Nemegt Formation

The Nemegt Formation is a Late Cretaceous rock unit in the Gobi Desert of Mongolia, spread across Bayankhongor, Omnogovi and Ovorkhangai provinces, dating to the Maastrichtian age and possibly extending into the late Campanian, with deposition occurring before roughly 66.7 million years ago. It consists mainly of mudstones and sandstones, with secondary conglomerate, deposited by ancient rivers, lakes and floodplains under a seasonally wet and dry climate; its upper sections preserve evidence of braided river meanders and oxbow lakes, while siltstone pellets record repeated desiccation at channel margins. The formation contains fossils of fish, turtles, crocodilians and a diverse assemblage of dinosaurs, including birds.