Bayanshiree Formation

The Bayanshiree Formation is primarily composed by varicoloured claystones and sandstones with calcareous concretions and characterized by grey mudstones and yellowish-brown medium grained sandstones. Up to thick, the most complete sections are found in the eastern Gobi Desert, consisting of fine-grained, often cross-stratified gray sandstone interbedded with claystone and concretionary, intraformational conglomerates with relatively thick units of red to brown mudstone in the upper part. The Baynshire and Burkhant localities are mainly composed by mudstone, siltstone, sandstone, and conglomerates, with most of their sedimentation being fluvial. largescale cross-stratification in many of the sandstone layers at the Baynshire locality seem to indicate that a large meandering fluvial system was present. It has been implied that during the late Bayan Shirehnian times, large rivers with direct connections to the sea drained a prominent part of the eastern Gobi region. Stratigraphy According to Jerzykiewicz and Russell, the Bayanshiree Formation can be divided into 2 informal units: upper and lower beds. While the lower beds are composed by extensive conglomerate that indicates the ancient presence of very active rivers, the upper beds are mainly composed by mudstone and claystone that is interbedded by sandstone, indicating again, the presence of rivers but also lakes and other water bodies. However, examination of the magnetostratigraphy of the formation indicates that the entire Bayanshiree lies within the Cretaceous Long Normal, which lasted only until the end of the Santonian stage, giving a possible Cenomanian through Late Santonian age, between 98 and 83 million years ago. Correlations A potential correlation between the Iren Dabasu Formation has been long suggested by most authors, mainly based on the highly similar vertebrate assemblages. However, Van Itterbeeck et al. 2005 argued against this correlation concluding that instead, the Iren Dabasu Formation was coeval with the younger Nemegt Formation based on the charophyte and ostracode assemblages; therefore, these formations were dated to the Late Campanian-Early Maastrichtian. Averianov and Sues instead proposed a correlation between the Bayanshiree, Iren Dabasu and Bissekty formations. In 2015, Tsuihiji and team found the Iren Dabasu-Nemegt correlation to be inconsistent since the microfossil assemblages used by Van Itterbeeck and colleagues were not restricted to the Maastrichtian period and the similarities between these assemblages were most probably due to a similar deposition and climate settings. ==Paleobiota of the Bayanshiree Formation==

In terms of biodiversity, therizinosaurs and turtles were the most abundant vertebrates across the formation, as evidenced on numerous remains. Nevertheless, hadrosauroids were fairly abundant too, particularly at the Baynshire locality with numerous remains unearthed from this area and a new unnamed hadrosauroid. In addition, most specimens of Gobihadros come from this locality. and the ankylosaurs Talarurus and Tsagantegia. Besides vertebrate fossils, abundant fossil fruits have been collected from the Bor Guvé and Khara Khutul localities and they are especially abundant at Bor Guvé. Although they resemble Abelmoschus esculentus their taxonomic position remains unclear and further examination is required. Crocodylomorphs Fish Flora Mammals Pterosaurs Turtles Dinosaurs Ornithischians Ankylosaurs Ceratopsians Hadrosaurs Pachycephalosaurs Sauropods Theropods Dromaeosaurids Ornithomimosaurs Oviraptorosaurs Therizinosaurs Troodontids Tyrannosauroids Other Theropods == See also ==