DEGLACIATION IN EASTERN AND CENTRAL ... - arkisto.gsf.fi

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Thus Salpausselkä Salpausselkä I marks marks the limit of a number number of glacigenic phenomena. phenomena. The
sequence of glacigenic glacigenic deposits is much more complex on the proximal proximal than on the
distal side of ofthe the formation. formation. The till separates separates two sequences of ofdeglaciation deglaciation deposits
of different age. The network network of glacial streams does not clearly continue through
Salpausselkä Salpausselkä I, and the set of of striae striae on its proximal proximal side frequently frequently differs from that
on its distal side. The uppermost uppermost till is rather immature, immature, and thus the original
sediments can still be identified. identifred. These phenomena are most most obvious in an area
extending extending from Salpausselkä Salpausselkä I to about 20 km on the proximal proximal side of Salpausselkä
11, II, i.e. for 40-45 km. Farther away away they they are less less numerous, numerous, but till-covered
sediments are still found 70-80 km km or more from from Salpausselkä I. During the Heinola
deglaciation the ice sheet sheet seems seems to have receded receded to at least least 80 km north of
Salpausselkä Salpausselkä I, to a line extending extending from from Koli Koli to to Turku T\rrku via via Viinijärvi, Heinävesi,
Rantasalmi, Rantasalmi, Mikkeli, Kuhmoinen, Kuhmoinen, Toijala Toijala and Loimaa. Loimaa.
Certain factors, however, argue against against the idea idea presented above. There is nothing
in the varve chronology chronolory to corroborate the Heinola deglaciation (Niemelä (Niemelä 1971). The
base level of erosion shown by the the till-covered glaciofluvial deposits is incompatible
with what is known known of late-glacial late-glacial development on the distal side of Salpausselkä I.
Many Many phenomena could also be be explained explained by several short oscillations of the ice
margin. margin.
It is pointed out that that neither neither the the clay clay chronology of Niemelä Niemelä nor the earlier
chronology chronology of ofSauramo Sauramo support support the concept concept of ofsubstantial substantial oscillation. The high base
level of of erosion indicated indicated by the till-covered till-covered glaciofluvial deposits was found to be
incompatible incompatible with the fact that the g level, which is is markedly markedly lower than the B level
and is interpreted as the base level level of of erosion in the distal area of Salpausselkä I,
should also have existed existed in the north of Salpausselkä Salpausselkä I I during the Heinola
deglaciation.
deglaciation.
III
Rainio, H., Kejonen, .&, Kielosto, S. & Lahermo, P. 1986.
Avancerade inlandsisen pä pa nytt ocksä ocksa till till Mellanlinska
Mellanfinska
III Rainio, H., Kejonen, A., Kielosto, S. & Lahermo, P. 1986.
randformationen? Summary: Is the Central Finland ice-marginal
formation formation terminal? terminal? Geologi 38 (4-5), 95-109.
Although generally considered a recessional formation, the Central Finland icemarginal
formation - the fourth fourth large chain of ice-marginal ice-marginal formations in southern southem
Finland - has has also been regarded as a a formation deposited in front front of an ice sheet
that had readvanced readvanced for a few kilometres. This latter concept is based on the
presence of a few till-covered glacial glacial deposits on the proximal proximal side of the formation.
It has also been suggested that that the Central Central Finland Finland ice-marginal ice-marginal formation is a
diachronous diachronous formation or that it deposited in a wide crevasse in the ice or in a large
glacial bay or even even that it is an interlobate interlobate deposit.