Dyas (geology)

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Dyas - Permian of Central Europe
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The Dyas (the two-part, after the subdivision into Rotliegend and Zechstein) was the name coined in Central Europe for the uppermost geological period of the Paleozoic, which however could not assert itself internationally. Today it is largely taken from the internationally used Permian system . Since the term Dyas was primarily defined by marked changes in the rock sequence, it is used today as a name for a lithostratigraphic supergroup (or main group ) in Central Europe, which includes Rotliegend and Zechstein . The boundaries are mostly diachronous , i.e. H. The Dyas rock sequence does not begin simultaneously everywhere in Central Europe, nor is it present everywhere (or was present before the later erosion). In some threshold regions , Unterer Buntsandstein can lie directly on the prepermic subsoil. The Dyas can start locally as early as the Upper Carboniferous ( Gzhelium ) and ends around 100,000 years before the internationally valid Permian / Triassic border in the upper Changhsingian . The (earlier) equation of Rotliegend with the (earlier) Unterperm and Zechstein with the (earlier) Oberperm is also no longer permissible, as the almost isochronous lower limit of the Zechstein is already within the Wuchiapingium .

history

In 1859 Jules Marcou summarized the rock units that were previously known as Rotliegend and Zechstein under the name Dyas. In 1861 he was followed by Hanns Bruno Geinitz and also adopted the term for the German-speaking area. In 1841 Roderick Murchison had already eliminated the Permian system. Since the division of the Permian into two parts of the world and regions could not be traced, the term Perm finally prevailed for this section of the earth's history.

definition

The lower limit of the Dyas and the Rotliegend has not yet been formally defined; however, according to what we know so far, it is strongly diachronous . In the Saar-Nahe basin , the lower limit lies at the base of the Remigiusberg formation . In the Wetterau it is placed at the base of the Lindheim formation . In the Thuringian Forest it has not yet been decided whether it should be placed at the base of the Georgenthal / Möhrenbach formation or at the base of the Ilmenau formation . In the northern valley of the Saale, the base of the Halle formation , the lower limit, forms the base of the Süplingen formation on the Flechtlinger Scholle . In the Vorerzgebirge the lower limit is at the base of the Härtensdorf formation , in the Döhlen basin at the base of the Unkersdorf formation and in northern Germany mostly at the base of the volcanic complexes.

The upper limit of the Dyas was set by a resolution of the German Union of Geological Sciences (DUGW) at the top of the so-called "crumbling slate". As a result, another saline was found in the North Sea in 2000. The result is now the uppermost section of the Zechstein as a result z7.

The rock unit of the Dyas in the lower part (= Rotliegend) contains terrestrial, fluvial, lacustrine, aeolian and volcanogenic sediments, coarse conglomerates, breccias and sandstones as well as fine-grained clays, evaporites and limes. Mighty igneous rocks are also used locally (lavas, pyroclastics, ignimbrites, less often sub-volcanic bodies). These deposits are predominantly colored red. In the upper part (= Zechstein), mighty evaporites, limes, dolomites and clays dominate, and clastic sediments are rare. The sediments are usually light or gray in color. The Dyas reaches cumulative thicknesses of up to 5,000 m. However, the centers of sedimentation shifted during the deposition of the dyas, so that at no point do 5,000 m of sediments actually lie on top of each other. The type region of the Dyas is Central and Western Europe. It begins regionally already in the Gzhelium , the highest chronostratigraphic level of the international subsystem of the Pennsylvania (formerly partly "Upper Carbon") and extends to the upper Changhsingian , the upper chronostratigraphic level of the international Upper Perm ( Lopingium ). In areas where the red sandstone sets in very early, the Dyas ends around 100,000 years before the international Permian / Triassic border. Expressed in absolute terms, the Dyas covers a period of almost 50 million years, from around 302 to 251 million years.

Breakdown

The Dyas supergroup or Dyas main group is now divided into two lithostratigraphic groups

There used to be a subdivision into

The terms were often used synonymously. From today's point of view, this was a rather unfortunate combination, because the ending -ium for Autunium, Saxonium and Thuringium implies a geochronological or chronostratigraphic unit of time, while Rotliegend and Zechstein are purely lithostratigraphic terms. However, z. Sometimes the terms Autunium, Saxonium and Thuringium have been used or defined quite differently from author to author, i.e. H. the three levels were far from being useful regional levels in the past. Manfred Menning and Jürgen Boy (in Menning et al., 2005) advise against using these terms today. However, they are of great historical interest because they are widely used in the older literature.

swell

Individual evidence

  1. Spencer G. Lucas, Joerg W. Schneider and Giuseppe Cassinis: Non-marine Permian biostratigraphy and biochronology: an introduction. In: Spencer G. Lucas, Giuseppe Cassinis and Joerg W. Schneider (Eds.): Non-Marine Permian Biostratigraphy and Biochronology. Geological Society, London, Special Publications, 265, 1-14, London 2006 PDF

literature

  • Manfred Menning, Reinhard Benek, Jürgen Boy, Bodo-Carlo Ehling, Frank Fischer, Birgit Gaitzsch, Reinhard Gast, Gotthard Kowalczyk, Harald Lützner, Wolfgang Reichel and Jörg W. Schneider: Das Rotliegend in the Stratigraphic Table of Germany 2002 - "Paternoster- Stratigraphy "on the decline. Newsletters on Stratigraphy, 41 (1-3): 91-122, Stuttgart 2005 ISSN  0078-0421
  • Karl-Christian Käding: The Zechstein in the Stratigraphic Table of Germany 2002. Newsletters on Stratigraphy, 41 (1-3): 123-127, Stuttgart 2005 ISSN  0078-0421
  • Manfred Menning, Reinhard Gast, Hans Hagdorn, Karl-Christian Käding, Theo Simon, Michael Szurlies and Edgar Nitsch: time scale for Permian and Triassic in the Stratigraphic Table of Germany 2002, cyclostratigraphic calibration of the higher Dyas and Germanic Triassic and the age of the Roadium stages to Rhaetium 2005. Newsletters on Stratigraphy, 41 (1-3): 173-210, Stuttgart 2005 ISSN  0078-0421

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