New data on the palaeo–incisions network of the south–eastern Baltic Sea

Abstract

The present study area is located within the south–eastern segment of the Baltic Sea framed by 55o30’–56o30’ N and 19o00’–21o15’E. The area is re-visited with the aim to describe in more detail the geologic prerequisite and development of the palaeo–incisions as well as the timing of their subsequent infillings. The channels form distinctive features in the sedimentary bedrock along the outer limits of pre–Weichselian ice sheets, on average reaching depths into the bedrock of 50 m in the nearshore zone of Lithuania to 100 m along the slope to the Gotland depression in the west. The development of palaeo–incisions systems is governed by the easily eroded late Palaeozoic to Mesozoic bedrock of the present area. Only rare ocurrences of channels have been reported from the middle and lower parts of the Palaeozoic further west in the Baltic Sea. The present investigation supports a mechanism that the channels formed below the ice near the ice sheet margin by melt water erosion under high pressure. The channels start at random where a fracture in the ice develops forming outlet of water contained below the central part of the ice sheet. The channels often merge together in the direction of the ice margin, possibly gradually adapting to previous fracture systems in the bedrock. The investigated incisions were infilled prior to the advance of the Weichselian ice sheet and some have been reopened and repeatedly infilled.