Molasse basin
The weight of the orogenic wedge made the European plate bend downward, forming a deep marine foredeep.
In the Eocene epoch (55 to 34 million years ago) the basin became deeper until north of the developing orogen it formed a small oceanic trench, in which flysch sediments were deposited.
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 evaporites.
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 at its northern rim, slowly rises southwards and can reach more than 1,000 m at its contact with the Alps.
On top of this is the Lower Freshwater Molasse (German: Untere Süsswassermolasse) of Chattian and Aquitanian age (late Oligocene-early Miocene, 28 to 22 million years old).
This second formation therefore consists of fluviatile sands and clays and huge alluvial fan systems (conglomerates and breccias) originating from the Alps to the south.
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.
