The Ancylus Lake stage in the sediment records of its easternmost fringe

Abstract

The Ancylus Lake stage is the Early-Holocene stage of the evolution of the Baltic Sea when isostasy-driven termination of the connection between the Baltic and Ocean resulted in a formation of a large transgressive freshwater lake in the Baltic basin. During this period, the coastal lowlands of the present Gulf of Finland were flooded, while Lake Ladoga, the largest lake in Europe, was connected to the Ancylus basin through a strait in the northern part of the Karelian Isthmus. Despite the long history of studying the sediments of Lake Ladoga a number of questions concerning the early stage of the Ladoga evolution remain unresolved. Those include the detection of the sediments of the Ancylus stage, specifying the area, configuration and depths of the water body that existed during this period in the Ladoga basin. To reveal signals of the Ancylus stage, sediment cores retrieved from the open-water part of Lake Ladoga and small lakes in the northern part of the Karelian Isthmus were studied. Diatom study of the Ladoga sediment cores revealed the presence of characteristic Ancylus species in the composition of diatom assemblages. However, their presence not only in the sediments of the Ancylus time but also during the entire Early Holocene, limits their indicative potential for identifying signals of the Ancylus transgression in Lake Ladoga. High percentages of benthic diatoms is thought to be more informative for reconstructing environmental and lake-level changes in Lake Ladoga in the Early Holocene. High amounts of the indicative Ancylus species recorded in the Early-Holocene sediments of small lakes in the northern part of the Karelian Isthmus suggest the formation of the diatom assemblages within the same basin, which evidences for the penetration of the waters of the Ancylus Lake into the Ladoga basin.

Keywords:

diatoms, Ancylus transgression, Lake Ladoga, Early Holocene, lake sediments