A Holocene sea-level curve and revised isobase map based on isolation basins from near the southern tip of Norway

We report a new Holocene relative sea-level curve based on the stratigraphy in five closely located isolation basins near Lista in southernmost Norway. The results detail the progress and timing of the mid-Holocene Tapes transgression, the peak of which in this region represents the highest postglacial sea level, as well as the rate of land emergence since then. One additional cored basin is situated above the marine limit. All the basins have bedrock sills that were levelled using a differential GPS. Isolation and ingression boundaries were identified by macrofossil analysis and radiocarbon dated on terrestrial plant remains. In most cases several dates were obtained from each transition. Relative sea level rose with a mean rate of 7 mm a−1 during the last part of the Tapes transgression 8600−8200 cal. a BP and then gradually slowed to a mean rate of 1 mm a−1 from 8200−7000 cal. a BP. Mean sea level reached ∼5 m higher than the present level when the transgression culminated. Land emergence took place after this, first slowly at a mean rate of 0.4 mm a−1 until ∼3900 cal. a BP before it increased to 2.6 mm between 3900 and 3400 cal. a BP. Since then it has slowly decreased until today and has been ∼0.2 mm a−1 for the last 2000 years. Based on the new curve we present updated Tapes isobases for the region that are displaced by ∼20 km in relation to the existing model. From one basin we also report a 5-10 cm thick layer of sorted, sandy gravel, embedded in a more than 5-m-thick deposit of homogeneous shallow-marine mud. The gravel was deposited ∼5500 cal. a BP, which is the same age as a tsunami deposit previously mapped in Shetland. As several typical characteristics of tsunami facies deposits are lacking, the origin of the gravel layer remains inconclusive.