and the first Young Baltic advances from southeast. The uppermost till, the Lund Till was deposited by the Öresund advance after a deglaciation. The deglaciation of southern Sweden was dated using cosmogenic nuclide surface exposure dating. We suggest that central Skåne was deglaciated between 17 and 16 ka. The deglaciation in southern Småland was dated to 15.6±0.8 and 16.6±0.9 ka, while a site in northern Småland was dated to 14.6±1.0 ka. Our northernmost site, situated only 25 km south of the Younger Dryas Moraine, was dated to c. 13.8±0.8 ka while cosmogenic surface exposure ages from Gotland suggest a deglaciation before 13.0±0.8 ka.