Sedimentary record of a late Saalian jökulhlaup: Case study in SiedlÄ tków outcrop, Central Poland

Characteristic features of the analysed jökulhlaup deposits include erosional and deformational contact with the substrate, a high content of very coarse sediments, poorly sorted with predominant massive clast-supported gravels and boulders, the presence of rip-up clasts, inverse grading in the lower part of the profile, normal grading in the upper part, and similarities in clast shape and roundness and the ratio of local rocks to Northern origin rocks when compared to the surrounding Saalian till. The documented features allow for the following phases of jökulhlaup to be distinguished: initial, rising, high stage, and waning stage. During the reconstructed event, hyperconcentrated flow was dominant, whereas fluvial flow and debris flow were of lesser importance. The release of meltwater in the marginal part of the ice sheet came from the depression of the Koło Basin, to the north of the analysed sites. Complex deformation processes which occurred in the flood deposits and their substratum were also interpreted. The analysed jökulhlaup event resembles some minor glacial floods in the ice-contact zone of present-day Icelandic glaciers. Further research in marginal zones of Pleistocene ice sheets should account for their occurrence, as the analysed example indicates that jökulhlaups might have had considerable influence on the course of sedimentation processes in the marginal zones of ice lobes of Pleistocene ice sheets as well as in the marginal valleys and sandars.