Development of a Litorina Bay at Epoo, near Porvoo, southern Finland

HAILA, HEIKKI, SARMAJA-KORJONEN, KAARINA and UUTELA, ANNELI, 1991: Development of a Litorina Bay at Epoo, near Porvoo, southern Finland. Bull. Geol. Soc. Finland 63, Part 2, 105—119. A sediment sequence at Epoo, municipality of Porvoo, on the South coast of Finland, altitude 25 m a.s.l., was studied for Holocene shoreline displacement in the Baltic Sea basin. The sediment sequence is made up of sand, clay-gyttja and drift peat deposited during the Ancylus and Litorina stages of the Baltic Sea. Two cores of clay-gyttja with an intervening sand layer were analysed for diatoms and pollen. The composition of the diatom flora changes from typical fresh-water species of the Ancylus Lake to brackish-water flora indicating transition to the Litorina Sea. The sequence shows a gradual change of a group of separate islands in the Ancylus Lake to larger complexes of dry land because of uplift. As two necks of land were formed, the site developed into a sheltered brackish-water bay, and drift peat accumulated. A radiocarbon age of 6130 ± 50 yr BP obtained from the top of the drift peat links the shore with the Litorina regression. The shore displacement history of the Helsinki-Porvoo area is discussed.