The Exter Formation is the only formation of the Upper Keuper or Rhätsandstein, and is a geologic formation in Germany. It preserves fossils dating back to the Rhaetian of the Triassic period.
Exter Formation at Krauthausen
The Rhaetian is the latest age of the Triassic Period or the uppermost stage of the Triassic System. It was preceded by the Norian and succeeded by the Hettangian. The base of the Rhaetian lacks a formal GSSP, though candidate sections include Steinbergkogel in Austria and Pignola-Abriola in Italy. The end of the Rhaetian is more well-defined. According to the current ICS system, the Rhaetian ended 201.4 ± 0.2 Ma.
Hüsing et al. (2011) argued that the Rhaetian extended for almost 10 million years based on biomagnetostratigraphy at Steinbergkogel, a candidate GSSP near Hallstatt, Austria
Wotzlaw et al. (2014) radiometrically dated the Norian-Rhaetian boundary to ~205.50 Ma based on the extinction of Monotis in Peru