Rhaetian

The Rhaetian ( Rhät, also Advises ) is an internationally recognized geological stage of the Upper Triassic, which covers the period before about 208.5 to 201.3 million years ago and thus about 7.2 million years lasted. The Rhaetian is the last ( most recent) stage of the Triassic and following the Norian. On the Rhaetian the Hettangian follows.

Naming and history

The Rhaetian is named after the Rhaetian Alps ( old spelling Rhaetian Alps) in Eastern Switzerland and the adjoining border area of Italy and Austria. It was proposed by Albert Oppel and Eduard Suess in 1856.

Definition and GSSP

The base of the Rhaetian is not yet clearly defined; the lowest (first) ammonite zone of Rhaetiums is Tethysbereich Sagenites reticulatus. In the boreal region of this ammonite does not occur. Here the zone of Cochloceras is amoenum the lowest ammonite zone of Rhaetiums. In addition occur near the base of the conodont Misikella spp. and Epigondolella mosheri first time, as well as the radiolarian species Proparvicingula moniliformis. The upper limit is also uncertain, as the GSSP for the beginning of the Jurassic has not been conclusively defined. The uppermost ammonite zone of the Rhaetian is in the Tethys area marshi the zone of Choristoceras. However, there is up to the base of the well-defined Psiloceras planorbis zone of the Hettangian ( Lower Jurassic ), a transition region (so-called " praeplanorbis layers "), which can be further subdivided probably. In this transition region probably Trias-/Jura-Grenze will be defined.

Subdivision of the Rhaetian

The Rhaetian is subdivided in Tethysbereich in two ammonite zones.

• Choristoceras marshi zone
• Rhabdoceras suesii zone