Molasse basin
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The Molasse basin (or North Alpine foreland basin) is a
In
Geographic location
The Molasse basin stretches over 1000 kilometers along the long axis of the Alps, in
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 over each other.
Tectonic history
Before the development of the Molasse basin, in the
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
Stratigraphy
The molasse deposits in the basin can be up to 6 kilometers thick.
The lowermost formation is the (early Oligocene, 34 to 28 million years old) and it consists of shallow marine sand, clay and marl.
On top of this is the
By 22 million years ago, the Alpine foreland was flooded again due to tectonic subsidence. A shallow (intertidal) marine environment formed from Lyon to Vienna. 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 to Langhian age (early Miocene, 22 to 16 million years old).
More tectonic uplift caused the sea to retreat one final time and during the Serravallian, Tortonian and Messinian/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.[2]
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
- Labhart, T.; 2005: Geologie der Schweiz, Ott Verlag, ISBN 3-7225-0007-9.