Bayan Shireh Formation

Bayan Shireh Formation is a geological layer in eastern Gobi Desert, Mongolia, composed of grey mudstones and yellowish-brown sandstones. These rocks reach depths of 300 meters and divide into upper and lower sections, each with distinct rock compositions.

The formation was first documented in 1959 with sediments dating between 102 and 86 million years ago during the Late Cretaceous. This timeframe marks important geological shifts in the eastern Gobi region.

Researchers from multiple countries conduct expeditions to study the formation's diverse fossil collection, which includes therizinosaurs, turtles, and hadrosauroids.

Access to the formation depends on desert conditions and requires a local guide for safe exploration. The best time to visit is during dry spring or autumn when temperatures are moderate.

The layers contain fossils of therizosaurs, turtles, and hadrosaurids from when large water bodies and semi-arid conditions existed in the region. These discoveries reveal that the Gobi Desert was once a diverse ecosystem.