Variable isostatic uplift patterns during the holocene in southeast Sweden, based on high-resolution ams radiocarbon dating of lake isolations - a preliminary interpretation

To describe changes in shoreline configuration in northern Uppland, south-east Sweden, the isolations of 17 present and overgrown lakes have been interpreted from diatom analysis and AMS radiocarbon dates on terrestrial macrofossils. The sites studied are spread c. 60 km in east-west and c. 70 km in north-south direction. The oldest isobase direction, representing the "Neolithic Sea", extends in more or less north-south direction. The present day isobase system shows a clear east-west trend. The results indicate a complicated pattern of isostatic uplift during the late Holocene. We have defined five different shore displacement curves denoted A–E. It is obvious that the present day east-western isobase system is not valid for the investigated sites. Instead, the north-south isobases for the "Neolithic Sea" should to a relatively high degree explain the geographic distribution of sites. It is suggested that a re-direction of the isostatic uplift pattern has occurred sometime during the last c. 5000 years. This shift could have taken place as a slow deformation of the bedrock and/or as neotectonic movements along existing fault lines.