Sedimentation and lithostratigraphy of the Vuosaari multiple till sequence in Helsinki, southern Finland

Abstract

A multiple till sequence interbedded with sorted sediments has been investigated at Vuosaari, Helsinki, Finland. The investigation was carried out using standard sedimentological procedures combined with microfossil analysis in order to determine the genesis of the exposed sediments. This evidence is used to correlate lithostratigraphically the sequence with adjacent multiple till sequences in other parts of southern Finland (south of the Salpausselkä zone).It is concluded that all three till beds at Vuosaari are of basal origin that were laid down by separate ice flow phases. In contrast two rhythmite beds between the tills are thought to have been deposited in open water. The sediments at Vuosaari may have been laid down during the Weichselian glaciation although it is also possible that the lowermost till bed represents Saalian till.

Weichselian sediment succession at Ruunaa, Finland, indicating a Mid‐Weichselian ice‐free interval in eastern Fennoscandia

“…35–25 kyr ago (Nenonen 1995; Ukkonen et al 1999; Lunkka et al 2001). Our results from the Ruunaa area suggest that the first ice advance into eastern Finland took place in the early Middle Weichselian, when eastern Lapland and southeastern Finland were also covered by ice (Hirvas et al 1995; Helmens et al 2000, 2007).…”

Lithostratigraphy of Late Weichselian tills on the West Estonian Islands

“…between SSI and the Palivere endmoraine) two (Hirvas & Nenonen 1987, Bouchard et al 1990, Salonen & Glückert 1992, Saarnisto & Salonen 1995 or three (Hirvas et al 1995) till units are distinguished. Because the superficial bedrock composition in Finland and Estonia are completely different, a strictly lithostratigraphic correlation of till units across the Gulf of Finland is not possible.…”

“…However, it should be remembered that the approximate timing of stadial/interstadial episodes in SW Finland are chronostrati- graphically not controlled (e.g. Hirvas & Nenonen 1987, Salonen & Glückert 1992, Hirvas et al 1995 and only indirectly determined in NW Estonia (see Pirrus & Raukas 1969, Raukas 1992a, Hang 1997. Nevertheless, the Espoo Till of Bouchard et al (1990) and Salonen and Glückert (1992), or till unit 6 of Hirvas et al (1995) may correlate to the Palivere Till in NW Estonia as both are topmost, youngest and similar age till units in the area between the SSI and Palivere endmoraines (Table 2).…”

“…The Siuntio Till in SW Finland is time-correlative to the Oldest and Older Dryas stadials (Salonen & Glückert 1992) and thus may be roughly correlated to the Pandivere or older late-glacial tills in Estonia (Table 2). Later, in the Vuosaari section Hirvas et al (1995) considered the Siuntio Till (unit 4 in Vuosaari) to be of Middle Weichselian age and described an additional till below it, possibly deposited during the Saalian glaciation. As stated above, it is not possible at present to estimate the stratigraphic position of the pre-Pandivere till on the Sörve Peninsula and to draw correlations to the distinguished till units in SW Finland.…”

The SE sector of the Middle Weichselian Eurasian Ice Sheet was much smaller than assumed

“…There is no conclusive evidence for a Middle Weichselian till at stratigraphically different sites in the S Finland, as the proposed Middle Weichselian tills at Ruunaa and Vuosaari (Hirvas et al, 1995) can just as well be Saalian in age. Our paleoenvironmental scenario with one single Late Weichselian glaciation in the SE sector of the EIS is supported by the fact that several in situ Eemian deposits recorded in S Finland are covered by one single till bed (Nenonen, 1986;Peltoniemi et al, 1989).…”