CLAY MINERAL ASSEMBLAGES IN THE WESTERN BALTIC SEA - RECENT DISTRIBUTION AND RELATION TO SEDIMENTARY UNITS

Surface samples and nine cores from the western Baltic Sea and margina l water bodies were investigated for clay mineral composition. The cla y mineral assemblages of recent sediments are rather homogeneous. Vari ations result mainly from the erosion of different glacial source depo sits. High percentages of illite and low kaolinite/chlorite and quartz /feldspar ratios are characteristic for this glacial source. Advection of kaolinite-rich suspensions from the North Sea is believed to accou nt for higher kaolinite/chlorite ratios in the Mecklenburg Bight. A co ntribution of the rivers Trave and Oder to the western Baltic Sea is i ndicated by increased smectite values in marginal water bodies. They c orrespond to increased kaolinite/chlorite and quartz/feldspar ratios. In the main basins the river signal is diluted beyond recognition. Cor es from the Arkona, Bornholm and Gotland Basins penetrate through post -littorina muds and sediments of the Ancylus Lake/Yoldia Sea into Late Glacial sediments or the Baltic Ice Lake. Clay mineral assemblages ar e characterized by an increase in kaolinite/chlorite ratios from I,ate Glacial to Holocene sediments, with a distinct shift at each facies c hange. This allows the distinction and core to core correlation of mai n lithological units with kaolinite/chlorite ratios. Kaolinite enrichm ent of Holocene muds corresponds to a brackish-marine facies and may r eflect influx of kaolinite-rich suspensions from the North Sea. Cores from the lagoon of the Oderhaff show fluctuations in the contributions of the two main sediment sources: river suspersion and glacial deposi ts during the Late Glacial and Postglacial sequence. Lacustrine sedime nts, which were deposited prior to 5500 years B.P. are characterized b y smectite, kaolinite and quartz from the drainage area of the Oder ri ver. Erosion of coastal and offshore glacial boulder clays with the Li ttorina transgression supplied a marine component rich in illite, chlo rite and feldspars to the brackish muds of the Oderhaff. (C) 1997 Else vier Science B.V.