Keuper


The Keuper is a lithostratigraphic unit in the subsurface of large parts of west and central Europe. The Keuper consists of dolomite, shales or claystones and evaporites that were deposited during the Middle and Late Triassic epochs. The Keuper lies on top of the Muschelkalk and under the predominantly Lower Jurassic Lias or other Early Jurassic strata.
The Keuper together with the Muschelkalk and the Buntsandstein form the Germanic Trias Group, a characteristic sequence of rock strata that gave the Triassic its name.

Exposure

The Upper Triassic is well exposed in Swabia, Franconia, Alsace and Lorraine and Luxembourg; it extends from Basel on the east side of the Rhine into Hanover, and through England into Scotland and north-east Ireland; it appears flanking the central plateau of France and in the Pyrenees and Sardinia. The Keuper sequence is linked by name to the Keuper Uplands area of southern Germany.
In south Sweden, the lower portion contains coal-bearing strata, as in the Himalayas, Japan, Tibet, Burma, eastern Siberia and in Spitsbergen. The upper portion of the Karoo Supergroup of South Africa and part of the Otapiri stage of New Zealand are probably of Rhaetian age.

Germany

In Germany and adjacent parts of western and central Europe, the Keuper unit is divided into three groups:
  • Upper Keuper
  • Hauptkeuper or Gipskeuper, the middle
  • Kohlenkeuper, Unterkeuper or Lettenkohle, the lower
The salt, which is associated with gypsum, is exploited in south Germany at Dreuze, Pettoncourt, as well as in Vie in the Lorraine region of France. A 4-metre coal is found on this horizon in the Ore Mountains on the border between Germany and the Czech Republic, and another, 2 metres thick, has been mined in Upper Silesia, now in Poland.

Great Britain

In Great Britain the 'Keuper' is no longer a formally recognised geological division. The one-time Keuper Marls are now redesignated as the Mercia Mudstone Group. The underlying Keuper Sandstone is now the Helsby Sandstone Formation at the top of the Sherwood Sandstone Group.
Traditionally it contained the following subdivisions:
  • Rhaetic or Penarth
  • Lower Keuper
  • Basal conglomerate
The Keuper covers a large area in the Midlands and around the flanks of the Pennine range; it reaches southward to the east Devon coast, northeastward into Yorkshire and northwestward into Northern Ireland and southernmost Scotland.

Fossils

The Keuper is not rich in fossils; the principal plants are cypresslike conifers and a few calamites with such forms as Equisetum arenaceum and Pterophyllum jaegeri. Avicula contorta, Protocardium rhaeticum, Terebratula gregaria, Myophoria costata, M. goldfassi, Lingula tenuessima, and Anoplophoria lettica may be mentioned among the invertebrates. The fish include Ceratodus, Hybodus and Lepidotus.
Labyrinthodonts represented by the footprints of Cheirotherium and the bones of Mastodonsaurus and Capitosaurus. Among the reptiles are Hyperodapedon, Palaeosaurus, Zanclodon, Nothosaurus, Henodus and Belodon. The first fossil mammals also make their appearance at this time and the early beetle Triamyxa is also known from the Keuper.