Weichselian in Finland before 15,000 B. P.

120

An active search for pre‐Holocene organic deposits in stratigraphically well‐defined positions has proved to be a useful tool for reconstruction of glacial and non‐glacial Weichselian development in northernmost Sweden. The investigations have been concentrated to kettle holes connected to eskers belonging to a morphologically prominent northwesterly glacial system characterized by extensive drumlinization. Organic deposits, radiocarbon‐dated as older than the Holocene, have been found at some 25 localities. Some sites display two organic‐bearing sequences separated by a till bed. The pollen flora in the lowest organic bed reflects an interstadial vegetational development: Arctic shrub and herb tundra‐subarctic light birch forestherb tundra with ericaceous shrubs and dwarf birch. This interstadial is correlated with Peräpohjola in Finland. During the younger Tärendö Interstadial the vegetational development was similar, but a more continental climate is indicated hy high values of steppe plants, e.g. Artemisia and Chenopodiaceae. The Tärendö Interstadial, correlated with Odderade, wascharacterized by open, unstable soils due to periglacial processes such as cryoturbation and eolian activities. The Weichselian glaciation is divided into three glacial stades separated by ice‐free interstadials in the area studied. Except for a zone with S‐SW drumlinization the impact of the two later ice sheets is insignificant.

Section: Znferred Deuelopment F R O M Present Investigationsmentioning

confidence: 99%

“…No organic sediments have been found between the tills and the sand and gravel are assumed to date from the latest deglaciation, and attributed to oscillations of the ice margin (e.g. Hirvas et al 1981;Hirvas & Nenonen 1987).…”

Section: Znferred Deuelopment F R O M Present Investigationsmentioning

confidence: 99%

Kettle holes ‐ stratigraphical archives for Weichselian geology and palaeoenvironment in northernmost Sweden

Lagerbäck

Robertsson

1988

120

“…The deposits interpreted as interstadial in origin, on the other hand, differ markedly from the interglacial ones, although they all bear a close resemblance one to another, so that they may well represent the same phase, the Perapohjola Interstadial, as designated by Korpela (1969). This identification of only one interstadial in the Weichselian, together with lithostratigraphical evidence, has led to a relatively simple binary division of the Weichselian in Finland, in which the Perapohjola Interstadial splits the glaciation into two parts, each represented by one or two till beds (Hirvas et al 1981).…”

Section: Discussionmentioning

confidence: 99%

“…A considerable amount of research into glacial geology has been carried out in Finland, mainly within the last ten years, with the aim of determining the till stratigraphy of given sites, and in the course of this and other work numerous instances of interglacial or interstadial deposits buried beneath till have been discovered, although only a few of these cases have been investigated as yet (Korpela 1969;Hirvas et al 1981;Forsstrom 1982;Aalto et al 1983;Donner 1983). Altogether a fairly large amount of stratigraphical material has accumulated, but even the basic division of the Quaternary in Finland is still a matter of controversy, and there are many questions on which fundamental differences of opinion exist.…”

mentioning

confidence: 99%

Eemian and Weichselian correlation problems in Finland

Forsström

1984

The Quaternary stratigraphy in Finland is discussed on the basis of an example from the Oulainen area of Ostrobothnia. Organogenic deposits found beneath till at this site are correlated with the Eemian Interglacial on biostratigraphical evidence. This is confirmed by TL dates of 97,000 ± 18,000 B.P. and 150,000 ± 30,000 B.P., whereas a finite radiocarbon date of 63,200 +5500 ‐3200 B.P. is probably too young. Correlation of the Weichselian stratigraphy is based on deep‐sea oxygen isotope data, in which the variations in isotope ratios are assumed to reflect global changes in climate and fluctuations in the volume of the ice‐caps. It is concluded on the latter grounds that Finland must have been free of ice at two periods during the Early Weichselian but at least for the most part covered by ice thereafter up to the final deglaciation. The sediments attributed to the only known Weichselian interstadial in Finland, the Perapohjola Interstadial, are taken to correspond most probably to the Brørup, although some may represent the Odderade, Information on the Weichselian till stratigraphy in the Oulainen area is largely confined to the deglaciation phase, the relatively complex nature of which suggests that complete reconstruction of the earlier phases of the Weichselian in an area such as Finland, located towards the centre of the ice sheet, is scarcely feasible by the methods currently available.

“…In northern Finland several sites with tillcovered peat and gyttja beds have been described and are considered to represent the Eemian Interglacial (Hirvas et al 1981;Hirvas 1983;Donner et al 1986). The tree pollen spectra in these deposits are predominated by Pinus and Betula, mixed with Picea and Alnus.…”

Section: )mentioning

confidence: 99%

A Late Pleistocene sequence at Seitevare, Swedish Lapland

Robertsson

Rodhe

1988

A peat layer beneath two till beds was found at Seitevare in Swedish Lapland. The pollen flora layer indicatesdeposition duringthe later part of the Eemian Interglacial. Thevegetation consisted of open forests predominated by pine and birch, mixed with alder and spruce. The sedimentation took place in a small oligotrophic-dystrophicwaterbasinwithapHabout5,accordingtothediatomflora. Inanadjacentsection, silty sediments with pollen indicating interstadial vegetation (birches, herbs) are covered by one till bed. These sediments are tentatively correlated with the Perapohjola Interstadial in northern Finland and northeastern Sweden. The lithostratigraphy indicates one pre-Eemian and probably three Weichselian glacial advances.