Seismoacoustic profiles from the Arkona Basin show a late Pleistocene and Holocene succession of several distinct reflectors. The physical, sedimentological, mineralogical and geochemical properties of more than 30 sediment cores were analysed in order to assign these reflectors to specific sedimentary discontinuity layers. Additionally, AMS 14C data and biostratigraphic information were gathered. Based on this multi-proxy approach, seven lithostratigraphic units (Al, AII, B to F) were distinguished. These consist of fine-grained clay, silt and mud, and are separated from each other by thin basin-wide traceable sandy layers (Sab-Sef). The most sensitive parameter to mark the lithostratigraphic boundaries is the weight percentage of the grain-size fraction >63 μm. In addition, some of the quartz-grain-dominated sandy layers cause the strong reflection lines recorded in seismoacoustic profiles. The sandy layers are interpreted to reflect enhanced hydrodynamic energy induced by episodes of basin-wide water-level low-stand conditions. These low stands resulted from water-level drops that occurred frequently during the Baltic Sea's history and presumably affected the entire Baltic basin. The thick fine-grained units AI, AII to F, in which coarser material is absent, represent water-level high-stands. We conclude that the units AI and AII are Baltic Ice Lake sediments deposited before and after the Billingen-1 regression, respectively. We assign the most prominent sandy layer Sab to the final drainage of the Baltic Ice Lake (Billingen-2), whereas the sandy layers between units B, C, D and E are related to the Yoldia Sea and Ancylus Lake regression of the Baltic Sea's history. The uppermost fine-grained unit F with its high organic carbon content contains marine sediments deposited after the Littorina Transgression. The macroscopically well-visible sediment colour change from reddish/brown-to-grey, previously interpreted as a regional stratigraphic boundary, varies from core to core. It has been shown by our new data that this colour change has a diagenetic origin, and thus does not represent a stratigraphic boundary. Previous subdivisions therefore have to be revised.
|Status||Udgivet - jun. 2002|
- Programområde 5: Natur og klima