Grabfeld formation

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Lithostratigraphy by the Keuper group in the Germanic Basin

The Grabfeld Formation (older terms are Gipskeuper or Unterer Gipskeuper and Salzkeuper) is a lithostratigraphic formation of the Middle Keuper in the Germanic Triassic . The lithostratigraphic unit is underlain by the Erfurt and Grafenwöhr Formation and overlaid by the Stuttgart Formation . In the outskirts to the Vindelizisches Land it interlocks with the Benk formation .

definition

The lower limit of the Grabfeld Formation is the upper edge of the border dolomite in northern and southern Germany . The upper limit is the discordance area of the Stuttgart formation . The Grabfeld Formation is typically made up of cyclic deposits of clay stones and evaporites . The colorful clay stones, dolomitic marl stones and embedded gypsum lumps are characteristic. In the basin centers in northern Germany, five rock salt deposits were identified by drilling. The thickness averages around 150 to 200 m, in trench zones 300 to 400 m are also reached. In the Glückstadt-Graben, values ​​of over 2000 m thickness are reached, in threshold areas, however, it is often only 90 m. In southern Germany, the thickness varies from 140 m to 0 m at the basin edges towards the Vindelizisches Land. The grave field formation is dated to the Ladinium (upper Langobardian lower stage) to Carnian ( Cordevolium lower stage). In geochronology, this corresponds to the period from about 232.5 to 229 million years. The type locality of the Grabfeld formation is in Grabfeld , a landscape in the Franconian-Thuringian border area. The type profile is a borehole near Heldburg .

structure

Gypsum quarry on the Äulesberg near Vellberg :
base gypsum , Bochinger horizon, dark red marl, galena bank and middle gypsum horizon

The Grabfeld formation has not yet been subdivided into subformations. However, a subformation breakdown is already in use in northern Germany, the use of which is already recommended:

  • Bredenborn subformation
  • Oldenburg subformation
  • Vogelsang subformation
  • Hummersen subformation
  • Mönchsberg subformation
  • Vörden subformation
  • Elbrinxen subformation
  • Löwendorf subformation

The Grabfeld formation can be divided into eight small cycles.

Storage room

In the central part of the basin , the Grabfeld Formation contains mighty evaporites that were formed in large continental salt lakes. However, marine influence is also discussed. In northern Germany, rock salt was deposited in five cycles, anhydrite in the more peripheral areas . It is possible that the original distribution of rock salt has been greatly reduced due to deep leaching.

Fossils

The Grabfeld Formation is extremely poor in fossils; the fossil tour is limited to the dolomitic marl stones, which occasionally lead to mussels . Mussel shells (Conchostraca) and fish remains were also found.

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 (Hrsg.): Trias - A whole different world of 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

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