This articleneeds additional citations forverification. Please helpimprove this article byadding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Keuper" – news ·newspapers ·books ·scholar ·JSTOR(October 2010) (Learn how and when to remove this message)

TheKeuper is alithostratigraphic unit (a sequence ofrock strata) in thesubsurface of large parts of west and centralEurope. The Keuper consists ofdolomite,shales orclaystones andevaporites that were deposited during theMiddle andLate Triassicepochs (about220 million years ago). The Keuper lies on top of theMuschelkalk and under the predominantlyLower JurassicLias or other Early Jurassic strata.

The Keuper together with the Muschelkalk and theBuntsandstein form theGermanic Trias Group, a characteristic sequence of rock strata that gave theTriassic its name.^[2]

The Upper Triassic is well exposed inSwabia,Franconia,Alsace andLorraine andLuxembourg; it extends fromBasel on the east side of theRhine intoHanover, and throughEngland intoScotland and north-eastIreland; it appears flanking the central plateau ofFrance and in thePyrenees andSardinia.^[3] The Keuper sequence is linked by name to theKeuper Uplands area of southern Germany.

In southSweden, the lower portion containscoal-bearing strata, as in theHimalayas,Japan,Tibet,Burma, easternSiberia and inSpitsbergen. The upper portion of theKaroo Supergroup ofSouth Africa and part of theOtapiri stage ofNew Zealand are probably of Rhaetian age.^[3]

In Germany and adjacent parts of western and central Europe, the Keuper unit is divided into three groups:

• Upper Keuper

The upper part of this division is often a greydolomite known as theGrenz dolomite; the impurecoal beds Lettenkohle are aggregated towards the base. The upper Keuper, Rhaetic or Avicula contorta zone in Germany is mainly sandy with dark greyshales andmarls; it is seldom more than 25 m thick (82 ft). The sandstones are used for building purposes atBayreuth, Culmbach andBamberg. In Swabia and the Wesergebirge are severalbone-beds, thicker than those in the middle Keuper, which contain a rich assemblage of fossil remains of fish, reptiles and the mammalian teeth ofMicrolestes antiquus andTriglyptzas Fraasi. The name "Rhaetic" is derived from the Rhaetic Alps where the beds are well developed; they occur also in central France, the Pyrenees and England. In South Tirol and the Judicarian Mountains, the Rhaetic is represented by theKossenei beds. In the Alpine region, the presence of coral beds gives rise to the so-called Lithodendron Kalk.^[3]

• Hauptkeuper orGipskeuper, the middle

The middle division is thicker than either of the others (at Göttingen, 450 m, 1,480 ft); it consists of a marly series below, grey, red and green marls, withgypsum and dolomite—this is the gypskeuper in its restricted sense. The higher part of the series issandy, hence called the Steinmergel; it is comparatively free from gypsum. To this division belong theMyophoria beds (M. Raibliana) withgalena in places; theEstheria beds (E. laxilesta); the Schelfsandstein, used as a building-stone; theLehrherg andBerg-gyps beds;Semionotus beds (S. Bergen) with building-stone ofCoburg; and the BurgandStubensandstein.^[3]

• Kohlenkeuper, Unterkeuper orLettenkohle, the lower

The lower division consists mainly of greyclays andschieferletten with white, grey and brightly coloredsandstone and dolomiticlimestone.^[3]

Thesalt, which is associated with gypsum, is exploited in south Germany at Dreuze, Pettoncourt, as well as in Vie in theLorraine region of France. A 4-metre (13 ft) coal is found on this horizon in theOre Mountains on the border between Germany and theCzech Republic, and another, 2 metres thick (7 ft), has been mined inUpper Silesia, now inPoland.^[3]

In Great Britain the 'Keuper' is no longer a formally recognised geological division. The one-time Keuper Marls are now redesignated as theMercia Mudstone Group. The underlying Keuper Sandstone is now the Helsby Sandstone Formation at the top of theSherwood Sandstone Group.Traditionally it contained the following subdivisions:

• Rhaetic or Penarth

Grey, red and green marls, black shales, and so-called white (3.0–45.7 m, 10–150 ft). Upper Keuper marl, red and grey marls and shales with rock salt, 240–910 m (800–3,000 ft). As in Germany, there are one or more bone beds in the English Rhaetic with a similar assemblage of fossils.

• Lower Keuper

Sandstone, marls and thin sandstones at the top, red and white sandstones (including the so-called waterstones) below, withbreccias and conglomerates at the base, 46–76 m (150–250 ft).

• Basal conglomerate

A shore or scree breccia derived from local materials; it is well developed in theMendip district. The rocksalt beds vary from 25 cm (1 inch) to 30 metres (100 ft) in thickness; they are extensively worked (mined and pumped) inCheshire,Middlesbrough andCounty Antrim.^[3]

The Keuper covers a large area in theMidlands and around the flanks of thePennine range; it reaches southward to the eastDevon coast, northeastward intoYorkshire and northwestward into Northern Ireland and southernmost Scotland.^[3]

The Keuper is not rich infossils; the principal plants arecypresslikeconifers (Walchia,Voltzia) and a fewcalamites with such forms asEquisetum arenaceum andPterophyllum jaegeri.Avicula contorta,Protocardium rhaeticum,Terebratula gregaria,Myophoria costata,M. goldfassi,Lingula tenuessima, andAnoplophoria lettica may be mentioned among the invertebrates. The fish includeCeratodus,Hybodus andLepidotus.^[3]

Labyrinthodonts represented by the footprints ofCheirotherium and the bones ofMastodonsaurus (originally calledLabyrinthodon) andCapitosaurus. Among thereptiles areHyperodapedon,Palaeosaurus,Zanclodon,Nothosaurus,Henodus andBelodon.^[3] The first fossilmammals also make their appearance at this time and the earlybeetleTriamyxa is also known from the Keuper.

• Ogg, James G.; Ogg, Gabi M.; Gradstein, Felix M. (2016). "Triassic".A Concise Geologic Time Scale: 2016. Elsevier. pp. 133–149.ISBN 978-0-444-63771-0.
•  This article incorporates text from a publication now in thepublic domain: Howe, John Allen (1911). "Keuper". InChisholm, Hugh (ed.).Encyclopædia Britannica. Vol. 15 (11th ed.). Cambridge University Press. p. 766.

• Triassic System of Europe
• Lithostratigraphy
• Lithostratigraphy of Germany
• Stratigraphy of Europe

• Articles with short description
• Short description is different from Wikidata
• Articles needing additional references from October 2010
• All articles needing additional references
• Wikipedia articles incorporating a citation from the 1911 Encyclopaedia Britannica with Wikisource reference
• Wikipedia articles incorporating text from the 1911 Encyclopædia Britannica