The bedrock of Sweden
The bedrock of Sweden consists of three main components: Precambrian crystalline rocks, the remains of a younger sedimentary rock cover and the Caledonides. The Precambrian rocks are part of a stable rock area known as the Baltic Shield (or Fennoscandian Shield). This consists of rocks formed during the Precambrian period, i.e. some time between the formation of the Earth about 4,600 million years ago and the start of the Cambrian period about 545 million years ago.
The oldest rocks in Sweden are Archaean, i.e. they are more than 2,500 million years old, and have been dated to between 2,800 and 2,600 million years old. Archaean rocks, however, only occur to a limited extent in the northernmost part of Sweden. The rocks in the rest of the north of Sweden and in the eastern and southern parts of the country are mostly between 2,000 and 1,650 million years old. They formed, and were in many cases also metamorphosed, in connection with the Svecokarelian orogeny. That orogeny has also affected the Archaean rocks.
The bedrock in southwestern Sweden is mainly between 1,700 and 1,550 million years old. It was metamorphosed during the Sveconorwegian orogeny, which occurred about 1,100–900 million years ago. In the south, the bedrock was also metamorphosed at an earlier stage between 1,450 and 1,400 million years ago.
Phanerozoic sedimentary rocks are resting upon the Precambrian shield area. They are less than 545 million years old and cover large parts of Skåne, the islands of Öland and Gotland, the Östgöta and Närke plains, the Västgöta mountains, the area around Lake Siljan in Dalarna and areas along the Caledonian front in northern Sweden. The youngest rocks in Sweden are Tertiary rocks, formed about 55 million years ago. They occur in the most southerly and southwestern parts of Skåne.
The Caledonian orogeny is the most recent in Sweden – it occurred about 510–400 million years ago. The rocks in the mountain chain vary in age from Precambrian to Silurian, which means that they are more than about 420 million years old.