Paraglacial barrier—lagoon development in the late pleistocene Baltic Ice Lake, southwestern Baltic

Abstract

Marine geological investigations including shallow seismic, sedimentological and stratigraphical studies were carried out in Fakse Bay, southwestern Baltic. Seismic sequence analytical methods were used, supplemented by detailed lithological descriptions, pollen analysis and 14C dating of core material. Detailed correlations between sediment facies units and seismic sequences resulted in the establishment of four depositional sequences: I. Glacial related deposits, II. lagoon/pond and freshwater coastal deposits, III. Lake-bog-lake deposits, and IV. Marine, (sub)littoral deposits. Most attention has been paid to Sequences II and III, showing the development of a transgressive freshwater barrier beach ridge and a following regression. Pollen spectra indicate Allerød and Younger Dryas Chronozone ages (11,500-10,000 14C yrs B.P.) for the development of a sheltered lagoon/pond basin behind the transgressive freshwater barrier beach ridge. The freshwater coastal deposits are interpreted as the southwesternmost marginal deposits of the Baltic Ice Lake and represent the transgression maximum. This transgression maximum reached a level of about 13 m below the present sea level. The final drainage of the Baltic Ice Lake resulted in the development of a sheltered basin behind the former beach ridge. A fluctuating groundwater level here favoured the deposition of alternating lake gyttja and bog peat deposits in the central part of the basin. Pollen analysis and 14C dating reveal that the lake deposits correspond to high groundwater levels associated with the Ancylus Lake (9000 yrs B.P.) and the Littorina Sea (7000 yrs B.P.) transgressions, while the bog sediments represent the low water stands in the early Holocene.