Strandforskyving og isavsmelting i midtre Hardanger

A new Holocene relative sea-level (RSL) curve is drawn, based on three firmly dated isolation basins in mid-Hardangerfjorden, southwest Norway. Several AMS-datings of Betula leaves from each isolation contact yielded very consistent ages. Following deglaciation, RSL at the site fell very rapidly a total of about 70 m during the Preboreal. The regression rate then slowed down considerably during a time span of ca. 1000 years, and a slow and even regression has taken place from then until present. No evidence of the the Tapes transgression is seen in the investigated stratigraphies, although a possible transgression or stillstand of the RSL cannot be ruled out on basis of merely these three isolation basins. The RSL curve is placed together with two other curves from the outer coast, and on this foundation a Holocene shoreline diagram representative for Hardangerfjorden is constructed. A deduced shoreline gradient curve displays a rapid decrease in the tilting of the shorelines (1,4 – 0,2 m/km) during the course of the first ca. 3000 years. From then on, the tilt has been steadily decreasing until present. Marine shells were obtained from the lowermost glaciomarine sediments in the cores. Eight datings were performed, all yielding early Preboreal ages. This indicates a final deglaciation of the area at the transition from the Weichselian to the Holocene, and supports the hypothesis of a glacier occupying Hardangerfjorden some time during the Younger Dryas. The Storegga tsunami is believed to have reached Hardangerfjorden, but no clear evidence has been found for this event