Did you know that parts of Switzerland were once covered by an ancient sea?
Learn more about the evolutionary history and geology of Switzerland in this article. If you would like to know what the ground beneath our feet looks like, we recommend a visit to the Grimsel Test Site or Mont Terri Rock Laboratory. In the latter, Nagra is working with other organisations to investigate a rock that plays a crucial role in the disposal of radioactive waste: the Opalinus Clay.
Stop by our meeting point in Stadel or visit us in one of the research laboratories. We would be pleased to show you what we are currently working on.
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Overview of Switzerland’s geological evolution
Marine sediments, the folding of the Alps and the Jura Mountains, the erosion of mountains as well as glaciation all shape the way Switzerland looks today. The above map shows the geological features and the distribution of the various rock types found at the surface.
In simplified terms, Switzerland can be divided into four distinct units:
- Folded and Tabular Jura in the north and north-west consisting of limestones, marls (composite rock consisting of limestone and clay), clays and anhydrite/gypsum
- Swiss Plateau and the Molasse Basin, filled with mountain deposits consisting of sandstones, nagelfluh, silt and marls
- Northern Alps, including the Helvetic Zone, consisting primarily of marl-rich sediments that were deposited during the Mesozoic Period
- Central and Southern Alps with the Crystalline Zone, consisting primarily of granites and gneisses that crystallised through the solidification of magma in the earth’s interior
Cross-section through Switzerland
Troughs form in the crystalline basement
Crystalline plutonic, metamorphic and dyke rocks were formed in the earth’s crust and make up the crystalline basement (number 1 in the map “Cross-section of Switzerland” above). This was formed over hundreds of millions of years by orogenic processes.
During the Permian and Carboniferous Periods over 250 million years ago, troughs (number 2) sank into the crystalline basement. These were subsequently filled with eroded material from the surrounding mountains. The remains of one such Permo-Carboniferous Trough are located in Northern Switzerland between Frick and Konstanz.
Jurassic Sea covers Switzerland
During most of the Jurassic Period, Switzerland was covered by a sea. Sedimentary rocks (3) that now cover the older bedrock were once deposited on the ocean floor where they gradually solidified.
The Alps were formed by the collision of the Adriatic and the Eurasian tectonic plates during the Late Cretaceous and Tertiary Periods. During a comparatively late phase in the formation of the Alps, the rocks of the Helvetic sedimentary zone were broken down into rock stacks, folded and transported northwards (4). Situated between these stacks is eroded material, so-called Flysch (5) that had previously been deposited in the sea during the formation of the Alps. Further eroded material generated by the uplifting Alps, known as molasse, accumulated in the Molasse Basin (7) located on the northern flank of the Alps.
The formation of the Alps led to the folding of the Jura Mountains
The pressure from the emerging Alps extended into Northern Switzerland: sedimentary rocks were detached from the crystalline bedrock, thus creating the Folded Jura (6).
Geological history
(in millions of years)
Carboniferous: -358.9 to -298.9
Permian: -298.9 to -252.2
Triassic: -252.2 bis -201.3
Jurassic -201.3 to -145
Cretaceous: -145 to -66
Tertiary (Paleogene & Neogene): -66 to -2.588
Quaternary: -2.588 to 0
Folded Jura and Tabular Jura
Both the Folded and the Tabular Jura mainly consist of limestone, marl and clay rocks as well as anhydrite and gypsum. The Tabular Jura, which extends from north-western Switzerland to the Schaffhausen region, forms a cuesta landscape due to the varying erodibility of these rock types. Erodibility describes the susceptibility or resistance of a rock to erosion.
In north-western Switzerland in particular, fault zones extending from north to south further divide these cuestas into blocks. This typical surface structure of the Tabular Jura with higher areas and valleys is also known as fault-block mountains. These mountains were formed, along with the Rhine Graben, around 40 million years ago during the Cenozoic Period. Fault zones are fractures in the rock formations with displacement of the individual rock areas relative to one another ranging from several centimetres up to several kilometres.
The Folded Jura describes an arc extending from the Geneva region and neighbouring France in the west to the Swiss town of Baden in the east. In the Folded Jura, the sedimentary rocks were compressed and folded as a result of the Alpine orogeny. A classic example is provided by the massive limestone deposits at the Creux du Van (in Canton Neuchâtel). The Folded Jura is only occasionally breached by narrow transverse valleys, or gorges. Roads often follow these gorges. Where they cannot, they have to go through a tunnel or over a mountain pass.
Swiss Plateau with the Molasse Basin
The Swiss Plateau lies between the Jura Mountains in the north and the Alps in the south and extends from Lake Constance to Lake Geneva. It is characterised by distinctive river courses and lakes.
The crystalline basement is located deep below the Swiss Plateau. It is covered by sedimentary sequences from the Mesozoic Period, particularly marine sediments such as limestones and clays. Above this lies the so-called Molasse, which consists of eroded material (rock fragments, sand, silt and clays) from the developing Alps. In the final phase of the Alpine orogeny, the earth’s crust sank under the weight of the mountains and a depression was formed in the Alpine foreland. For about 30 million years, this depression was continuously filled with eroded material that rivers transported northwards from the Alps – eventually forming the Molasse Basin.
Diverse fossils
Eroded material from the Alps was deposited in lakes and river valleys; as a result, there are two types of Molasse: Marine and Freshwater. The sediments were deposited according to grain size: finer particles such as clay platelets were transported far into the sea, as far as the edge of today’s Jura Mountains. Coarser particles could not remain suspended in the rivers for as long and settled in the rivers closer to the Alps, for example as gravel beds. Marine Molasse is fine-grained and consists primarily of marl, sandstone, silt and clay. Freshwater Molasse has coarser-grained components such as nagelfluh and sandstone.
Various layers are rich in fossils: Freshwater Molasse contains leaves, freshwater snails and mussels. Marine Molasse contains sea snails and mussels as well as shark teeth.
History of the Marine and Freshwater Molasses
Seawater entered the depression that was formed in the Swiss Plateau during the final phase of the Alpine orogeny. Sediments such as marl and sandstones that were deposited there around 35 to 30 million years ago belong to the Lower Marine Molasse.
Due to the increased rate of uplift of the Alps around 30 million years ago, larger amounts of eroded material were carried to the Molasse Basin. As a result, the sea soon became land again. The sediments that were deposited primarily in riverbeds 30 to 20 million years ago belong to the Lower Freshwater Molasse. Coarser-grained components were deposited as nagelfluh. In a later phase of the Alpine orogeny, the molasse rocks located close to the Alps were compressed, moved and uplifted from the Molasse Basin (forming, for example, the Rigi Mountain).
When the sea level rose about 20 million years ago, the Swiss Plateau was again flooded by the sea. In this narrow, shallow sea, sediments from the Upper Marine Molasse such as sandstone and marl were deposited between around 20 and 18 million years ago. At the same time, deltas and alluvial fans were formed.
The sea retreated again between 18 and 14 million years ago, forming many lakes and rivers in the Swiss Plateau as well as large alluvial fans at the Hörnli and Napf mountains with a lot of gravel, and extensive floodplains with sand, silt and mud. These sediments of the Upper Freshwater Molasse were compressed into conglomerates such as nagelfluh, sandstones and marls.
Ice ages shaped the Swiss Plateau
Unconsolidated rocks (gravel, scree, sand, silt, clay, etc.) from the ice ages of the last two million years were transported by rivers and glaciers and overlie the Molasse today.
Glaciers and meltwater possess great erosive force and have significantly shaped the present-day topography of the Swiss Plateau. This is apparent in the many elongated lakes running from south-south-east to north-north-west along the Alpine fringe, whose bedrock frequently lies beneath thick layers of unconsolidated rocks. These glacial unconsolidated rocks do not provide solid ground and make construction difficult, but they do provide resources in the form of gravel and drinking water. Occasionally, mammoth teeth are found in these glacial unconsolidated rocks.
Northern Alps with the Helvetic Zone
The Swiss Alps can be divided into the Northern, Central and Southern Alps. The entire Alpine range, however, can also be categorised in other ways.
The so-called Helvetic Zone forms the northern margin of the Alps from Lake Thun to the Rhine valley. It consists of limestone- and marl-rich sediments that were deposited in a shallow sea (Tethys Ocean) in the period from 250 to 65 million years ago.
Whole mountains shifted to the north
The pressure created by the Alpine orogeny deformed the rocks in the region of the Alpine belt. Many of the sediments from the Tethys Ocean are no longer located where they were initially deposited. This can be observed in the Helvetic Zone: during a late phase of the Alpine orogeny, Helvetic sediments were detached from the crystalline basement, folded and transported up to 50 kilometres to the north-west due to pressure from the African continental plate advancing from the south. Today, they are visible in the form of thick stacks of nappes.
The soft layers of marl and slate contained in blocks of rock served as a lubricant. The Säntis, Titlis and Churfirsten mountains are examples of Helvetic nappes.
Central and Southern Alps with the Crystalline Zone
The Swiss Alps form the central part of the entire Alpine range that extends from Mediterranean Nice all the way to Vienna. Aside from sedimentary rocks, the high peaks and glaciers typical of the Central Alps also contain crystalline and metamorphic rocks.
Many peaks are still pointed and sharp-edged because they were spared during the Ice Ages, when ice neither covered nor eroded them.
Africa and Europe collide
From a geological point of view, the Alps are where Africa meets Europe. The African plate has been moving northwards over the last 130 million years and is pushing against the Eurasian continent. The formation of the Alps began at the end of the Cretaceous Period around 80 million years ago as a result of the collision of the African and European plates. This process reached its apex about 30 million years ago.
Due to the thrust from the south and the compression of the rock masses, these rocks shifted not only upwards but also downwards. The thickness of the continental crust increased to well over 50 kilometres.
The Alps are like a floating iceberg
The Alps primarily consist of continental crust, which has a lower density than the underlying mantle. Due to the thickening that occurred during the Alpine orogeny, the continental crust in the Alpine region is thicker than in the foreland. The situation can be compared to an iceberg floating on water. Ice has a lower density than water. When the tip of an iceberg melts, it rises from the water until equilibrium has been restored.
The Alps are also losing mass due to weathering and erosion. The Alps were only just forming when material was already being eroded by processes involving gravity, flowing water or wind. This material was deposited in the Swiss Plateau as molasse. This redistribution of sediments was intensified during glaciations that took place in more recent times.
Earthquakes caused by uplift of the Alps
The area around Brig and Chur is uplifting by up to 1.5 millimetres per year. Earthquakes occur more frequently in this area. The continuous uplift and deformation, as well as the associated erosion, are important factors that rule out the Alpine region as a suitable location for a high-level waste repository.
Central massifs with crystalline basement
The crystalline basement in the Central Alps is visible at the surface. Central massifs, such as the Aar, Gotthard or Mont Blanc Massifs in the south-west of Switzerland, consist mainly of granitic rocks and gneisses. The pressure created by the Alpine orogeny strongly deformed the rocks along the Alpine belt. Both the Aar and the Gotthard Massifs were compressed, but they were not moved away from their original location. These massifs are surrounded by sediments that were overprinted metamorphically.
At the Grimsel Test Site, Nagra is researching the disposal of radioactive waste together with partner organisations. The research laboratory is built into the granitic rocks of the Aar Massif.
Marked fault zone through Ticino
Penninic crystalline nappes lie further to the south in Ticino, and beyond them lies the “Insubric Line”, a prominent fault zone traversing the Alps from east to west where the Adriatic and European plates meet. The Southern Alps lie to the south of this line, and they consist of crystalline rocks and also, in the area south of Lugano, of sediments. The Central Alps, including the Penninic nappes, as well as a large part of the Southern Alps, therefore consist of crystalline.