Acoustic evidence of a Baltic Ice lake drainage debrite in the northern Baltic Sea

The sudden drainage of the Baltic Ice Lake (BIL) at the end of the Younger Dryas Chron was one of the major events within the Pleistocene/Holocene boundary in Scandinavia. Thus far the effects it might have had on sedimentary environments have been inadequately recorded outside of central and southern Sweden. In the present study, high-quality acoustic sounding data was used to examine and describe possible traces of the event from the north eastern Baltic proper and Gulf of Finland sediments. Five acoustic facies were identified; two of them bearing frequent indications of sediment deformation, slumping, sliding and homogenization. The lower deformation zone is in the glacial clay deposited in the ice-proximal environment, the middle zone in the ice-distal glacial clay and the upper zone in late-glacial clay. We suggest that the middle deformation unit may have basin-wide significance because it represents a debrite system originating from sediment instability due to the sudden water-level drop associated with the BIL drainage at the transition of the Younger Dryas/Preboreal Chrons.