The Ustmylian Gorizont ("Ustmylian Horizon") is a

Lower Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is a un ...

biostratigraphic unit in Western

Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...

. The Ustmylian Gorizont is the youngest subunit of the Vetlugian Supergorizont, lying above the Sludkian Gorizont and below the Yarenskian Gorizont. It corresponds to the later part of the early Olenekian stage. Along with the Sludkian Gorizont, the Ustmylian Gorizont is encompassed by the "''

Wetlugasaurus ''Wetlugasaurus'' (meaning "Vetluga River lizard") is an extinct genus of Temnospondyli, temnospondyl amphibian from the Early Triassic (Olenekian) Charkabozh Formation, Charkabozh, Kzylsaiskaya Formation, Kzylsaiskaya, Petropavlovka Formation, ...

'' fauna", named after a

capitosaur Capitosauria is an extinct group of large temnospondyl amphibians with simplified stereospondyl vertebrae. Mainly living as piscivores in lakes and rivers, the Capitosauria and its sister taxon Trematosauria were the only major labyrinthodonts t ...

amphibian index fossil. While the Sludkian is characterized by ''Wetlugasaurus angustifrons'', the Ustmylian is characterized by ''Wetlugasaurus malachovi''. The Ustmylian is exposed in several svitas (equivalent to

geological formations A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

) spread out over a wide area. These include the upper part of the Charkabozhskaya Svita (Charkabozh Formation) in the Pechora Basin, the Bereznikovskaya Svita in the Moscow Syncline, the Pizhmomezen'skaya Svita near the Mezen River, and the Gostevskaya Svita near the

Samara River The Samara ( rus, Сама́ра, p=sɐˈmarə) is a river in Russia and a left-bank tributary of the Volga. It flows into the larger river at the city of Samara. Its largest tributary is the Bolshoy Kinel. It is long, and its drainage basin ...

. Differentiating the Sludkian and Ustmylian can be difficult elsewhere.

References

Geologic formations of Russia Triassic System of Europe Triassic Russia Olenekian Stage Paleontology in Russia {{Europe-geologic-formation-stub