EARLY HOLOCENE SHORE DISPLACEMENT AND EVIDENCE OF IRREGULAR ISOSTATICUPLIFT NORTHWEST OF LAKE VANERN, WESTERN SWEDEN

In the 1920's the Swedish geologist Lennart von Post found evidence of irregular early Holocene isostatic uplift in the region northwest of Lake Vanern in western Sweden. von Post based his conclusions on level lings of ancient shore lines. These were indirectly dated by pollen st ratigraphical investigations in basins situated at approximately the s ame altitudes as the shore lines. To test von Post's hypothesis, we ha ve adopted a different methodological approach. The sediments in twelv e small lake basins, within five minor areas in this region, have been investigated with respect to when they became isolated from ancient L ake Vanern. Initially all the lake thresholds were levelled. Altitudes range between 165 and 96 m above sea level. By combining the results of mineral magnetic and diatom stratigraphical analyses it has been po ssible to determine the level in the sediment when the basin became is olated. The C-14 age of this isolation level has been inferred from AM S dates based on the NaOH-soluble fraction of bulk sediment, partly wi th very low organic content. Altogether, 36 radiocarbon datings have b een carried out, ranging from 10080 to 8800 C-14 years BP. Pollen anal yses, and subsequent correspondence analysis (CA) of all pollen spectr a, were carried out around the isolation level in each basin as a comp lement to the AMS datings. If the region had been subject to irregular isostatic uplift, lakes at the same altitude in the five areas should have been isolated at different times. The AMS determined isolation a ges, 'corrected' according to CA of the pollen stratigraphy and compen sated for the relatively higher rebound of the northerly situated site s support von Post's conclusion, from the beginning of this century, t hat the region northwest of Lake Va;nern has been subjected to irregul ar isostatic uplift.