Holocene shore displacement and shorelines in Hordaland, western Norway



A new shore displacement curve from Fonnes, ca. 50 km NW of Bergen, and a revised curve from Bømlo, ca. 80 km S of Bergen, are presented, based on pollen and phytoplankton analysis of organic sediments in present and ancient lake basins. The transitions between marine and lacustrine sediments have been radiocarbon-dated. The Fonnes and Bømlo curves are closely related and show a rapid regression between 10,000 and 8,700 years B.P., from 30 m above sea level to ca. 4 m above sea level. A transgression took place between 8,500 and 7,200 years B.P. when the shore level rose to ca. 11 m above sea level. Between 7,200 and 6,000 years B.P. the shore level was almost constant, before a slow regression took place. The earlier interpretation of the Tapes transgression including two shore level oscillations at Bømlo is rejected. A method is presented for constructing an equidistant shoreline diagram on the basis of three radiocarbon-dated shore displacement curves from three areas arranged in a triangle (Fonnes, Sotra, Ostereidet). When followed along the projection plane, a working model of the shore displacement curve from Fonnes and an approximation of the change in shoreline gradient during the Holocene indicate that the transgression maximum is metachronous.