Paleogeographic conditions of Lake formation on Andoma Ice-divide Upland

Abstract

The results of an integrated study of Late Glacial and Holocene lake-mire deposits on Andoma Ice-divide Upland, located in the Fennoscandian Crystalline Shield-Russian Plate contact zone, are reported. The geomorphological structure of the study area isdescribed. The data obtained show that it was not until the Alleröd, i. e. much later than the Late Valdai glacier had retreated from the study area, that a lake began to form in what is now a mire. This delay was due to some distinctive features of the early deglaciation stages at which dead ice blocks and massifs were formed. The stagnated ice continuedto melt until Boreal time. Terrigenous sediments accumulated in the proto-lake in Late Glacial and Preboreal time. They were rapidly succeeded by organic deposits about 7700B. P. Boreal deposits are assumed to have been completely eroded after the dead ice block damming the lake had completely thawed. As the water level of the lake declined,the lake basin began to get overgrown and peat formation continued. The plant cover development lagged much behind the glacial retreat because dead ice massifs persisted for a long time. The vegetation dynamics from Late Glacial time to the present has been reconstructed. In Late Glacial time, the study area was occupied by tundra dwarf arctic birch-true moss paleocommunities. Open birch woodland, succeeded by sparse birch forests, formed in Preboreal time. Birch forests, succeeded by birch-spruce south-taiga forests, grew in the study area in early Atlantic time. As the climate cooled down at the Atlantic-Subboreal time boundary, spruce and spruce-pine mid-taiga forests began to spread. The contribution of birch increased by the end of the Subatlantic Period.

Keywords

• spore-and-pollen analysis
• diatom analysis
• bottom sediments
• vegetation dynamics
• paleogeography
• late glacial time
• holocene
• eastern fennoscandia.