Ascertaining the lithological boundaries of the Yoldia Sea of the Baltic Sea : a geochemical approach

Abstract: When analyzing sedimentary sequences, results which are based solely on macroscopic observations, can lead to misleading and incomplete conclusions. Therefore these observations need to be complemented by analyses on a microscopic or atomic scale, such as through biological, chemical or physical methods. This approach is especially necessary when analyzing marine sedimentary cores from the Baltic Sea. The Baltic Sea development following the deglaciation of Scandinavia has been widely studied and debated and this has concluded in the establishment of four developmental stages: the Baltic Ice Lake, the Yoldia Sea, the Ancylus Lake and the Littorina Sea. However not all of these stages have characteristics which make it easy to identify them in sedimentary sequences, especially in the case of the Yoldia Sea. Therefore, the aim of this thesis was to analyze the Yoldia Sea stage and especially its boundaries to the late Baltic Ice Lake and early Ancylus Lake, by using macroscopic observations and geochemical methods, namely X-ray fluorescence and biogenic silica analysis. These analyses were performed on three different cores originating from the Western Gotland Basin, the Eastern Gotland Basin and the Bornholm Basin. In a first step, the sedimentary cores were described, developmental stages were identified and boundaries between Baltic Ice Lake and Yoldia Sea and Yoldia Sea and Ancylus Lake were discerned. These results were then compared to the identification of developmental stages and their boundaries, established by correlating element ratios, calculated from the chemical data retrieved by XRF analysis, and magnetic susceptibility. In a further step, biogenic silica was analyzed. The macroscopic observations led to the identification of the boundaries of Baltic Ice Lake to Yoldia Sea and Yoldia Sea to Ancylus Lake, yet the marine ingression phase giving the Yoldia Sea its name, could not be identified. This stands directly in comparison to the results of the correlation of element ratios, in which the marine ingression phase could be identified confidently, however the boundaries of Baltic Ice Lake to Yoldia Sea and Yoldia Sea to Ancylus Lake only with caution. Additionally, all three cores, originating from different parts of the Baltic Sea basin, had different depositional influences and thus differed considerably. Very low amounts of silica were yielded when performing biogenic silica analysis, which is in accordance with the literature.