Asynchronous development of two Late Glacial lake basins near the Drwęca ice-marginal valley (N Poland)

Lacustrine organic sediments were sampled at Gronowo (Chełmno Plateau) and Piotrkowo (Dobrzyń Plateau) located within a widespread system of subglacial channels separated by the large Drwęca ice-marginal valley. They have been examined for their pollen, plant macro-remains and geochemistry, as well as radiocarbon-dated. The analyses have allowed reconstructing the evolution of the area and presenting an asynchronous appearance of two lakes. Before lake sedimentation, glaciolimnic sediments from the end of Plenivistulian, at the site of Piotrkowo, was dated. Lacustrine sedimentation started during the Allerød at Gronowo, and during the Preboreal at Piotrkowo. The different age of the two lakes is ascribed mainly to differences in the Late Glacial drainage conditions which directly affected the melting away of dead-ice blocks buried in the channels.