Dumpstones as records of overturning ice rafts in a Weichselian proglacial lake (Rügen Island, NE Germany)

Abstract

Dumpstones and dropstones up to 0.8 m in size occur in a silty/sandy Weichselian glaciolacustrine succession near Dwasieden on Rugen Island in the SW Baltic Sea (NE Germany). The deposits are exceptional because two levels of dumpstones and dropstones are present, suggesting two dumping phases interrupting characteristic fine-grained glaciolacustrine sedimentation. Plastic downwarping of sediments below the dumpstones and dropstones result in soft-sediment deformation structures. The distribution and orientation of the long axes of the clasts are useful tools for the reconstruction of the state of the lake bottom, as well as for the water depth. The horizontal position of the gravels and boulders (parallel to the bedding) suggests deposition in relatively shallow-water. The dumping events are linked to iceberg rafting in a glacial lake during the Weichselian Glaciation (MIS 2).