The Ancylus and Litorina transgressions of the Baltic in southwest Finland

Abstract

The extent and age of the Ancylus and Litorina transgressions in the Salpausselkä (Younger Dryas) end moraine zone of southwest Finland were studied by means of morphology and radiocarbon dated biostratigraphical studies of isolation basins. The rapid regression in the Baltic between ca. 10.2 and 9.7 ka BP (Yoldia regression) was followed by the Ancylus transgression, which involved a 2–8 m rise in water level in the research area. The rise has been identified in 10 basins and has been dated to the Betula pollen zone, from 9.7-9.5 to 9.2-9 ka BP. The rise in water level has not been identified inland of the 3rd Salpausselkä moraine, and it is concluded that the area north of this moraine lay beyond the limits of the transgression. The amplitude of the transgression decreases from 8 m in the SE to 2 m in the NW, whilst the shoreline associated with it (Ancylus I) rises from 62 m to 82 m with a gradient of about 0.4–0.5 m/km. The following Ancylus regression was initially rapid but became slower at ca. 8.5-8 ka BP, when the rate of land uplift became nearly as high as the rise in water level in the study area. The subsequent Litorina transgression, involving a rise in water level of 1–4 m, was dated to the beginning of the Atlantic (7 to 6.4 ka BP). The transgression has an amplitude of 1–2 m in Bastukärr basin, which lies between the 1st and 2nd Salpausselkä end moraine zones. The shoreline associated with the transgression (LI) varies from 35 m in the SE to 45 m in the NW with a gradient of about 0.15-0.2.