Djadochta Formation

. Djadochta localities at area B. The Djadochta formation was first documented and explored—though only a single locality—during paleontological expeditions of the American Museum of Natural History in 1922–1925, which were part of the Central Asiatic expeditions. The expeditions were led by Roy Chapman Andrews, in company of Walter Willis Granger as chief paleontologist and field team. The team did extensive exploration at the Bayn Dzak (formerly Shabarakh Usu) region, which they nicknamed flaming cliffs, given that at sunset the sediments of this locality had a characteristic reddish color. Notable finds included the first known fossils of Oviraptor, Protoceratops, Saurornithoides, and Velociraptor, the first confirmed dinosaur eggs (a partial nest of Oviraptor), as well as fossil mammals. Some of these were briefly described by Henry Fairfield Osborn during the ongoing years of the expeditions. In 1927 the formation was formally described and established by Berkey and Morris, with Bayn Dzak as the type locality. In 1963 the Mongolian paleontologist Demberelyin Dashzeveg reported the discovery of a new fossiliferous locality of the Djadochta Formation: Tugriken Shireh. During the 1960s to 1970s, Polish-Mongolian and Russian-Mongolian paleontological expeditions collected new, partial to complete specimens of Protoceratops and Velociraptor at this locality, making these dinosaur species a common occurrence in Tugriken Shireh. Some of the most notable excavations made at Tugriken Shireh include the Fighting Dinosaurs (Protoceratops and Velociraptor locked in combat), and abundant articulated, in situ (in the original pose), and sometimes complete skeletons of Protoceratops. During the 1980s a joint Soviet-Mongolian paleontological expedition discovered several Mesozoic fossil-rich localities in the Gobi Desert of Mongolia. Among these sites, Udyn Sayr was discovered and examined by the expedition, regarding its age as Late Cretaceous. This new locality was predominantly rich in avimimid fossils, with a lesser abundance of mammal and other dinosaur fossils. ==Description==

The modern-day Djadochta Formation is set in an arid habitat of sand dunes with little freshwater apart from oases and arroyos, in the Gobi Desert. The dominant lithology of the Djadochta Formation is represented by non-marine, cemented reddish-orange and pale orange to light gray, medium to fine-grained sands and sandstones, which include minor deposits of calcareous concretions and orange-brown silty clay. Less abundant sedimentation comprises conglomerates, siltstones, fluvial (water-deposited) sandstones, and mudstones. The entire thickness of the formation in the Ulan Nur Basin is at least . Several aeolian processes (wind works) indicate the presence of large straight-crested dune-like structures, and smaller barchan (crescent-shaped) and parabolic (poorly U-shaped) dunes across the formation. • Ukhaa Tolgod (also spelled Oka Tolga): The strata exposed at Ukhaa Tolgod is dominated by reddish sandstones, with some sandstones containing small amounts of conglomeratic lenses and/or cobbles and pebbles. Conglomerate itself is in this site, and to a lesser level are mudstones and siltstones, which are thin and laterally restricted. Cross-stratified and fine-structured sandstones are particularly abundant at Ukhaa Tolgod. • Zamyn Khondt (also spelled Dzamyn Khondt, Zamin Khond, or Dzamin Khond): This locality is characterized by reddish, well-sorted, and fine-grained sandstones with calcareous concretions. Some aeolian beds are present and are finely stratified to massive, having a visible thickness of about . ==Stratigraphy and age==

The Djadochta formation occurs in the Late Cretaceous period of the Campanian and Early Maastrichtian stages. Magnetostratigraphic datings from 2006 initially suggested a Campanian age for the formation. If the Djadochta Formation is the same age as the Nemegt Formation, it would be Maastrichtian in age. Because of this uncertainty, the age of the Djadochta is most parsimoniously Campanian to Maastrichtian. The upper boundary of the Djadokhta strata has been identified at the erosional surface overlain by gravels of the Palestine Khashaat (Gashoto) Formation. Further strata from the Bayn Dzak Member includes that of the Ukhaa Tolgod locality, and its overall age is regarded also within the Campanian. Based on the superposition of the members, the Tugrugyin Member overlies the Bayn Dzak Member making it somewhat younger, which indicates that the Bayn Dzak paleofauna lived somewhat earlier than that from Tugriken Shireh. However, it is not yet understood the precise temporal difference: Based on their fossil record and strata, Udyn Sayr and Zamyn Khondt have been correlated with other Djadokhta localities, though fossils of Udyn Sayr may indicate that this locality is younger than Bayn Dzak and Tugriken Shireh. Examinations on the strata of the Alag Teg (also spelled Alag Teeg or Alag Teer) locality, once considered part of this formation, indicates that it belongs to a different geological formation: the Alagteeg Formation, which is slightly older than the overlying Djadochta Formation. Based on sediments and stratigraphic relationships, the lower part of the Bayn Dzak locality is correlated with the Alag Teg locality, making both sections part of the Alagteeg Formation. The upper or main part of the former locality is considered part of the Djadochta Formation itself, as it shares similar lithology and stratigraphic relationships with Tugriken Shireh. ==Depositional environment==

and Western Asia. Low growing bushes may have also existed. It has been suggested that the repeated occurrence of these feeding traces at limb joints may reflect that the responsible scavengers focused on collagen at the joint cartilage of dried dinosaur carcasses as a source of nitrogen, which was very low in the arid Djadochta Formation environments. Examinations at the fossil preservation and sediments of Ukhaa Tolgod indicates that preserved animals were buried alive by catastrophic dune collapses. It is thought to have occurred when sand dunes became oversaturated with water resulting in their sudden downfall; heavy rainfall events likely acted as the triggering mechanism for this collapse. Khaan (a pair in close proximity likely killed by a single collapse event); and Saichangurvel (individual buried alive by a muddy dune). ==Paleobiota==

Among fossils, Protoceratops is extremely common in Djadochta localities. Bayn Dzak is reported as one of the localities with the highest concentration of Protoceratops fossils and has been noted as the "Protoceratops fauna". Although fossil plants are extremely rare in the Djadochta Formation, the great abundancy of herbivorous Protoceratops at the arid-deposited Tugriken Shireh locality indicates that it had a moderate coverage of bushes or other low-growing plants. It is suggested that most of the fragmented hadrosaur, tyrannosaur and sauropod remains across the formation likely belong to non-endemic, passing by species. ==Gallery==

File:Flaming cliffs 1.jpg File:Flaming cliffs in Gobi.jpg File:Flaming cliffs 4.jpg File:Flaming cliffs 8.jpg File:Flaming cliffs 7.jpg ==See also==