Evolution of the Molasse Basin (Germany, Switzerland)

Abstract

In the Molasse Basin 500–1000 m thick Mesozoic sediments overlie the Variscan basement and locally Permo Carboniferous grabens containing a largely unknown thickness of clastic sediments.The Vindelician basement high extended southwestward from the Bohemian Massif and separated the southern part of the German Basin from the Tethys shelf. Triassic, Early and Middle Jurassic sediments progressively transgressed over this high which became fully inundated during the Late Jurassic. Following a temporary regression, sedimentation resumed in the Early Cretaceous and, after another hiatus, in the Late Aptian to Campanian. During the latest Cretaceous to earliest Tertiary the area of southern Germany became uplifted, resulting in a progressive northwestward truncation of Cretaceous strata and the Late Jurassic carbonates. At the same time the Bohemian Massif became upthrusted along northwest striking wrench faults. Similar faults controlled the upthrusting of the Landshut-Neuoetting High over which some 1,000 m of Mesozoic sediments were eroded. These wrench and thrust tectonics are part of an extensive compressional deformation in Central Europe that is supposed to be caused by the latest Cretaceous-earliest Tertiary collision of the Adriatic-African and European plates during the Alpine orogeny.The area subsided again during the Late Eocene and developed into the Molasse Basin proper in which Oligocene to Miocene elastics reach a thickness of some 5.000 m near the Alpine thrust front.Subduction and flexuring of the foreland caused numerous essentially basin-parallel synthetic and antithetic normal faults; the latter form the primary traps for oil and gas accumulations in the Molasse Basin.