New data on the Ladoga transgression, the Neva River formation, and agricultural development of northwestern Russia

Abstract

The geological history of Lake Ladoga, its connection with the Baltic basin, the formation of the Neva River, and the development of the whole region by people have been studied by Russian and Finnish scholars for a long time. Investigations carried out over the last fifteen years [1‐4] have made it possible to obtain new data on the problem; nevertheless, many problems still remain to be solved. To fill the existing gaps as well as to reveal the effect of hydrological changes on the early human settlements, international complex studies were carried out within an INTAS project and a project of the Russian Foundation for Basic Research. As subjects of investigation there were chosen peat bogs and lakes located in the central part of the Karelian Isthmus, in the region of the Vetokalio Rapids, the lowest area of the Ladoga‐Baltic watershed (the absolute height is 15.4 m above sea level) situated near the settlement of Veshcheevo, Vyborg raion, Leningrad oblast. Moreover, sections in the Neva River valley and in the southern part of the Ladoga region at the Volkhov and Oyat’ rivers (Fig. 1) were also studied. In the region of Veshcheevo (Karelian Isthmus), deposits of the Nizhneosinovskoe bog and Lamskoe and Makarovskoe lakes located west and east of the Vetokalio Rapids respectively were studied (Fig. 2). The section of the Nizhneosinovskoe bog located 23 m above sea level (masl) exposed the sequence of lacustrine and mire lake‐bog deposits reflecting early stages of the existence of the so-called Hejnijoki Strait: a Baltic Ice lake (BIL), the Yoldia Sea, the later stage of which was dated at 9580 ± 100 years (9200‐8600 cal BC, LY-5306), and Ancylus Lake. Judging from the data obtained, the level of the Yoldia Sea in the central part of the Karelian Isthmus (25 masl) was reached 9400 ± 130 years (9150‐8250 cal BC, LU-5309). Overlying deposits comprise the diatom assemblage characteristic of the Ancylus freshwater lake. Between 8250 and 7100 cal BC, following the regressive lowering of the Ancylus Lake level, the basin in Nizhnesinovskoe peatbog area became isolated, existed for some time as a small lake and consequently became transformed into a bog. The study of bottom deposits of Makarovskoe (11.4 masl), Lamskoe (14.5 masl), and Uzlovoe (13.0 masl) lakes revealed final episodes of the existence of the Hejnijoki Strait. Deposits represented by lake mud were formed under conditions of shallowwater, slightly running-water, and stagnant lakes. The disappearance of “Ladoga elements” from the diatom flora and a change of the sedimentary environment from the strong-flow (sandy deposits), to slow-flow and stagnant ones (organogenic deposits) perceptible after 1980 cal BC, are indicative of isolation of lakes in the course of recession of the Lake Ladoga water level.