Impact of southern Baltic sea-level changes on landscape development in the Verkeån River valley at Haväng, southern Sweden, during the early and mid Holocene

Sammanfattning: In the Hanö bay off the coast at Haväng in SE Scania, southern Sweden, a submerged and well-preserved Mesolithic landscape is found, including remains of trees, river and lagoon sediments, and archaeological artefacts such as an antler pick axe and stationary fishing constructions. The landscape was formed during the Yoldia Sea (11,700-10,800 cal BP) and Initial Littorina Sea (9800-8500) low-water phases of the Baltic Basin. The landscape was subsequently drowned during the Ancylus Lake (10,800-9800 cal BP) and the Littorina Sea (8500-6000 cal BP) transgressions. The present study complements previous work by focusing on landscape development in the part of the Haväng area that is located inside the modern coastline but was influenced by the early to mid-Holocene sea-level fluctuations within the region. The study sites, Öradekaren and Havängsgården, are located approximately 500 m from the coastline, in close proximity to the Verkeån River. Sediment sequences were analysed for pollen and macrofossils in order to reconstruct the development of the vegetation. Sedimentological, geochemical and geophysical methods were used, for example, X-ray fluorescence and magnetic susceptibility, in order to reconstruct the hydrological development at the sites from approximately 11,000 to 6000 cal BP. The analyses revealed a lacustrine environment in both sites, with fluctuating lake levels that from time to time was in connection to the Verkeån River. Within the time period of this study, two major transgressions occurred in the area. The Ancylus transgression peaked at approximately 10,300 cal BP but never reached the two localities, but the profound decline of Pinus pollen in the pollen record at this time reflects the drowning of the predominantly pine-rich forests growing in what today is the Hanö Bay. Another transgression starting at about 9 000 cal BP, peaked at about 5 m a.s.l. between 7500-6000 cal BP. This is above the elevation of the two localities, but due to the narrow river valley, damming of the Verkeån River occurred by sediment ridge build up during the transgression. A sheltered lagoonal environment developed and the freshwater signature was preserved. Erosion and redeposition of older sediments occurred at the Havängsgården, but the Öradekar site remained a relatively deep and sheltered basin. The vegetation surrounding the sites displayed both aquatic and moisture demanding plants in and near the Öradekar Lake and Pinus and various deciduous trees on the drier grounds. After 6000 cal BP the landscape changed, the lakes were overgrown and turned into fens, the number of trees declined and more open ground covered by grasses and herbs developed. This suggests increased human impact on the landscape, including grazing of the recently developed fens at the study sites. This study showed that the impact of the sea level fluctuations during the Littorina Sea was recognised by lagoonal development, drowning parts of the river valley but no traces of saline influences in the study area were found.