A Comparison of Eemian and Holocene Transgressions of the Baltic Sea based on the Sedimentary Record of Lake Ladoga
Abstract:Two cycles of postglacial transgressions of Baltic Sea could be recognized in the sediments of Lake Ladoga and vicinity: an Eemian (MIS 5e, ca 124-119 kya) and a Holocene with several subsequent stages: Ancylus Lake, Mastogloia Sea and Littorina Sea, starting at ca 9.5 kya BP and existing up to 4 kya BP. New data obtained from deep coring in Lake Ladoga (Andreev et al., 2014) has allowed us to re-visit an old question about the age and nature of sediments at the bottom of Lake Ladoga. The lake is east of the Baltic and provides important information about the marginal stage of Baltic Sea levels, and in particular about differences between the Eemian and Holocene transgressions.
Previously Eemian marine sediments have never been found at the bottom of Lake Ladoga although they have been identified along river terraces, in small lakes and as detached lenses. The new coring reached a depth of 22 m, and found marine diatoms that might correspond to the Eemian transgression. As part of the effort to understand these fossils, we have compiled a comprehensive picture of the distribution of Eemian sediments around Lake Ladoga. There is very little published data about these deposits (Miettinen et al., 2014) so we have assembled known, but never published or published only in Russian, data.
The number of unpublished marine Eemian sequences exceeds 70. They occur more frequently here than on other Baltic coasts, because of the low position of the eastern Baltic territories above the sea level. This meant that they were not destroyed by isostatic uplift, which resulted in the deposition of thicker layers of sediment than in mountainous Fennoscandia. Typical Eemian sediments comprise a black clay layer with Yoldia arctica, have a monotonous appearance and are easily distinguished from other interglacial sediments. The modern elevation of these sections implies that the elevation of the Eemian Sea could not have exceeded +17 m and probably was very uniform.The Holocene sediments are found extensively around the Lake and on its bottom, and have been well-studied, which makes it possible to reconstruct in detail the transgressions of the Baltic Sea at the beginning of the Holocene. We hypothesize that a similar scenario was associated with the Eemian transgression and this allows us to provide a better interpretation of our data.