Salt dome

A salt dome, Salzdiapir or salt dome is a great accumulation of solid, but fluent in geological time rock salt deep underground, which usually has a mushroom-like or vice versa, drop-like shape. Especially elongated, tall and narrow salt domes hot salt walls, rather flat and wide -trained salt accumulations are called salt pillows. A salt dome in the true sense can be several thousand feet high and go up to the surface.

Structure and Formation

1877 formulated Carl Ochsenius the barrier theory or emerging theory about the origin of salt deposits. The formation of a salt dome on the example of the Zechstein Sea in Central Europe can be described as follows:

• Before about 260 million years ago ( in the upper Permian in Central Europe also called Zechstein ) existed in many parts of the world a very dry and hot ( arid ) climate, as well as in Central Europe. In parts of what is now northern central Europe and the North Sea today's space, the Earth's crust dropped off and formed a basin structure. The basin floor dropped relatively quickly below the level of the former sea levels. A grave breach between Norway today and today's Greenland, which at that time was still connected directly to Europe, formed a connection with the ocean in the north, so that the basin was filled with sea water. This is according to the shallow sea deposits, which it left, called the Zechstein Sea, the basin in which it spread, as Zechsteinbecken (the " Zechstein " is also named after these deposits ).
• An occurring every now and then interrupting the water exchange with the ocean and the dry hot climate led to multiple, more or less complete evaporation of the water. Characterized the induced increase in the concentration of dissolved salts in seawater resulted in the precipitation and deposition of carbonates ( limestone ), especially sulphates (mainly gypsum) and chlorides (mainly rock salt ).
• After less than 10 million years, this interplay was terminated from evaporation of sea water and replenishment of the basin and by further lowering ( subsidence ) of the Earth's crust now 500 to 1000 meters in thickness having salt layers were deposits of the geological age of the Triassic, Jurassic and Cretaceous superimposed. The salt layers were sunk by the increasingly powerful overburden layer and continued subsidence of the ground to a depth of about 3000 meters. Since the salt plastic reacts under pressure - similar to ice and glacier movements - also owns and less dense than the surrounding rock, it came at specific points that were dictated by the old relief below the Zechsteinablagerungen to first salt accumulations of which rise from the salt in the direction of earth's surface began ( Halokinese ).
• Latest from the Early Jurassic were made in what is now Central Europe crustal movements, which fell on the long-range effect of plate-tectonic processes and additionally favored the rise of salt since it weakened the outer layers. The salt preferably penetrated on or in these " weak zones " upwards. The top layers were curved upwards or pushed to the side. In the vicinity of salt domes in the salt migrated, however, and at the surface were formed about so-called edge sinks.
• By Subrosion may form as the top horizontal boundary surface of a salt dome of the so-called salt levels. In the absence of rainfall, it is possible that the salt several hundred meters high towering mountains forms (eg in the Zagros Mountains / Iran).

The example of Zechsteinsalze described here can be applied to the development of most salt domes ( geologically older and younger ). The below longitudinal section through the Northwest German Basin shows some salt domes whose root zone is located in the Zechstein.

Dissemination

Salt domes are most common phenomenon that occurs when the thickness of the salts and of the overlying sediments is sufficiently large to permit movement salt. In Central Europe they are mainly in the North German and Polish Lowland, and find very often in the Alps. They are mainly known if the top of the salt dome near enough to the surface or even pending without any overlap. The easily soluble salts ( halite ) were then dissolved in the upper regions, leaving only to find plaster.

Examples are:

• Lüneburg in Lower Saxony;
• Kalkberg in Bad Segeberg in Schleswig -Holstein;
• Sperenberg in Brandenburg;
• The salt dome Conow in Mecklenburg -Vorpommern;
• Inowroclaw ( Hohensalza ) in Poland;
• The Asse, a final repository for radioactive waste;
• Although the Gorleben salt dome does not reach the surface, a potential repository site for radioactive waste;
• Hallstatt salt mines, deposits of the Tethys Sea, mining since the early Iron Age ( Hallstatt culture)
• The salt dome in Abovyan in Armenia with use of natural gas as a strategic stock.

In dry climates, the exposed salt dome survive long periods without complete washout and even make salt glacier.