Middle Keuper

The Mean keuper (also means keuper, z. T. Gipskeuper , main keuper u. A.) Is a lithostratigraphic subgroup of Keupers of Germanic Trias . The lithostratigraphic unit is underlain by the Erfurt Formation and in the eastern edge areas by the Grafenwoehr Formation of the Lower Keuper and overlaid by the subgroup of the Upper Keuper . The middle Keuper contains z. Sometimes very thick evaporites , in the higher part almost exclusively continental deposits.

definition

The lower limit is defined in francs with the upper edge of the border dolomite . The upper limit is the base of the "Rhaet" sandstone; in northern Germany the postera sandstones, in southern Germany, where there are no postera sandstones, the contorta sandstones.

Biostratigraphically, the lower limit of the Middle Keuper is dated to the upper Ladinium (Upper Langobardian). The border between the middle and the upper Keuper is already in the Lower Rhaetium (Sevatium lower level). Geochronologically, this corresponds roughly to the period from 232.5 to 209 million years. However, more than half of the time is not documented by deposits, but is in several layer gaps and erosion discordances within the Middle Keuper. The type region of the Middle Keuper is Franconia; a type profile has not yet been defined.

The lithology is extremely variable. The z. Sometimes very powerful saline results with rock salt , anhydrite and gypsum as well as the colorful clay and marl stones stored between them . There are also clastic sand, silt and clay stones. The average thickness of the Middle Keuper in northern Germany is 250 to 400 m. In trenches, up to 1000 m can be reached locally. In the Glückstadt-Graben, up to 5000 m in thickness are assumed. In threshold areas, the Middle Keuper can be almost completely eroded as a result of the ancient Kimmerian movement. In southern Germany, thicknesses of up to about 350 m are reached, but they decrease to 0 m towards the eastern edge of the basin.

The debris came from the edges of the basin; in northern Germany from the Fennoskandische Schild , in southern Germany from the Vindelizisches Land , in the west from the Ardennes massif.

structure

The breakdown into formations in northern and southern Germany is different. In northern Germany a distinction is made (from top to bottom):

In southern Germany, the lithostratigraphic classification was slightly changed and adapted to the local lithological sequence (from top to bottom).

However, these formations do not all lie on top of one another, but rather interlock laterally. The Grabfeld Formation roughly corresponds to the Gipskeuper in southern Germany and interlocks laterally with the Benk Formation towards the Vindelizisches Land. The Stuttgart formation corresponds roughly to the "reed sandstone". The Weser Formation of Northern Germany is equated with the Mainhardt, Hassberge and Steigerwald Formation and corresponds roughly to the "Bunten Margeln", "Oberen Gipskeuper" or "Unterer Steinmergelkeuper", whereby the Hassberge Formation is the edge facies of the Vindelizisches Land forms. The Arnstadt formation essentially corresponds to the “stone marlkeuper”, the Löwenstein formation roughly to the “Stubensandstein” or “Burgsandstein”, and the Trossingen formation roughly to the earlier term “tuber marl”.

Storage room

The rocks of the Middle Keuper were deposited in a wide, shallow basin. At least in the lower part, there were also brief marine advances into the basin. In the Grabfeld formation, locally powerful evaporites were deposited, which were formed in large continental salt lakes. Presumably, however, there was also marine influence here. In the Stuttgart formation, a wide river system from the Fennoskandische Schild built into the basin. In the higher part of the Middle Keuper, this pouring was limited to the northern part of the Germanic Basin. There was pouring from the Vindelizisches Land , the Bohemian Land , the Ardennes massif and, for a short time, the Rhenish massif .

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
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

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)