The isolation of Kruunuvuorenlampi, southern Finland, and implications for Holocene shore displacement models of the Finnish south coast

In the southern coastal area of Finland, many studies exist on shore displacements related to the higher Ancylus Lake and Litorina Sea altitudes. However, the late- Holocene shore displacement history is much less known and the shore displacement models are based on interpolations. Kruunuvuorenlampi, a small lake located at an altitude of 8.6 m a.s.l., was studied to test the reliability of the interpolated models. The cores revealed an unusual bottom lithostratigraphy, with a coarse gravel and sand layer sandwiched between the lower marine clays and upper shallow-water clay-gyttja. Analysis of diatoms, pollen and loss-on-ignition, together with radiocarbon datings, were carried out to determine and date the isolation event of the lake. The results show that the lake was isolated ca. 2400 ¹⁴C years BP and that the coarse grained layer was deposited prior to the isolation. The reconstruction of the emergence of the lake basin area suggests that the coarse grained layer originated from strong wave erosion of the shores before the isolation. This interpretation is supported by the presence of a wave-washed boulder belt on the NE slope of the basin. The isolation of Kruunuvuorenlampi lies exactly on the interpolated shore displacement model of the 30 m Litorina isobase. This placement suggests that no significant transgressions took place between the Litorina transgression and the isolation of Kruunuvuorenlampi.