Geology of the Baltic Sea

The Geology of the Baltic Sea is characterized by having both areas located at the Baltic Shield of the East European Craton and the Danish-North German-Polish Caledonides. There is a distinction between what is the current Baltic Sea depression, formed in the Cenozoic Era, and the much older sedimentary basins whose sediments are preserved in the zone. Although glacial erosion has contributed to shape the present depression, the Baltic trough is largely a depression of tectonic origin that existed long before the Quaternary glaciation.

The Baltic Sea sedimentary basin was formed on top of the East European Craton millions of years after it consolidated. This occurred during the Late Ediacaran and the Early Cambrian when the weakest part of the craton was reactivated. Since then the basin has been deepened mainly through subsidence caused by extensional tectonics. In the northern part of the Baltic Sea basin, including the Gulf of Bothnia and the Bothnian Sea, the depression originated as a series of interconnected rifts that were not active enough to split the East European Craton. Subsidence in the southern parts was most pronounced during a period starting in the Late Ordovician and lasting to Middle Silurian. At this time the Baltic sea basin and the East European Craton were part of a continent and tectonic plate known as Baltica. Baltica collided with the continent Laurentia in the Late Silurian and Early Devonian. This caused compression in the basin in a north-west to south-east direction. This collision further led to the formation of a fold and thrust belt and faults north of the Danish–North German–Polish Caledonides. During the Carboniferous and Permian the basin areas around Rügen and northern Poland were subject to the intrusion of magma. After the Permian there was little tectonic activity in the Baltic for most of the Mesozoic until the Cretaceous. During the Cretaceous a tectonic inversion occurred in the southwestern part of the basin.

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