Weser formation

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Lithostratigraphy by the Keuper group in the Germanic Basin

The Weser Formation (formerly also Oberer Gipskeuper , Bunte Mergel or Rote Wand) is a lithostratigraphic formation of the Middle Keuper in the Germanic Triassic . The lithostratigraphic unit is underlain by the Stuttgart Formation and overlaid by the Arnstadt Formation .

definition

The lower limit of the Weser Formation is the base of the so-called main stone marl or the Beaumont horizon or the Kühlsche breccia. The upper limit is the upper edge of the Heldburg plaster marl. The Weser formation consists mainly of clay stones and evaporites . In the lower part of the formation contains red-brown clay stones with sulphate layers ("red wall"). Greenish and colored mudstones with stone marl banks ("Lehrbergbänke") follow. In the rock salt deposit areas, three rock salt deposits have been identified. The thicknesses are on average around 100 to 150 m, in trench zones over 400 m are also reached. However, the thicknesses can be greatly reduced due to salt and gypsum leaching. In southern Germany only 75 m to less than 10 m are reached. At the edge of the basin towards the Vindelizisches Land, the Weser Formation meshes with the Steigerwald , Hassberge and Mainhardt Formations . The Weser formation is dated to the Carnian (lower stages Julium to Tuvalium ). According to the STD2002, this corresponds geochronologically to a period of 3.5 million years (224.5 to 221 mya). The type locality of the Weser formation is near Polle on the Weser. The type region is the Weserbergland.

structure

The division of the Weser formation into subformations has not yet been officially decided. In 2005 Vath proposed the following subdivision for the Weser formation in southern Lower Saxony:

  • Polle subformation
  • Rischenau subformation

Up to 11 small sedimentary cycles can be distinguished.

Storage room

The deposit area of ​​the Weser Formation was very similar to the deposit area of ​​the Grabfeld Formation . Mudstone was deposited in a wide and shallow basin. Brief flooding and drying out resulted in the deposition of evaporites. In the remaining lakes (salt lakes), up to several hundred meters of rock salt was deposited.

Fossils

The Weser Formation contains only a few fossils. The Lehrberg banks lead mussels (Bivalvia), snails (Gastropoda) and ostracods (Ostracoda). Some vertebrates have also been 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
  • Ulrich Vath: The Keuper in southern Lower Saxony near Göttingen. In: German Stratigraphic Commission (Ed.): Stratigraphie von Deutschland IV - Keuper. Courier Forschungsinstitut Senckenberg, 253: 163-178, Stuttgart 2005 ISSN  0341-4116

Web links

  • German Stratigraphic Commission (Ed.): Stratigraphische Tisch von Deutschland 2002 . Potsdam 2002, ISBN 3-00-010197-7 - PDF; 6.57 MB (large) (abbreviated STD2002)