2. Geological Evolution and Resources of the Baltic Sea Area from the Precambrian to the Quaternary

The Baltic Sea is a young geomorphologic feature that formed during Quaternary time. It covers the western and the central part of the Baltic sedimentary basin. The origin of the Baltic Sea and of the corresponding morphological low is still controversial, considered by some as an erosional structure and as a tectonic depression by others. The chapter gives a summary of the evolution and the known resources of the Baltic sedimentary basin focussing on its central part and thus tries to present new evidence for the origin of the Baltic Sea. The Baltic sedimentary basin was formed during Late Ediacaran–Early Cambrian time. Its formation was caused by the reactivation of the weakest lithospheric part of the East European craton. All the following stages of pronounced basin subsidence (major subsidence phase during Late Ordovician–Middle Silurian), including the recent tectonic stage, were dominated by extensional tectonics. However, the most intense structuring of the crust in the region took place in a compressional setting during Late Silurian and Early Devonian time. The NW–SE-directed compression was caused by the collision of Laurentia and Baltica. It caused the formation of an Early Palaeozoic thrust and fold belt at the margin of the East European craton and led to the formation of E–W and NE–SW striking faults in the Baltic basin northeast of the Danish–North German–Polish Caledonides during that time. Typical for the Permocarboniferous period are magmatic intrusions in the southern part of the Baltic Sea, in northern Poland, and in the area of the Rügen Island. Tectonic activities ceased within the Permian and only small amplitude faulting is detected in the Mesozoic. Later on, tectonic activities increased during the Cretaceous inversion in the southwestern part of the basin. The typical wrench-dominated faulting is related to the reactivation of Pre-Permian fault systems by Late Cretaceous inversions of the Mesozoic Danish and Polish basins. Large-scale ancient structures of the Baltic basin are reflected in the sea bottom morphology. Detailed analysis indicates that those morphological structures are mainly passive features related to selective glacial erosion, but some hints for neotectonic activities do also exist. Glacial erosional processes undoubtedly contributed to the shape and depth of the Baltic Sea. Evidences available today, however, suggest the existence of a pre-existing tectonic depression. Major resources of the deeper underground of the Baltic basin are oil, gas, geothermal energy and reservoir formations which can be used as storage sites (natural gas, CO₂, compressed air). Location of known oil and gas fields shows a strong relation to the major fault zones.