Palaeoenvironmental investigation of the Warsaw Ice-Dammed Lake (Central Poland): 7-year cyclicity in the supply of terrigenous material

Abstract

The varved clays formed during the Saalian Glaciation (MIS 6) between Dębe and Izbica (northern Mazovia, Central Poland) were subjected to rock magnetic investigation. The studied varved clays represent a record of 110 years. In addition to annual cyclicity, there are other long-term cycles. One lasts 7 years on average and is related to changes in water level within the ice-dammed lake and/or changes in the supply of terrigenous material. This cyclicity is similar in duration to that observed in modern measurements of some parameters of the Earth’s climate system and can be influenced by the internal dynamics of the Earth. Also, the investigated clays were deposited in two sedimentation zones of the lake, distal and proximal. During the first phase of clay sedimentation connected with the distal zone, the shoreline of the ice-dammed lake was in close proximity to the stagnant ice-sheet front, and the lake deepened. The ice-sheet front was to the north of Zakroczym and Dębe and to the north of the Bug valley (Zakroczym phase). Then, the ice-sheet front retreated towards Płońsk and Nasielsk (Nasielsk phase) and a higher amount of terrigenous material was delivered, leading to the deposition of clay in the shallower, proximal zone.