Central Alps – Flysch and Molasse

Flysch and Molasse are terms that describe different sets of sedimentary facies associated with orogenic belts. Molasse is defined as terrestrial and shallow marine deposits formed nearest the rising mountain front. It consists of various interbedded rock types including conglomerates, sandstones, and shales. The molasse on the other hand is made up of deep marine sediments deposited in the distal part of the orogenic sedimentary wedge.
In the Alps (where these terms were originally defined), the flysch and molasse was deposited north of the Alps throughout the development of the Alps from the Cretaceous to the present. Prior to this time, the Alpine area was covered with what is known as the Tethys Ocean. The Tethys Ocean extended from Spain all the way to Australia and Indonesia. As rifting in the Tethys Ocean stopped and southward subduction began, sediment began accumulating in front of the growing mountain front. As the Apulian plate continued to override the European plate the weight of the Apulian plate and the sediment accumulating on the European plate began to flex the subducting plate adding to the accumulation space of the basin. The interplay of accretionary loading and sedimentation continues as the fold and thrust belt of the advancing orogeny. Eventually the fold and thrust belt overthrusts the oldest part of the flysch and molasse basin.
The Helvetic nappes discussed in the last post overthrust this basin over 10 kilometers. This overthrusting of the Helvetic nappes raised the orogenic wedge to a critical taper. This means the strength of the rocks do not allow for the angle of the orogenic wedge to exceed this critical taper forcing the convergence to be accommodated further into the foreland. As thrust faults cut through the more distal portions of the foreland basin, a large part of the basin is caught up in the fold and thrust belt (the Jura Mountains) and forms a piggy-back basin (the Geneva basin) and extends the active portion of the flysch and molasse basin north of the Jura Mountains.
Sub-Helvetic Molasse
Flute and Cast structures
Zoophycos trace fossil
More flutes
Ooids in the foreland basin sediments
The piggy back basin with Zurich  in the middle and the high peaks of the Alps above the clouds.
Sauropod tracks in the molasse
Marbach, Switzerland

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