Molasse basin

As Molasse Basin, also foothills trough in the regional geology of the Alpine countries of the area occupied by Molassesedimenten area is referred to on the northern edge of the Alps. The term Molasse Basin is also commonly referred to in a sedimentary basin that receives the weathering debris of a rising mountain range (see molasses ).

The treated here North Alpine Molasse Basin is divided into a larger northern area, the Vorlandmolasse with rocks in predominantly undisturbed storage, and a narrower southern region immediately on the northern edge of the Alps, the Subalpine Molasse ( Molasse, Faltenmolasse ) with verschuppten and steeply set Molassegesteinen.

Occurrence

The Molasse Basin is located in front of the entire northern Alpine front. It extends with a length of about 1,000 km over parts of France, Switzerland, Germany and Austria. At its western end by Lake Geneva, it is about 20 km wide, engages in an easterly direction far to the north and reached the Bavarian Alpine foothills its greatest width of nearly 130 km. Further east, the width in the amount of Amstetten down to about 10 km; from there it runs as a narrow strip to about St. Pölten, widens then - in a northeasterly direction pivoting - up to about 40 km wide, and is north of the Danube into the Carpathian foredeep. Geologically it is here on the Vienna Basin with the Pannonian Plain in conjunction.

Formation

The Molasse Basin formed in a foreland or peripheral sink that had emerged in the final stages of development prior to the alpine Alps, when the European continental plate herabbog under the weight of the overlying rock mass. This foreland sink was at the beginning a relatively narrow inlet ( Molasse ), which rapidly filled with sediments and silted. Then the earth's crust sank again from so far that the Molasse Basin was with the surrounding maritime areas in conjunction. This is supported by, among others, the Haifaunen, which can be found at various locations, such as in the Erminger Turritellenplatte at Ulm. The Molasse palaeogeographic is attributed to the so-called Paratethys, which emerged from the Mesozoic Tethys Ocean.

In the course of the Tertiary rivers verfrachteten large amounts of eroded material from the Alps to be collected in the foreland basin. With the discharge of the rivers from the Alps in the flat regions, the flow rate generally fell sharply. Near the edge of the Alps, therefore, the biggest rocks were deposited, because they could no longer be carried as Alluvialgeschiebe due to their weight from the transporting medium, the water. Thus arose conglomerates and coarse sandstones, in particular characterize the Freshwater Molasse. Based on the grain size bed several compartments former Alpine rivers can be distinguished. The most prominent example of such a bed compartments is the Napfbergland on the Swiss Plateau. Smaller particle sizes could, however, be also carried as suspended matter far into the basin and formed clayey or marly sediments that are especially typical of the Marine Molasse. Times of low erosion activity are reflected in layers with a total of smaller grain sizes resist. So, in the Alps near the foothills a powerful depending on the region to over 4000 m Molasse sequence, which is divided into a number of subunits. Often the Molassesedimente remains of plants and other organic remains contained. Therefore, it came to a certain extent, to the formation of oil and coal. The Graupensande in the northwest of the basin also contain Bohnerz.

Surface forms

The Molasse Basin stands out in the Vorlandmolasse over long distances by rolling hills and broad valleys of depression. In Switzerland, the Mittelland has significantly greater height differences as the Bavarian and Austrian Alpine foothills. In the Subalpine Molasse pull parallel to the Alps long ridges with inclined ribs conglomerate; their ridges are rounded and do not predominantly steep rock walls.

The south of the Molasse Basin was about Shapes by the glaciers of the Ice Ages, which created a variety of glacial landforms ( glacial deposits ) with trough-shaped valleys and elongated ridges.

The river network is directed away from the Alps, only at the northern edge of the Vorlandmolasse the Danube carries the majority of the rivers eastward to the Black Sea from. West of the Danube source drain the Rhine and its tributaries the Vorlandmolasse in the North Sea. The extreme western end is drained by the Rhône and some of its tributaries to the west and the Mediterranean.

Layer sequence

The rocks of the Molasse Basin were deposited in the Upper Eocene to the Upper Miocene. They are due to the prevailing conditions of deposition - divided into four main groups - marine or terrestrial.

• Lower Marine Molasse, Rupelium, million years ago, about 34-28
• Lower Freshwater Molasse, Chattian and Aquitanian, in about 28 to 22 million years
• Upper Marine Molasse, Burdigalium and Langhium, million before about 22 to 16 years
• Upper Freshwater, Serravallium, Tortonian and Pontium, above about 16 and 5 million years

In the eastern Molasse Basin, the Lower Freshwater Molasse goes in marine strata. It is designated as a younger part of the Lower Marine Molasse, which represented the West Lower Freshwater Molasse missing.

Swell

Literature and maps

• Geological Map of Switzerland 1:500 000 Swiss Geological Commission, 1980.
• Hans Heierli: Geological hiking Switzerland. Part 1: The geological foundations. 2nd edition. Ott, Thun 1983, ISBN 3-7225-6282-1.
• Geological Map of Bavaria 1:500 000 with explanatory notes. 4th edition. Bavarian Geological State Office, Munich 1996.
• Geological map of the Republic of Austria with tectonic structure 1:1,000,000. Revised reprint. Geological Survey of Austria Vienna, Publishing Freytag & Berndt, Vienna 1986.