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Herein lie the "Lost" Boreas Files by Rockessence

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Author Topic: Herein lie the "Lost" Boreas Files by Rockessence  (Read 7522 times)
Janna Britton
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« Reply #135 on: November 16, 2008, 03:36:47 am »

Riven
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  posted 01-17-2005 16:31             
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Late Weichselian and Holocene shore displacement history of the Baltic Sea in Finland
MATTI TIKKANEN AND JUHA OKSANEN
Tikkanen, Matti & Juha Oksanen (2002). Late Weichselian and Holocene shore displacement history of the Baltic Sea in Finland. Fennia 180: 1-2, pp. 000-000. Helsinki. ISSN 0015-0010.
http://www.helsinki.fi/maantiede/geofi/fennia/demo/pages/oksanen.htm

About 62 percent of Finland's current surface area has been covered by the waters of the Baltic basin at some stage. The highest shorelines are located at a present altitude of about 220 metres above sea level in the north and 100 metres above sea level in the south-east.

Around 10,300 BP this ice lake discharged through a number of channels that opened up in central Sweden until it reached the ocean level, marking the beginning of the mildly saline Yoldia Sea stage (10,300-9500 BP). As the connecting channels rose above sea level, however, the Baltic Sea became confined once more, to form the Ancylus Lake (9500-8000 BP).

The ice sheet associated with the Weichselian glaciation, which followed the Eemian interglacial, reached its maximum extent about 18,000-20,000 BP. It was more than three kilometres thick in the area of Finland, so that it depressed the earth's crust to such a degree that a considerable part of the country's present area lay beneath the waters of the Baltic basin immediately after deglaciation. As the burden of the overlying ice was released the crust began to rise rapidly, however, so that it is estimated that the total rise up to the present time has been 600-700 metres on the northern coast of the Gulf of Bothnia, 400-500 metres in the middle part of Finland and in central Lapland, and around 300 metres on the coast of the Gulf of Finland and in northern Lapland (Mörner 1980). The majority of this rise nevertheless took place as the ice was melting, before the ground surface became exposed.


Then, around 11,200 BP, a (possibly subglacial) connection to the west opened up north of Mount Billingen in central Sweden. This remained functional for some 400 years, and allowed the water level in the Baltic to return to that of the outside ocean, presumably implying a decline of 5-10 metres

By the time the Younger Dryas cold phase came to an end, the Second Salpausselkä marginal formation was also in existence, and the sharp warming of the climate around 10,500 BP then caused the ice margin to retreat rapidly (Björck 1995). As a consequence, the Billingen 'gateway' opened up again around 10,300 BP and the waters of the Baltic Ice Lake once more began to discharge into the ocean through central Sweden (Fig. 2B). This dropped the water level in the Baltic basin by 25-28 metres within a few years, regaining the level of the outside ocean.

As the ice margin retreated further, the Närke Strait in the lowlands of central Sweden north of Billingen opened up about 10,000 BP, allowing saline water from the ocean to flow into the Baltic basin (Eronen 1990; Björck 1995)

Ocean levels rose at a rate of more than a metre per century around 10,000 BP, but the water level was still 30 metres below what it is today (Taipale & Saarnisto 1991: 237)

This marked the beginning of the Ancylus transgression, which lasted about 300 years (9500-9200 BP). During this time, the rising water level caused extensive areas of land to be inundated once more, especially on the south coast of the Baltic, where practically no land uplift took place. The water was rising at a rate of 5-10 centimetres a year, and the transgression as a whole is estimated to have been of the order of 15-25 metres (Eronen 1990; Björck 1995).

The rising waters of the Ancylus Lake eventually exceeded the threshold known as the Darss Sill in the south-western part of the Baltic basin and water began to flow out through the Dana River, at the site of the present-day Great Belt (Store Bælt), around 9200 BP (Fig. 2E). This brought the Ancylus transgression to a close and severed the land connection between Sweden and Denmark at the same time. For a time the channels across central Sweden functioned alongside the Dana River, but the rapid regression of the Ancylus Lake, combined with land uplift, soon caused these channels to dry up (Björck 1995).


 
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