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Agnes M. Raaness

Forsker
Phone: 73904317
Anette Granseth's picture

Anette Granseth

Forsker
Phone: 73904324

Geological fun facts following the World Tour race Tour of Scandinavia 2022

Black stone with purple colour. A hammer is in the right corner.
Here you see a cobolt mineral you`ll learn more about under Stage 5. Photo: Jan Sverre Sandstad, NGU.
The race from 9 to 14 August offers a lot of geological fun facts.

You can read more about the race at the Tour of Scandinavia webpage.

The geological framework of #TourofScandinavia is the Precambrian basement which were originally sediments and volcanic deposits deposited app. 1500 to 1040 million years ago. The Precambrian evolution of Southwestern part of Scandinavia culminated with the formation of the Sveconorwegian Mountain Chain app. 1130-900 million years ago, both deforming, folding and metamorphosing the majority of these rocks. However, a few granitic batholiths which intruded the crust escaped this deformation. This mountain chain is long gone, but its legacy still affects the landforms, soil, vegetation, and settlement patterns.

The cyclist follows a route through the southwestern Scandinavian basement, as well as the glacial terrains of Zealand and the root of the skerries in SW Sweden. We hope you enjoy the geology as well. 

Denmark. Stage 1, 9 Aug

An extreme close-up of chalk which looks like round and square black/grey shapes.

An extreme close-up of chalk. Photo: B. Willemoes-Wissing, NGU.   

The first stage of the Tour of Scandinavia will take place in the north-eastern part of Zealand in Denmark. Anyone who has been biking in Denmark knows that the landscape is not flat but undulating.

It has been shaped by several glacial, glacifluvial and postglacial processes. The soils are the remains of the Scandinavian highlands being grinded off by glaciers and related process and then deposited on top of calcareous marine sediments that was deposited on top of the SW Scandinavian basement.

The marine sediments are chalk, limestone and clay, deposited millions of years ago, and several layers also contain fossils.

A path with green forest near a lake.

Zealand in Danmark. Photo: Terje Bjerkgård, NGU. 

Sweden. Stage 2, 10 Aug

A seagull stands on top of a brown rock in the sea. Some square stones in the background.

Probably it is left overs from one of Hvalers many stone quarrys of Iddefjord granite which the seagull guards. You`ll learn more about the Iddefjord granite in the next stage. Photo: Rolv Magne Dahl, NGU. 

A closer look at some stones which is probably Iddefjord granite. Photo: Rolv Dahl, NGU. 

Geologywise, the second stage is an appetizer of the 3rd,4th and 6th stage of this tour. The main bedrock are Precambrian gneisses (1590-1660 Ma), but also some of the youngest rocks of the Scandinavian basement, the Bohus (S) or Iddefjord (N) granite. (app. 900 Ma.o.).

The most famous feature of the southwestern part of Sweden is the pittoresque coastline, small islands and rounded hills. The base for this landscape was made several hundred million years ago. Even before the dinosaurs lived on Earth, the failed rifting of the Oslo rift caused formation and exposures of faults and weakness sones. Due to continental drifting, the early Scandinavians lived in a tropical zone, perfect for deep weathering – particularly on the weakness sones.

Skipping forward in time, the continent moved northwards, and glaciers and their relatives removed both meters of bedrock and younger particles deposited on top of it. However, the weakness zones remain by affecting the topography, causing rounded hills at the mainland and skerries to pop up from the sea.

Norway. Stage 3, 11 Aug

A staue of a man holding a womans head. In the background there is a statue of naked bodies forming a tower.

It`s used Iddefjord granite in the Monolith. Photo: Tom Heldal, NGU. 

Stage 3 starts in a hot magma chamber several kilometres deep down in the crust. If this had been a bike race taking place 925 million years ago, the heat would be overwhelming, and the bikes would melt in the molten magma.  The magma intruded the surrounding metasedimentary gneisses 925 million years ago and became what is known as the Iddefjord granite in Norway and Bohus granite in Sweden.

The granite is particularly known for its good properties for use as natural stones and building blocks, and it is possible to find it in large cities around the world. However, one of the most famous and spectacular uses of the Iddefjord granite is the large sculpture “the Monolith” by G. Vigeland, the center piece of the Vigeland installation in Frogner Park in Oslo.

The Monolith was made from one single piece of granite, weighing 270 tons, and it represents the largest single piece of rock extruded in Norway.

Norway. Stage 4, 12 Aug

Stones that looks like potatos.

Orbicular norite. Photo: Jan Sverre Sandstad, NGU.

The 4th stage is a geological rarity.

The «potato rock deposit» at Romsåsen in Askim, is a true geologic curiosity. The «lithified potatoes» are orbicular norite which formed at the rim of an intrusion of a gabbroic magma within old sediments approximately 1000 million years ago.

Scientists believe the “potatoes” were formed in convex movements in the magma, possibly due to multiple pulses of magma intruding. New articles will come out on this deposit soon, so stay tuned.

Norway. Stage 5, 13 Aug

Black stone with purple colour. A hammer is in the right corner.

Erythrite after cobalt-sulpharsenides in the Skuterud cobalt mines, Photo: Jan Sverre Sandstad, NGU. 

Do you remember the failed rifting at stage 2 being the base of the current landscape in Bohuslän?

For stage 5, we have moved across the the rift, known as the Oslo Rift. This stage start along the rim of the rift before the cyclists reenter the SW Scandinavian Precambrian basement rocks west of the rift.

The bedrock north of Kongsberg are mainly metamorphosed rocks, and due to the proximity of the volcanic rocks of the Oslo rift, they are very rich in various mineral resources such as cobalt, magnesite and serpentinite.

The cobalt mines of Modum are famous for being the major source of cobalt blue pigment used in Europe during the late 18th and 19th centuries. The largest production came from Skuterud, which is also the type-locality for the cobalt-arsenide skutterudite.

Two cave openings to the cobolt mines. On the top of the mountain there is a wooden fence.

Outside of the cobolt mines in Skuterud. Photo: Jan Sverre Sandstad, NGU. 

Norway. Stage 6, 14 Aug

Maps showing both lineaments and the major roads in the area.

Map showing both lineaments and the major roads in the area.

Have you ever considered how modern infrastructure is affected by geology? Not by superficial processes as land slides or rock falls, or resources needed to maintain the infrastructure, but as deep structures in the bedrock.

The final stage of the Tour of Scandinavia 2022 more or less follow the Ørje Shear Zone/Dalsland Boundary Zone in Sweden until the route turns westward back to Halden. The Ørje Shear Zone was probably formed during the Sveconorwegian Orogeny 1130-900 Ma, yet it is a major feature considering the modern infrastructure and settlement pattern in this part of Norway.

And with this mind-blowing fun fact, this conclude our geological tour. We hope you have enjoyed this geological tour of the basement of SW Scandinavia.