Hallesche Marktplatz Fault

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The Hallesche Marktplatz Fault (also known as the Halle Fault or Hallesche Fault ) is a north-west-south-east trending north- east dipping tectonic main fault in central Germany , which separates the Merseburg plaice in the south-west from the Halle-Wittenberger plaice in the north-east, including the market square the city of Halle (Saale) crosses. There it runs between the town hall , the Handel monument and the market church . This is a unique situation for a large city in Germany.

geology

General

The northwest-southeast ( Hercynian ) strike of the fault suggests that it was already Variscan , i.e. in the Upper Carboniferous (approx. 300 million years ago). Plate tectonic events in the late Jurassic , with their peak in the Cretaceous more than 65 million years ago, led to a reactivation of the Hallesche Fault, among others. In the urban area of ​​Halle, the north-east plaice (Halle-Wittenberger plaice) was pushed back against the south-western plaice (Merseburger plaice, structurally part of the Thuringian basin ) by 600 m, locally by up to 1500 m. This did not happen suddenly, but rather over a period of approximately 30 million years, presumably associated with numerous earthquakes . Outside the urban area of ​​Halle, the fault merges both to the northwest and to the southeast into a fault zone ( staggered rupture ) that is up to several hundred meters wide in some cases , with the amount of offset also gradually decreasing with increasing distance from the city. In the Großkugel area it is only 20 m. Today there is no earthquake hazard from the fault.

The uplift of the Halle-Wittenberger floe northeast of the fault led to the erosive exposure of the red-lying period " porphyries " and molasse sediments of the Saale depression , which were once overlaid by Mesozoic layers , but which are now largely covered by thin Cenozoic sediments.

The Merseburg plaice south-east of the fault was not lifted as much or not at all relative to the north-east and was therefore far less affected by erosion . Mesozoic rocks of the red sandstone and shell limestone ( Triassic ) are therefore preserved here, but are also largely below the thin Cenozoic sediments .

Brine springs

The layers of the Merseburg plaice are brought in near the fault. That is, they are bent upward by the movement on the perturbation surface. As a result, the layers of the Zechstein series , which are actually several hundred meters deep under the Mesozoic era of the Merseburg plaice, bite out in a narrow strip on the surface of the earth. In the urban area of ​​Halle, on and near the surface, they consist of a very crumbly residual rock , a dolomite grus , which on the one hand results from the tectonic stress at the fault and on the other hand from the leaching of a large part of the mostly relatively easily water-soluble sedimentary rocks of the Zechstein series through seeping in surface water emerged. In the depths and to the southwest, with increasing distance from the fault, they merge into solid dolomite and anhydrite or gypsum rock and rock salt .

Since parts of the Zechstein layers consist of very easily soluble rock salt, the deep groundwater that circulates in these layers is very salty ( brine ). In contrast to gypsum, the significantly more porous and water-permeable (more permeable) Zechstein dolomite acts as the main conductor for the brine and guides it up to the fault, where it penetrates just below the surface of the earth in the urban area of ​​Halle at the outcrop of the Zechstein.

Location and course within the city

The districts of Neustadt , Südstadt and Silberhöhe are located on the Merseburger Scholle . The Paulus and Mühlweg districts, large parts of the old town and Halle-Ost are located on the Halle-Wittenberger Scholle. In the city center, the fault runs across the market square. The slightly crooked western pair of towers of the St. Mary's Market Church is attributed to difficult foundation conditions, as the soil conditions differ as a result of the fault.

Significance for urban development

The Hallesche Fault has the greatest significance for the city in terms of the special geological situation that it created in the city area and that led to the formation of the brine springs . The four oldest, historically verifiable brine wells (Gutjahr-, Meteritz- and Hackeborn as well as Deutscher Born) are or were all in today's city center near the fault. The production of salt in the salt pans was of considerable economic importance, especially in the Middle Ages, when salt was balanced with gold, and is considered to be the origin of the city's name (see also →  History of the salt works in Halle ).

Visit with a geoscope

West side of the market square at the exit to the street An der Marienkirche , with the gold brine fountain on the left and the geoscope on the right (in front of the church)

As part of the market square renovation by 2006, a "geoscope" was created on the west side of the square near the market church . It is a stainless steel box over a shaft several meters deep. Interested passers-by can observe the course of the fault over a length of several meters underground through the glass lid of the box. The geoscope is located in the immediate vicinity of the gold brine fountain , a water feature that was also inaugurated in 2006 and symbolizes the once important brine springs.

swell

  • Holger Brülls, Thomas Dietzsch: Architectural Guide Halle on the Saale . Dietrich Reimer Verlag, Berlin 2000, ISBN 3-496-01202-1 .
  • Dietrich Franke: Regional Geology East. Geological online reference work for East Germany with around 2500-page encyclopedia (PDF; 19 MB) and separately downloadable maps and tables, etc. a. with a map of the tectonic structure of the Halle-Wittenberg floe (PDF; 470 kB).
  • A. Kampe, J. Luge, M. Schwab: The storage conditions in the northern border of the Löbejün porphyry near Halle (Saale) . In: Geology. Vol. 14, No. 1, 1965, pp. 26-46, ISSN  0046-5747 .
  • Manfred Frühauf: Natural favorable factors for the location and development of Halle in the mirror image of geological witnesses. In: Klaus Friedrich, Manfred Frühauf (Ed.): Halle and its surrounding area. Geographic excursion guide . 2nd edition, Mitteldeutscher Verlag, Halle 2006, ISBN 3-89812-167-4 , pp. 18–33.
  • The Halle fault and geology, soils and groundwater in: Environmental Atlas Halle (Saale) V2.0 .
  • Rediscover Halle on the geological nature trail - The Halle Market Square Fault. Leaflet, published by the city of Halle (Saale), 2006 ( online at halle.de )