Norian
The Norian ( Nor) is in the geologic timescale, middle stage of the Upper Triassic, the geochronological corresponds to the period before about 228 to about 208 500 000 years, which is about 19.5 million years lasted. The previous stage is the Carnian, the subsequent stage the Rhaetian.
Naming and history
The original type locality is in the Noric Alps ( Austria ), from which the name for the stage. Edmund of Mojsisovics suggested level and name in 1869.
Definition and GSSP
The beginning of the stage is defined primitius through the base of ammonite zone Klamathites macrolobatus or Stikinoceras kerri and by the conodont zones Metapolygnathus communisti or Metapolygnathus. The end of the stage, the first appearance of the ammonite species Cochloceras amoenum was defined. In addition occur near the base of the conodont Misikella spp. and Epigondolella mosheri first time, as well as the radiolarian species Proparvicingula moniliformis. An official GSSP (global valid type locality and type profile ) has not yet been adopted.
Subdivision
The Norian is subdivided in Tethysbereich in six ammonite zones:
- Halorites macer - zone
- Himavatites hogarti zone
- Cyrtopleurites bicrenatus zone
- Juvavites magnus Zone
- Malayites paulckei zone
- Guembelites jandianus zone
Regionally, the Norian is in the lower grades Lacium (Lac ) divided Alaunium ( alum) and Sevatium ( Sevat ).