The Molasse basin (or North Alpine foreland basin) is a

foreland basin A foreland basin is a structural basin that develops adjacent and parallel to a mountain belt. Foreland basins form because the immense mass created by crustal thickening associated with the evolution of a mountain belt causes the lithospher ...

north of the

Alps The Alps () are some of the highest and most extensive mountain ranges in Europe, stretching approximately across eight Alpine countries (from west to east): Monaco, France, Switzerland, Italy, Liechtenstein, Germany, Austria and Slovenia. ...

which formed during the

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

and

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

epochs In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided by ...

. The basin formed as a result of the

flexure A flexure is a flexible element (or combination of elements) engineered to be compliant in specific degrees of freedom (mechanics), degrees of freedom. Flexures are a design feature used by design engineers (usually mechanical engineers) for prov ...

of the European plate under the weight of the

orogen An orogenic belt, orogen, or mobile belt, is a zone of Earth's crust affected by orogeny. An orogenic belt develops when a continental plate crumples and is uplifted to form one or more mountain ranges; this involves a series of geological proc ...

wedge A wedge is a triangle, triangular shaped tool, a portable inclined plane, and one of the six simple machines. It can be used to separate two objects or portions of an object, lift up an object, or hold an object in place. It functions by conver ...

of the Alps that was forming to the south. In

geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...

, the name "molasse basin" is sometimes also used in a general sense for a synorogenic (formed contemporaneously with the

) foreland basin of the type north of the Alps. The basin is the type locality of

molasse __NOTOC__ In geology, "molasse" () are sandstones, shales and conglomerates that form as terrestrial or shallow marine deposits in front of rising mountain chains. The molasse deposits accumulate in a foreland basin, especially on top of flys ...

, a

sedimentary Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedime ...

sequence of conglomerates and

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

s, material that was removed from the developing mountain chain by

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

and

denudation Denudation is the geological process in which moving water, ice, wind, and waves erode the Earth's surface, leading to a reduction in elevation and in relief of landforms and landscapes. Although the terms erosion and denudation are used interchang ...

, that is typical for foreland basins.

Geographic location

The Molasse basin stretches over 1000 kilometers along the long axis of the Alps, in

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

Switzerland Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...

Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

and

Austria Austria, formally the Republic of Austria, is a landlocked country in Central Europe, lying in the Eastern Alps. It is a federation of nine Federal states of Austria, states, of which the capital Vienna is the List of largest cities in Aust ...

. The west end is at

Lake Geneva Lake Geneva is a deep lake on the north side of the Alps, shared between Switzerland and France. It is one of the List of largest lakes of Europe, largest lakes in Western Europe and the largest on the course of the Rhône. Sixty percent () ...

, where the basin's

outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth and other terrestrial planets. Features Outcrops do not cover the majority of the Earth's land surface because in most p ...

is just 20 km wide. Further to the northeast the basin becomes wider. It forms the subsurface of the Swiss Mittelland and reaches its widest (circa 130 km) in the

Bavaria Bavaria, officially the Free State of Bavaria, is a States of Germany, state in the southeast of Germany. With an area of , it is the list of German states by area, largest German state by land area, comprising approximately 1/5 of the total l ...

n foreland of the Alps. From Amstetten to

Sankt Pölten Sankt Pölten (; Central Bavarian: ''St. Pödn''), mostly abbreviated to the official name St. Pölten, is the capital and largest city of the States of Austria, State of Lower Austria in northeast Austria, with 55,538 inhabitants as of 1 Januar ...

the basin forms a narrow band, just 10 km wide. After that it widens again to the east. North of the

Danube River The Danube ( ; see also other names) is the second-longest river in Europe, after the Volga in Russia. It flows through Central and Southeastern Europe, from the Black Forest south into the Black Sea. A large and historically important riv ...

it connects with the

Vienna basin The Vienna Basin (, , , Hungarian: ''Bécsi-medence'') is a geologically young tectonic burial basin and sedimentary basin in the seam area between the Alps, the Carpathians and the Pannonian Plain. Although it topographically separates the Al ...

, and is thus connected with the

Pannonian Basin The Pannonian Basin, with the term Carpathian Basin being sometimes preferred in Hungarian literature, is a large sedimentary basin situated in southeastern Central Europe. After the Treaty of Trianon following World War I, the geomorpholog ...

further east. The region where the molasse crops out is divided into two: the ''Subalpine Molasse zone'' along the Alps and the ''Foreland Molasse zone'' further into the foreland. In the Foreland Molasse zone the molasse sediments are relatively undisturbed; in the Subalpine Molasse zone the beds are often tilted, folded and

thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that ...

over each other.

Tectonic history

Before the development of the Molasse basin, in the

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

era An era is a span of time. Era or ERA may also refer to: * Era (geology), a subdivision of geologic time * Calendar era Education * Academy of European Law (German: '), an international law school * ERA School, in Melbourne, Australia * E ...

, the region was covered by a shallow sea that was the northern margin of the Alpine part of the

Tethys Ocean The Tethys Ocean ( ; ), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean during much of the Mesozoic Era and early-mid Cenozoic Era. It was the predecessor to the modern Indian Ocean, the Mediterranean Sea, and the Eurasia ...

(

Valais Ocean The Valais Ocean is a subducted oceanic basin which was situated between the continent Europe and the microcontinent Iberia or so called Briançonnais microcontinent. Remnants of the Valais ocean are found in the western Alps and in tectonic win ...

in the west, Tethys Ocean proper in the east). The Molasse basin was formed when the orogenic wedge of the forming Alps was pushed north over the European

continental margin A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental marg ...

, due to the convergent movement of the

European European, or Europeans, may refer to: In general * ''European'', an adjective referring to something of, from, or related to Europe ** Ethnic groups in Europe ** Demographics of Europe ** European cuisine, the cuisines of Europe and other West ...

and

Apulian plate The Adriatic or Apulian plate is a small list of tectonic plates, tectonic plate carrying primarily continental crust that broke away from the African plate along a large transform fault in the Cretaceous period. The name Adriatic plate is usu ...

s during the

Paleogene The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...

period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

. The weight of the orogenic wedge made the European plate bend downward, forming a deep marine foredeep. In the

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

epoch (55 to 34 million years ago) the basin became deeper until north of the developing orogen it formed a small

oceanic trench Oceanic trenches are prominent, long, narrow topography, topographic depression (geology), depressions of the seabed, ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers ...

, in which

flysch Flysch () is a sequence of sedimentary rock layers that progress from deep-water and turbidity flow deposits to shallow-water shales and sandstones. It is deposited when a deep basin forms rapidly on the continental side of a mountain building ep ...

sediments were deposited. The huge amounts of sediments eroded from the forming mountain chain filled the basin and made it shallower. During the Oligocene and Miocene epochs (more exactly, between 10 and 30 million years ago), shallow marine to continental molasse was deposited in the basin. Around 10 to 5 million years ago, tectonic uplift had raised the basin so high that net sedimentation stopped. From the south, the molasse deposits were overthrust about 10 kilometers by the

Helvetic nappes The Helvetic nappes ({{langx, de, Helvetische Decken) are a series of nappes in the Northern part of the Alps and part of the Helvetic zone. They consist of Mesozoic limestones, shales and marls that were originally deposited on the southern cont ...

, which caused the deformation in the Subalpine Molasse zone. The

Jura mountains The Jura Mountains ( ) are a sub-alpine mountain range a short distance north of the Western Alps and mainly demarcate a long part of the French–Swiss border. While the Jura range proper (" folded Jura", ) is located in France and Switzerla ...

, a

fold and thrust belt A fold and thrust belt is a series of mountainous foothills adjacent to an orogenic belt, which forms due to contractional tectonics. Fold and thrust belts commonly form in the forelands adjacent to major orogens as deformation propagates outwards ...

along the present Swiss-French border, also originated from this tectonic phase. In some places in the Jura mountains, molasse deposits were folded together with older Mesozoic

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

s. In present-day central Switzerland, however, the molasse formed a thick competent mass that was thrust northward in one piece over a decollement horizon at the base of the Mesozoic, in

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

evaporite An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as oce ...

s. Deformation instead localized further north, thus forming the relatively flat Swiss Mittelland between the Alps and the Jura Mountains. The Swiss part of the Molasse basin is now between the Alps and the Jura mountains, as a large

piggyback basin A piggyback basin (also piggy-back, thrust-sheet-top, detached, or satellite basin) is a minor sedimentary basin developed on top of a moving thrust sheet as part of a foreland basin system. Piggyback basins form in the wedge-top depositional zone ...

. In the

Eastern Alps The Eastern Alps are usually defined as the area east of a line from Lake Constance and the Alpine Rhine valley, up to the Splügen Pass at the Main chain of the Alps, Alpine divide, and down the Liro (Como), Liro River to Lake Como in the south. ...

an external mountain range such as the Jura Mountains never developed. Due to the last phase of tectonic uplift around 5 million years ago, the molasse in the Swiss Plateau, the South Bavarian plain and Eastern Austria is now 350 to 400 meters above

sea level Mean sea level (MSL, often shortened to sea level) is an mean, average surface level of one or more among Earth's coastal Body of water, bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical ...

at its northern rim, slowly rises southwards and can reach more than 1,000 m at its contact with the Alps.

Stratigraphy

The molasse deposits in the basin can be up to 6 kilometers thick. Lithostratigraphically, this molasse is treated as a

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...

divided into four formations. This division is made on whether the

sedimentary facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with distinctive characteristics. The characteristics can be any observable attribute of rocks (such as their overall appearance, composition, or con ...

is continental or marine. The lowermost formation is the '' Lower Marine Molasse'' (in

German German(s) may refer to: * Germany, the country of the Germans and German things **Germania (Roman era) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizenship in Germany, see also Ge ...

: ''Untere Meeresmolasse''). Its age is

Rupelian The Rupelian is, in the geologic timescale, the older of two age (geology), ages or the lower of two stage (stratigraphy), stages of the Oligocene epoch (geology), Epoch/series (stratigraphy), Series. It spans the time between . It is preceded b ...

(early Oligocene, 34 to 28 million years old) and it consists of shallow marine sand, clay and marl. On top of this is the '' Lower Freshwater Molasse'' (German: ''Untere Süsswassermolasse'') of

Chattian The Chattian is, in the geologic timescale, the younger of two ages or upper of two stages of the Oligocene Epoch/Series. It spans the time between . The Chattian is preceded by the Rupelian and is followed by the Aquitanian (the lowest stage ...

and

Aquitanian Aquitanian may refer to: *Aquitanian (stage), a geological age, the first stage of the Miocene Epoch *Aquitanian language, an ancient language spoken in the region later known as Gascony *Aquitani (or Aquitanians), were a people living in what is n ...

age (late Oligocene-early Miocene, 28 to 22 million years old). Due to a

eustatic Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised ...

drop of the sea level combined by tectonic uplift, the basin was now above sea level. This second formation therefore consists of fluviatile sands and clays and huge

alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to Semi-arid climate, semiar ...

systems (conglomerates and breccias) originating from the Alps to the south. By 22 million years ago, the Alpine foreland was flooded again due to tectonic subsidence. A shallow (

intertidal The intertidal zone or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various sp ...

) marine environment formed from

Lyon Lyon (Franco-Provençal: ''Liyon'') is a city in France. It is located at the confluence of the rivers Rhône and Saône, to the northwest of the French Alps, southeast of Paris, north of Marseille, southwest of Geneva, Switzerland, north ...

Vienna Vienna ( ; ; ) is the capital city, capital, List of largest cities in Austria, most populous city, and one of Federal states of Austria, nine federal states of Austria. It is Austria's primate city, with just over two million inhabitants. ...

. In this environment the third formation, the '' Upper Marine Molasse'' (German: ''Obere Meeresmolasse''), was formed. It consists of marine sands, clays and marls and new fan conglomerates and is of

Burdigalian The Burdigalian is, in the geologic timescale, an age (geology), age or stage (stratigraphy), stage in the early Miocene. It spans the time between 20.43 ± 0.05 annum, Ma and 15.97 ± 0.05 Ma (million years ago). Preceded by the Aquitanian (sta ...

Langhian The Langhian is, in the ICS geologic timescale, an age or stage in the middle Miocene Epoch/Series. It spans the time between 15.97 ± 0.05 Ma and 13.65 ± 0.05 Ma (million years ago) during the Middle Miocene.GeoWhen (2007) The Langhian was ...

age (early Miocene, 22 to 16 million years old). More tectonic uplift caused the sea to retreat one final time and during the

Serravallian The Serravallian is, in the geologic timescale, an List of time periods, age or a stage (stratigraphy), stage in the middle Miocene epoch (geology), Epoch/series (stratigraphy), Series, which spans the time between 13.82 annum, Ma and 11.63 Ma (m ...

Tortonian The Tortonian is in the geologic time scale an age or stage of the late Miocene that spans the time between 11.608 ± 0.005 Ma and 7.246 ± 0.005 Ma (million years ago). It follows the Serravallian and is followed by the Messinian. The Tort ...

and

Messinian The Messinian is in the geologic timescale the last age or uppermost stage of the Miocene. It spans the time between 7.246 ± 0.005 Ma and 5.333 ± 0.005 Ma (million years ago). It follows the Tortonian and is followed by the Zanclean, the fir ...

/ Pontian ages (late Miocene, 16 to 5 million years ago), the basin was in a continental facies again. The fluviatile sands and clays and fan conglomerates of this time form the '' Upper Freshwater Molasse'' (German: ''Obere Süsswassermolasse''), the topmost molasse formation.Labhart (2005), pp. 20-24 Around 5 million years ago a phase of uplift occurred in the Alps. During this phase the Molasse basin ceased to be an area of net sedimentation.

References

Literature

* ; 2005: ''Geologie der Schweiz'', Ott Verlag, . {{coord, 47, 46, 08, N, 10, 08, 25, E, region:DE-BY_type:landmark_source:kolossus-dewiki, display=title Structural geology Sedimentology Geology of the Alps Geology of Switzerland Geology of Austria Geology of Germany