Trossingen formation

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Lithostratigraphy by the Keuper group in the Germanic Basin
Boundary information between the exterior formation in the hanging wall and the Trossingen formation in the lying area near Hechingen-Stein
Marl meadow near Leinzell

The Trossingen Formation (formerly also known as tuber marl or Feuerletten ) is a lithostratigraphic unit of formation rank . It belongs to the Keuper group of the Germanic Triassic . The Trossingen Formation is underlain by the Löwenstein Formation and erosively overlaid by the Exter Formation , partly also directly by the Black Jura .

definition

The lying boundary of the Trossingen Formation is a diachronic facies boundary and is expressed by the exposure of the sandstones of the Löwenstein Formation . The slope boundary is also sharply formed and characterized by the erosive overlay of terrestrial sediments of various locally distributed strata of the Exter Formation (Malschenberg clay or sandstone, Contorta clay, Tübingen sandstone) or, in the case of a more extensive Oberkeuper hiatus, directly with it the dark marine claystones of the Black Jura .

The Trossingen formation itself consists of fairly uniform, red-brown to red, sometimes purple clay stones, in which lime tuber layers occasionally intervene (hence the name "tuber marl"). In northern Franconia there can also be continuous limestone crusts several meters thick. At the top of the episode, carbonaceous clay stones and silicified limestone also occur locally.

The Trossingen formation is limited to the edge of the Vindelizian threshold and thus to the southern German layer level country . The thickness averages around 40 to 50 m, in northern Franconia values ​​between 55 and 60 m are reached. In southern Württemberg (Wutach area) the thickness decreases to 10 m. The differences in thickness go back on the one hand to the interlocking with the Löwenstein Formation and on the other hand to the Rhaetian / early Jurassic erosion.

Chronostratigraphically , the Trossingen formation is placed in the uppermost norium or lower rhaetium (upper Upper Triassic ). The type locality or type profile is the impact slope of the Trosselbach near Trossingen ( Tuttlingen district ). It was named after the city of Trossingen. The type region is southwestern Baden-Württemberg.

structure

The Trossingen formation has not yet been subdivided.

Storage room

The deposit area was a wide, shallow basin with a warm climate, in which lakes and swamps spread, which largely dried out during periods of low rainfall. Widespread soil formations (root horizons, lime lumps and crusts ) indicate longer interruptions in the sedimentation. The top of the formation was already deposited under marine influence, as evidence of foraminifera shows .

Fossils

The Trossingen formation has become world-famous thanks to the " Plateosaur cemetery" in Trossingen. The well-preserved skeletons are z. Partly assembled in the Natural History Museum Stuttgart in the Museum am Löwentor , and exhibited in the Museum Auberlehaus in Trossingen. Trossinger plateosaurs can also be found in the museums of Tübingen and New York (USA).

In addition to the plateosaurs, it is above all the well-preserved fossils of the "ancient tortoise" Proganochelys quenstedti that established the paleontological importance of the Trossingen dinosaur cemetery .

Other, less spectacular fossil finds in the Trossingen Formation are mussels (Bivalvia) and mussel crabs (Ostracoda). Foraminifera are already showing marine influence at the top of the formation .

Geomorphology and economic importance

The outcrops of the Trossingen formation (tuber marl) are characterized by so-called "humpbacked" meadows. The marl forms very heavy soils ( minute soil ), which are recognizable by typical tree growth (crooked and crooked trees), and tends to frequent landslides after rainfall. Often, marl landscapes can only be used for orchards .

Due to its richness in claystone, the marl, like the many Keuper formations, is a difficult subsoil for buildings of any kind, because the claystones contain three-layer clay minerals, which can swell due to water retention in the intermediate layers. Even intensive arable farming is therefore problematic due to the very weather- dependent processing options.

The marl, like many claystone-dominated rock sequences, tends to creep on slopes. This is expressed in the fact that trees on slopes show so-called "saber growth".

literature

  • Gerhard Beutler: Lithostratigraphy. In: German Stratigraphic Commission (Ed.): Stratigraphie von Deutschland IV - Keuper. Courier Forschungsinstitut Senckenberg, 253: 65-84, Stuttgart 2005. ISSN  0341-4116
  • Gerhard Beutler, Norbert Hauschke and Edgar Nitsch: Facies development of the Keuper in the Germanic Basin. In: Norbert Hauschke & Volker Wilde (eds.): Trias - A whole other world. Central Europe in the early Middle Ages. Pp. 129–174, Verlag Dr. Friedrich Pfeil, Munich 1999. ISBN 3-931516-55-5
  • Edgar Nitsch: The Keuper in the Stratigraphic Table of Germany 2002: Formations and consequences. Newsletters on Stratigraphy, 41 (1-3): 159-171, Stuttgart 2005. ISSN  0078-0421
  • Eduard Mückenhausen: Soil science and its geological, geomorphological, mineralogical and petrological basis. 4th supplementary edition, 579 pages, DLG-Verlag, Frankfurt / M. 1993. ISBN 3-7690-0511-2
  • Ernst Schlichting: Introduction to Soil Science . 3rd ed., 131 S, Parey, Hamburg & Berlin, 1993. ISBN 3-490-20115-9

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