Holocene shore displacement and chronology in Ångermanland, eastern Sweden, the Scandinavian glacio‐isostatic uplift centre

Abstract

The shore displacement during the Holocene in southeastern Ångermanland, Sweden, has been investigated by means of radiocarbon‐dating of isolation intervals in sediment cores from a total of nine new basins. Results from earlier investigations have been used in complement. There is a forced regression in the area from c. 9300 BP (c. 10500 cal. yr BP) until c. 8000 BP (c. 9000 cal. yr BP), on average c. 8 m/100 years, after which there is a gradually slowing regression of c. 2.5–1.0 m/100 years up to the present time. The most rapid regression occurs during the later phase of the Ancylus Lake stage, 9500–9000 cal. yr BP. There is no evidence of halts in the regression. Crustal uplift in the area since deglaciation is c. 310 m. The deglaciation of southeastern Ångermanland took place c. 9300 BP (c. 10500 cal. yr BP); this is c. 900 years earlier than the age given by clay varve dating. The shore displacement curve provides a means of estimating the difference between the clay varve time scale and calibrated radiocarbon dates, by comparison with varve‐dated altitudes of alluvial deltas of the River Ångermanalven. From c. 2500 to c. 8000 cal. BP there is a deficit in clay varves of some 300 years; further back in time this discrepancy increases significantly. The main explanation for the discrepancy is most likely lacking varves in the time‐span 8500–10200 cal. yr BP, located along the upper reaches of River Ångermanalven below the highest shore level.