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PALAEOGEOGRAPHY OF LATE GLACIAL AND LOWER HOLOCENE LAKES IN THE POMERANIAN BAY ON THE BASIS OF MALACOFAUNA AND OSTRACODS AND SEISMOACOUSTIC DATA

Jarmila Krzymińska, Piotr Przezdziecki

¹Polish Geological Institute, Branch of Marine Geology, 80-328 Gdańsk, Kościerska 5, Poland; e-mail: jkrzymińska@pgi.gda.pl, pprzezdziecki@pgi.gda.pl

Abstract

Within a small (2.5 x 2.5 km) test field, located in the eastern part of the Pomeranian Bay, the geological structure was investigated in detail using seismoacoustic profiling and coring. In the cores, mineral grain size and micro- and macrofauna were analysed. Basing on seismoacoustic records, three main seismostratigraphic units were distinguished. The lowest unit is built of sand and muddy sand. Higher up lies the unit of sandy mud, in some places – of clay. Fauna assemblages indicate cold climate conditions, and clearly point to an existence of lacustrine reservoir of oligotrophic character. Analysis of cores shows that sedimentation began in bog conditions. The lakes in the area existed till the Atlantic period, when due to sea transgression they became filled with sandy sediments. The third unit is built mainly of fine sand, locally medium sand, even with addition of gravel. Basing on the presence of marine fauna, this unit is classified as marine sand.

Key words: Pomeranian Bay, malacofauna, ostracods, seismoacoustic data