Geology of the Baltic Sea

Historical geologists make a distinction between the current Baltic Sea depression, formed in the Cenozoic era, and the much older sedimentary basins whose sediments are preserved in the zone.

[1] The Baltic Sea sedimentary basin was formed on top of the East European Craton millions of years after it consolidated.

At this time the Baltic sea basin and the East European Craton were part of a continent and tectonic plate known as Baltica.

[1] The oldest sedimentary rocks in the Baltic Sea area that are not metamorphosed are Jotnian orthoquartzite, siltstones and conglomerates.

[5] Glacial erosion has superficially scoured an elongated area of the Baltic spanning from northern Småland, via Stockholm and Åland to the coast at the Finnish-Russian border.

[6] The scoured area and other zones made up of crystalline Fennoscandian Shield rocks (northern and western Baltic Sea) have experienced overall very limited glacial erosion during the Quaternary.

[9] Important to the understanding of the Baltic basin during the Quaternary was its connection to the open ocean in the west through the area of Denmark and Scania.

[9] When the last ice sheet began to retreat north from the Baltic Sea depression in the early Holocene (ca.

Eventually mixing and connection to the ocean did occur when the glacier front retreated to the north beyond Billingen about 11,500 years ago.

About 10,700 years ago the continued land rise separated the Baltic water body from the ocean again and Yoldia Sea turned into the Ancylus Lake.

This lake lasted until 10,000 years before present when a new connection to the ocean was established, this time in the Danish straits forming the Littorina Sea.