Regressions and transgressions of the Baltic basin reflected by a new high-resolution deglacial and postglacial lithostratigraphy for Arkona Basin sediments (western Baltic Sea)

Seismoacoustic profiles from the Arkona Basin show a late Pleistocene and Holocene succession of several several distinct reflectors. The physical, sedimentological, mineralogical and geochemical proper-ties of more than 30 sediment cores were analysed in order to assign these reflectors to specific sedimentary discontinuity layers. Additionally, AMS C-14 data and biostratigraphic information were gathered, Based on this multi-proxy approach, seven lithostratigraphic units (Al. All, 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 (S-ab-S-ef). The most sensitive parameter to mark the lithostratigraphic boundaries is the weight percentage of the grain-size fraction >63 mum. 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 Al, All to F. in which coarser material is absent, represent water-level high-stands. We conclude that the units Al and All are Baltic Ice Lake sediments deposited before and after the Billingen-1 regression. respectively. We assign the most prominent sandy layer S-ab 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 regressions 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.