Tectonic Salt Structure

Tectonic Salt Structure

 

a type of folded deformation of the sedimentary layer of the earth’s crust. It is associated with the presence of fairly thick (hundreds of meters or more) salt-bearing deposits (rock salt or potassium salts) in the basement or middle part of the section of the layer.

Tectonic salt structures may occur where a sediment has a higher plasticity and lower density than that of the other consolidated sedimentary rocks. The inversion of densities—relatively light salts below and denser rocks above—leads to a gravitational upsurge of the salts, which has been confirmed experimentally, and to the formation of salt pillows followed by the formation of salt domes. Such a dome has a salt core, or plug, that rises and pierces the younger rocks of the enclosing sediments. Below the surface, the domes sometimes merge into walls. The core of a dome may crop out at the surface or remain concealed beneath a cover of overlying rocks, in which a network of fractures forms. These fractures are tension faults, along which a graben-like subsidence of the flanks of the fold often occurs. In foredeeps and intermontane troughs of folded regions, where tectonic salt structures develop under conditions of lateral pressure from adjacent folded structures, salt-bearing formations appear in the cores of linear folds, often along the lines of tectonic faults. The shapes of some salt structures are shown in Figure 1.

Figure 1. Shapes of salt structures (according to F. Trushelm): (1) underlying rock, (2) salt, (3) surrounding strata

Deposits of petroleum and gas are often found in the arches and limbs of salt domes and anticlines. Salt cores are worked for rock and potassium salts.

Classic regions of tectonic salt structures include the Caspian Basin, the basin of the Gulf of Mexico, and the coast of the Gulf of Mexico.

Tectonic salt structures show up in deposits of different ages from the late Precambrian (South Australia) to the Neogene (the Tadzhik Depression). They are associated primarily with salt-bearing strata of the following ages: Wendian-Lower Cambrian (the Persian Gulf region and the Irkutsk Amphitheater), Devonian (the Pripiat’, Dnieper-Donets, Khatanga, and Viliui basins), Permian (the Central European [Strasfurt] and Caspian basins, the Cisural Trough [Solikamsk], and the Sverdrup Basin in the Canadian Arctic Archipelago), Middle and Upper Triassic (northwest Africa and the Aquitaine Basin in France), Upper Jurassic-Lower Cretaceous (the basin of the Gulf of Mexico and the Gabon and Angola basins), and Oligocene-Miocene (the Cis-carpathian [Kalush, Wieliczka] and Transcarpathian troughs [Solotvina] and the Transylvanian Basin).

V. E. KHAIN

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