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Observations on the Quaternary geology of an area between the 2nd Salpausselkä and the ice-marginal formation of central Finland

1971; Geological Society of Finland; Volume: 43; Issue: 2 Linguagem: Inglês

10.17741/bgsf/43.2.005

1799-4632

R. Repo, R. Tynni,

Geological formations and processes

The present study deals with the Quaternary formations and especially with the drumlins in the area between the Salpausselkä system in eastern Finland and the marginal formation of central Finland (Jyväskylä).Early late-glacial sediments from the area have been dated by C 14 and pollen analyses.The Pieksämäki-Juva region is strongly drumlinized.According to seismic refraction data, the average thickness of the till forming a drumlin in Pieksämäki is about 20 meters.The drumlins in Joroinen are mostly low and narrow.According to seismic data, the till is also much thinner, averaging only 7 meters.The drumlins in the study area were formed, according to the authors, at a very late stage of the glaciation in the wide marginal region of a thinning glacier terminating in fairly shallow water.The weak glaciofluvial activity of the glacier could also have been a factor contributing to that formation, although in the final stage, it has been a question of the reactivation of the ice-flow.The most important of the presented sediment profiles from bogs is the stratigraphic section from the Vuorilampi-pond in Jyväskylä.It is located west of the proximal part of the marginal formation.The C 14 -age of the oldest dateable sediments from this area was 8 130 ± 160 B.C.According to pollen statistics, it corresponds to the beginning of the Preboreal or the end of the Younger Dryas period.Due to the possibility of having interglacial organic matter in the sample, the validity of the dating should be accepted with some reservation.It is, however, supported by the C 14 -dating made by Salmi (1962) from the oldest organic sediments of the Lapaneva bog in Kihniö, west of Jyväskylä.