Upper Keuper
The upper keuper (also upper keuper , Rhätkeuper , Rätkeuper or Rhätsandstein ) is a lithostratigraphic subgroup of Keupers of Germanic Trias . It currently only includes one formation, the Exter formation . The lithostratigraphic unit is underlain by the Middle Keuper subgroup and overlaid by the Lias in the North German Basin and the Black Jura in the South German Basin .
definition
The lower limit of the Upper Keuper is the base of the so-called postera sandstones in northern Germany . However, it is strongly diachronic, i.e. H. different ages. In southern Germany, the Obere Keuper begins with the base of the contorta sandstone, as no postera sandstone has been developed here. The upper limit is also likely to be of different ages. It lies at the base of the Lias or the Black Jura, in southern Germany thus at the base of the Psilonotenton formation . The Upper Keuper consists almost exclusively of clastic clay , silt and sandstones . Occasionally there are also carbonates and root soils with thin carbonaceous layers. The thicknesses in northern Germany are on average between 100 m and 150 m; locally they can rise to over 250 m. In southern Germany, the unit is consistently less thick, a maximum of about 45 m. The unit quickly wedges in the southern edge of the Vindelician country . Biostratigraphically , the Upper Keuper begins in the lower Rhaetium (Sevatium) and ends shortly before the Triassic-Jura border. The type region is the Weserbergland . The type profile is in the Exter valley and consists of several sub-profiles.
structure
Currently the Obere Keuper only includes one formation, the Exter formation. Traditionally, the Obere Keuper is subdivided into three units, which in the future can get the rank of subformations. On the basis of older names, Beutler suggests a subdivision into three sub-formations (from top to bottom):
- Vahlbruch subformation (Triletes layers or Upper Rhine)
- Oeynhausen subformation ( contorta layers or Mittelrhät)
- Rinteln subformation ( postera layers or Unterrhät)
Storage room
The rocks of the Upper Keuper were sedimented in a wide delta. Fine-grained sediments were deposited in the flood plains between the river arms. There was also soil formation with carbonate or iron crusts. Organic matter was enriched in large swamps and thin coal seams were formed . The sandstones were deposited in river channels, which in northern Germany mainly came from the Fennoskandische Schild . In southern Germany, however, debris from the Bohemian and Vindelizian Lands and in the west from the Ardennes mainland are known.
Fossils
The Upper Keuper is not particularly rich in fossils. In the lower part a species-poor mussel fauna with Unionites postera , the eponymous species of the postera layers, was found. Also are often ostracods (ostracods) that have a certain stratigraphic value partly and spores and [pollen] of land plants. In the middle part shells were (with the contorta layers eponymous kind Rhaetavicula contorta ,) snails , brachiopods and ostracods (ostracods) and foraminifera found. In the upper part only plant remains (including spores and pollen) and rarely mussel crabs and foraminifera appear. The triletes layers are named after the spore genus Triletes .
Use of geothermal energy in the North German Plain
The Keuper and the Rätkeuper are the strata of the earth that are visited in Neustadt-Glewe at a depth of 2,455 meters from which the thermal water is extracted for the Neustadt-Glewe geothermal power plant , Germany's first geothermal power plant . The salt content of the brine is 220 grams per liter.
Individual evidence
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)