Foreland basin

Foreland basins are sedimentary basins, the orogens are upstream. They are tectonically related and occur in the foreland by subsidence of a continental crustal section in front of a ballast advancing orogenic front ceiling.

History

Foreland basin, Eng. foreland basins, are now known for more than 110 years and have also been referred to as such in the classical Geosynklinaltheorie. Kay calls them in his work from 1951 still Exogeosynklinalen.

In the plate tectonics then the term was foreland basin in 1974 by WR Dickinson addressed in the scientific literature, and later executed by C. Beaumont on. It should, however the concept of the foredeep (Franz Eduard Suess, 1909), Eng. foredeep, as it had been used by Miall and Bally 1981, are separated because the foredeep represents only a portion of the foreland basin.

Definition

Foreland basins are tectonic Lithosphäreneintiefungen on or relatively close to the continental margin. You are on continental crust that is subducted in the course of a collision or run over by an oncoming Orogenfront or reversed deferred.

Description

Foreland basin are in the transverse profile of asymmetric nature, its lowest point they have in the immediate vicinity of the deferred fold belt and the thrust front. However, their spatial position is not fixed, but moves with time rapidly towards Konntinentinneres.

Foreland basin caused by a flexure in the continental lithosphere, which is due to the vertical load of the advancing orogen. An immediate consequence of Lithosphärenflexur is the Aufbeulen the continental crust behind her elbow point. The result is a so-called forebulge, which can show up to the surface and then divides the foreland basin. Kratonwärts from the forebulge is the so-called backbulge, a fairly shallow sedimentary basins. Toward Orogen follows the foredeep ( foredeep ) - the deepest part of the foreland basin - and the somewhat shallower wedge -top, which is already located above the Akkretionskeiles.

The temporal evolution of foreland basins is thus directly linked to the advance of the orogenic front of the resulting Mountains. Some pelvis can hereby be severely disrupted in their structure or even completely disappear under tectonic ceilings. Conversely, the sedimentary sequence in the foreland basin valuable clues to the development of the orogen. Thus, for example, from the foreland basin sediments (by fission tracks and closure temperatures of minerals ) time - temperature-pressure paths ( TTP paths ) for the win Orogen.

Sedimentation in foreland basins

The sediment in foreland basins is from two very different Abtragungungsgebieten ( continental shelf sediments on the one hand and orogenic detritus on the other). This has a direct effect on the arrangement of the individual Faziesräume within the basin, which generally align themselves parallel to the longitudinal axis Beck. However, Transverse faults and lineaments in the underlying bedrock can change this somewhat simplistic scheme and dismember the foreland basin into several sub- basins. In some foreland basin, the sediment sideways done (example: Mesopotamia valley - Persian Gulf).

The onset of sedimentation often preceded by a hiatus.

Time can be of the sediment roughly divided into two stages: an initial underfill Beck Stadium (English underfilled basin ) and a final overcrowded Beck Stadium (English overfilled basin ).

During the underfilled stage mostly turbidites, hemipelagic shales and carbonates of the shelf area to the deposit, during the crowded stage clearly outweigh continental Molassesedimente. The foreland basin can ultimately completely silt up and are filled with alluvial fan sediments.

Types of pools

From the genetic point of view, there are two very different types of foreland basins:

• Peripheral foreland basins.
• Foreland basin located behind Intrusivbögen.

Peripheral foreland basins (English peripheral foreland basins ) arise in the course of a continental collision directly on the continental margin, which before Orogenfront plunges directly into an A- subduction zone. When situated behind Intrusivbögen foreland basin (german retro -arc foreland basins ), the thrust front behind a sheet of igneous intrusives, which is much more settled in the continent interior ( Kordillerentypus ). This type is linked to a B- subduction zone, ie in a collision with oceanic crust, resulting in the formation of a magmatic island arc. The already well in Kratoninneren running thrust front is comparable to a backthrust. The retro -arc type can have two very different foreland basin, on the one hand a very flat, thin-skinned basins, on the other hand, a broken pelvis, which is penetrated by towed high basement blocks. The thin-skinned basins are coupled to a steep Subduktionswinkel the broken pelvis at a relatively shallow angle.

Examples

The most impressive example of a peripheral foreland basin is the Indus - Ganges-Brahmaputra lowlands in the south of the Himalayan thrust fault. The Himalayas has several thrust systems ( Main Boundary Thrust, Main Central Thrust, etc.) lifted as a result of the continental collision between the Eurasian plate and the Indian subcontinent since the Middle Miocene around 18 to 20 kilometers, which corresponds to a rate of 70 centimeters per one thousand years. In its southern foreland basin upstream the Siwaliks, which consist of more than 5 km of sediment formed. Characteristic of the Siwaliks is their continued migration to the south with internal thrusts and constant sediment rearrangement.

Other examples of peripheral foreland basins are Mesopotamia and the Persian Gulf ( Zagrosüberschiebung ), the Molasse Basin north of the Alps, the Po -Adriatic basin, the Ostkarpatentrog, the Aquitaine basin and the Ebro basin of the Pyrenees.

Examples of the Kordillerentypus are located on the eastern edge of the Rocky Mountains basin, the Western Interior Seaway which took place later, and the basin on the eastern edge of the Andes ( the Sierras Pampeanas, for example, are a broken pelvis).

In Paleozoic foreland basin of the Lower Old Red Sandstone of south-west Britain, the Silurian - Carboniferous of the central Appalachians, the Upper Carboniferous of the Central European Rhenoherzynikums and possibly the Upper Carboniferous of the Ouachitas came to deposit.