Geological evolution of the Baltic Artesian Basin

The Baltic Artesian Basin (BAB) is one of the largest groundwater basins in Europe. It is spread over the Palaeozoic Baltic sedimentary basin and the whole territory of Estonia, Latvia, Lithuania and the Kaliningrad region of Russia, part of the Leningrad and Pskov regions of Russia, Belarus and the north-eastern part of Poland, as well as wide areas of the Baltic Sea, including Gotland Island. Its total
area is 462,000 square kilometres: about 255,000 – 260,000 square kilometres being the land area with the remaining part being under the waters of the Baltic Sea.
The BAB covers a vast region that spreads across the north-western part of the core of Eastern Europe and the East European Craton (EEC). The area of the EEC formed when several small continents and island arcs collided and joined together about two billion years ago during the Paleoproterozoic. Precambrian metamorphic and igneous rocks now form the stable basement of the BAB. The entire
region has a low relief, reflecting more than 600 million years of relative tectonic stability. During the long and complicated geological history, several regional tectonic elements formed within the area of the BAB such as the Baltic Syneclise, the Latvian Saddle, the southern slope of the Baltic (=Fennoscandian) Shield, and the Mazurian-Belarussian Anteclise, which is characteristic of the Cambrian – Carboniferous time. The Middle Baltic Depression and the Polish-Lithuanian Depression, formed later as well within the southern part of the Baltic Syneclise (Brangulis and Kaņevs, 2002). Throughout the Phanerozoic, the mostly low-lying territory of the Baltic States remained relatively weakly affected by the mountain-building tectonic collisions suffered by the western, northern and eastern margins of the EEC. An exception is the Caledonian Orogeny during the late Silurian – Early Devonian. After this the territory of the BAB continuously received deposits from the eroding Caledonian Mountains throughout the Devonian and Early Carboniferous. Sediments eroding from the Caledonian Mountains to the northwest washed into the sea and were deposited as layered wedges of fine debris. As sand, carbonate mud, and clays accumulated, the Devonian Baltic Basin was filled and retreated south-westward.
During most of the Mesozoic Era, the territory occupied by the BAB was mainly slightly above sea level, with the exception of the Polish-Lithuanian Depression (Paškevičius, 1997), and the Jurassic when the rising seas flooded the lowlying areas of the continent. Younger, Cretaceous and Neogene deposits are distributed in a relatively smaller part of the BAB. The whole territory of the BAB was significantly affected by several glaciations during the Quaternary.