Late Weichselian deglaciation chronology and palaeoenvironments in northern Karelia, NW Russia

Abstract

The Scandinavian Ice Sheet (SIS) was one of the largest ice sheets in Eurasia during the Weichselian glaciation. It attained its maximum extent in the east during the Late Weichselian between 18 000–15 000 years ago, covering the whole of Fennoscandia, northwestern Russia and northern Continental Europe and coalescing with the Barents Ice Sheet and the British Ice Sheet. The Weichselian deglaciation was interrupted by a sudden climate cooling episode known as the Younger Dryas Stadial (ca. 12 800–11 500 years ago). This thesis examines the palaeoenvironments in front of the SIS during the Late Weichselian and Early Holocene (ca. 12 500–11 000 years ago). The eastern and western Rukajärvi, Kalevala and Pääjärvi end moraines were dated in order to reconstruct the position of the ice margin in Russian Karelia during the last deglaciation.

A number of palaeoenvironmental research techniques were used. Morphologically different land systems in the field were examined by glacial geomorphological studies and in aerial photos and satellite images. Internal structures of glaciofluvial formations, especially delta plains and beach deposits, were studied using ground penetrating radar (GPR). These flat plains were used as elevation data to produce distance diagrams for GIS-based reconstruction of the White Sea Basin water levels in the Younger Dryas Stadial. Early development of the White Sea was also studied, using conventional shoreline displacement methods. Finally, deglaciation chronology of the study area was determined using a combination of glacial varve chronology and palaeomagnetic dating of three lacustrine sediment sequences from basins situated in the end moraine zones. Geomorphology, ¹⁴C AMS dating and previous knowledge of ice lobe retreat rates were also used for chronological analysis.

The results indicate that the Kuusamo-White Sea and Northern Karelian ice lobes of the SIS operated in the area and deposited several fan-shaped geomorphological landform patterns and end moraine zones. Indications were found that four ice advances occurred in the area during the Late Weichselian and Early Holocene deglaciation. The eastern arc of the Rukajärvi end moraine, in the Rukajärvi-Belomorsk area, marks the southernmost limit of the Kuusamo-White Sea ice lobe advance, the oldest in the area. The Onega sub-ice lobe (part of the Kuusamo-White Sea ice lobe) apparently advanced from the north-northwest to the eastern Rukajärvi end moraine zone, which was deposited ca. 12 500–12 300 years ago. As deglaciation continued, the northern Karelian ice lobe was formed and advanced from west to east, depositing the western arc of the Rukajärvi end moraine 11 700–11 600 years ago.

The North Karelian ice lobe retreated westward but advanced again and the Kalevala end moraine was deposited in front of the ice margin 11 400–11 300 years ago. Further north, the Pääjärvi end moraine was accumulated at the margin of the Kuusamo-White Sea ice lobe 11 000 years ago. There were indications that the western Rukajärvi end moraine was correlated in time with the Salpausselkä II in southeastern Finland, while the Kalevala end moraine was possibly deposited as the same time as Salpausselkä III in southwestern Finland.

The results also suggest that the Kuusamo-White Sea ice lobe terminated in a glacial lake that occupied the White Sea Basin and adjacent land areas. Around 12 050 years ago the waters of this ice lake burst into the Barents Sea via the Gorlo Strait and the lake water level fell by approximately 50–60 metres within 200 years. After this event the White Sea Basin was connected to the Barents Sea. The northern parts of the Kuittijärvi and Tuoppajärvi sub-ice lobes terminated in shallow water.

Keywords (GeoRef Thesaurus, AGI): glacial geology, Scandinavian ice sheet, deglaciation, ice-marginal features, end moraines, chronology, paleoenvironment, glacial lakes, Weichselian, Younger Dryas, Russian Federation, Republic of Karelia, Kalevala, Belomorsk, White Sea

Niko Putkinen
Geological Survey of Finland, P.O. Box 96, FI-67101 Kokkola, Finland

E-mail: niko.putkinen gtk.fi