Matti Eronen

Maankohoamisen, rannansiirtymisen ja Itämeren vaiheiden tutkiminen suo- ja järvikerrostumien perusteella

Eronen M. Maankohoamisen, rannansiirtymisen ja Itämeren vaiheiden tutkiminen suo- ja järvikerrostumien perusteella.

Tiivistelmä

The first part of the study is concerned with some general aspects of the various stages of the Baltic Sea, land uplift and shore-line displacement during the period following the last glacial period. Land uplift was much faster immediately after the end of the glacial period than it is today. As a result of land uplift, regressive shoreline displacement, i.e. movement of the shore-line seawards, has prevailed along the coast of Finland during the time following the glacial period. However, in SE Finland the sea has risen during two separate periods, at a faster rate than the rate of land emergence, and so land which has earlier emerged from the sea has again been covered, i.e. transgression has taken place. The Ancylus transgression occured around 9500—9000 B.P. and was caused by the damming up of the water in the Baltic Sea basin at a level above that of the sea during the Ancylus Lake stage. Towards the end of the Ancylus Lake stage rapid regression took place as the surface of the lake subsided to the level of the Atlantic Ocean. Regression changed to transgression after the surface of the ocean had risen, due to the so-called eustatic rise, above the threshold level of the Straits of Denmark. The eustatic rise caused by melting of the glaciers produced a considerable amount of transgression in the Baltic Sea basin during the warm period which started in the Mastogloia stage and continued into the first half of the Litorina Sea stage. At the start of the Litorina Sea stage, between 7500—7000 B.P., the water in the Baltic Sea basin clearly became salty brackish water. The transgression which occured during the Litorina Sea stage extended from the coast of SW Finland as far as the Helsinki—Espoo area. Further west, however, land uplift occured at such a fast rate that shore-line movement throughout the warm period was regressive. In the latter half of the paper, a number of examples have been presented to show, how the various phenomena connected with the development phases of the Baltic Sea and shore-line movement can be seen in the peatland and lake-sediment layers. Examples of peat layers showing transgression are to be found in Hangassuo swamp, near Anjalankoski (Eronen 1976) and Bastuberg swamp, near Porvoo (Eronen 1974). The peat layer covered by the Ancylus transgression is visible in the peat profile from the former swamp. On the other hand, the sediment layer of a small lake is covered by the Litorina transgression in the Bastuberg swamp. In addition to these, a number of examples have been presented of transgression sediment layers produced by the large lakes of the Finnish Lake District. After contracting from the Baltic Sea basin, the water in the Finnish Lake District flowed towards the Gulf of Bothnia. However tilting of the lake basins caused by land uplift of varying degree resulted in transgression, especially in the southern and south-eastern parts of large lakes. Transgression of Lake Päijänne can be seen in layer series from Lahnalampi (Asikkala) (Saarnisto 1971). Transgression of Lake Saimaa has been demonstrated in bottom layer sediments from Puntusensuo (Kerimäki) (Saarnisto 1970). Transgression ceased in both of these large lakes after a new discharge channel had formed. The water from Lake Päijänne started to flow southwards in about 6000 B.P. and the water from Lake Saimaa broke through Salpausselkä II in about 5000 B.P. forming River Vuoksi.

Vastaanotettu 31.10.2017 Julkaistu 1.1.1976

Katselukerrat 1139

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