Ilek Formation

The Ilek Formation is a Lower Cretaceous geologic formation in Western Siberia. Many different fossils have been recovered from the formation. It overlies the Late Jurassic Tyazhin Formation and underlies the Albian Kiya Formation.[1]

Ilek Formation Stratigraphic range: Lower Cretaceous PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Unit of	Kiya River Basin
Underlies	Kiya Formation
Overlies	Tyazhin Formation
Thickness	Up to 746 metres (2,450 ft)
Lithology
Primary	Clay, siltstone
Other	Marl, sandstone
Location
Coordinates	55.9°N 88.0°E
Approximate paleocoordinates	54.2°N 84.6°E
Region	Western Siberia
Country	Russia
Extent	Kemerovo Oblast
Type section
Named by	L. A. Ragozin
Year defined	1935
Ilek Formation (Russia) Ilek Formation (Kemerovo Oblast)

The formation was described by L. A. Ragozin in 1935. It consists of sands with sandstone concretions, layers of silts, clays and marls.[2] Age of the formation, according to a crude 1962 estimate, is Valanginian(?) - Hauterivian - Barremian. Its thickness varies greatly, reaching 746 m in Teguldet borehole.[3]

Fauna

Dinosaurs reported from the Ilek Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Evgenavis[4]	E. nobilis	Siberia		A set of limb elements	A confuciusornithiform
Mystiornis[5]	M. cyrili	Western Siberia	Shestakovo-1 locality	Isolated metatarsus	An avisaurid enantiornithean
Psittacosaurus[6]	P. sibiricus	Western Siberia	Shestakovo	Several skeletons	A ceratopsian
Sibirotitan[7]	S. astrosacralis	Western Siberia		Vertebrae, sacrum, and previously published pedal elements	A somphospondylan
Dromaeosauridae[8]	Indeterminate			Teeth
Lithostrotia indet.[9]	Indeterminate	Western Siberia		Caudal vertebrae	A titanosaur
?Tyrannosauroidea	Indeterminate			Teeth

Turtles reported from the Ilek Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Kirgizemys	Indeterminate				A macrobaenid

Crocodylomorphs reported from the Ilek Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Kyasuchus[10]	K. saevi	Siberia		A partial skull	A shartegosuchid crocodyliform
Tagarosuchus[11]	T. kulemzini	Southern Siberia	Shestakovo	Nearly complete skull	A crocodyliform

Mammaliamorphs reported from the Ilek Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Acinacodus[12]	A. tagaricus	Western Siberia		Right dentary fragment	An amphidontid mammal
Baidabatyr[13]	B. clivosus	Siberia	Bol'shoi Kemchug 3 locality	Upper premolar	A multituberculate
Gobiconodon	G. hoburensis[14]	Siberia		21 upper and lower jaws.	A gobiconodont
	G. borissiaki[15]	Siberia		A fragmentary lower jaw	A gobiconodont
Kemchugia[16]	K. magna			A tooth	An amphilestid mammal
Kiyatherium[17]	K. cardiodens	Western Siberia		A maxilla	A zhangheotheriid mammal
Sibirotherium[18]	S. rossicus	Siberia		Lower jaw fragments	A docodont mammaliaform
Xenocretosuchus[19]	X. sibiricus	Siberia		Dental elements	A tritylodontid mammaliamorph
Yermakia[16]	Y. domitor	Siberia	Shestakovo-1 locality	A mandible	A tinodontid mammal

Amphibians reported from the Ilek Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Kiyatriton	K. leshchinskiyi	Western Siberia		A set of vertebrae	A salamander

Lizards reported from the Ilek Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Ilekia[20]	I. sibirica	Western Siberia	Bol'shoi Kemchug 3 locality		A member of Paramacellodidae
Shestakovia	S. voronkevichi	Western Siberia	Bol'shoi Kemchug 3 locality		A knob-scaled lizard

See also

• List of pterosaur-bearing stratigraphic units

References

1. Golovneva, L. B.; Shchepetov, S. V. (April 2010). "Phytostratigraphy of Albian-Cenomanian sediments in the Kiya River basin (the Chulym-Yenisei area of the west Siberian lowland)". Stratigraphy and Geological Correlation. 18 (2): 153–165. doi:10.1134/s0869593810020048. ISSN 0869-5938.
2. Криштофович А. Н., ed. (1955). "Илекская свита". Геологический словарь. 1 (А-Л). p. 271.
3. Лебедев И. В., ed. (1962). Биостратиграфия мезозойских и третичных отложений Западной Сибири. pp. 168–169.
4. O'Connor, JL; Averianov, AO; Zelenkov, NV (2014). "A confuciusornithiform (Aves, Pygostylia)-like tarsometatarsus from the Early Cretaceous of Siberia and a discussion of the evolution of avian hind". Journal of Vertebrate Paleontology. 34 (3): 647–656. doi:10.1080/02724634.2013.828734.
5. Evgeny N. Kurochkin; Nikita V. Zelenkov; Alexandr O. Averianov; Sergei V. Leshchinskiy (2011). "A new taxon of birds (Aves) from the Early Cretaceous of Western Siberia, Russia". Journal of Systematic Palaeontology. 9 (1): 109–117. doi:10.1080/14772019.2010.522202.
6. Averianov, Alexander O.; Voronkevich, Alexei V.; Leshchinskiy, Sergei V.; Fayngertz, Alexei V. (2006). "A ceratopsian dinosaur Psittacosaurus sibiricus from the Early Cretaceous of West Siberia, Russia and its phylogenetic relationships". Journal of Systematic Palaeontology. 4 (4): 359–395. doi:10.1017/s1477201906001933.
7. Alexander Averianov; Stepan Ivantsov; Pavel Skutschas; Alexey Faingertz; Sergey Leshchinskiy (2018). "A new sauropod dinosaur from the Lower Cretaceous Ilek Formation, Western Siberia, Russia". Geobios. in press. doi:10.1016/j.geobios.2017.12.004.
8. Averianov, A.O.; Ivantsov, S.V.; Skutschas, P.P. (2019-06-25). "Theropod teeth from the Lower Cretaceous Ilek Formation of Western Siberia, Russia". Proceedings of the Zoological Institute of the Russian Academy of Sciences (in Russian). 323 (2): 65–84. doi:10.31610/trudyzin/2019.323.2.65. ISSN 0206-0477.
9. Alexander O. Averianov; Stepan V. Ivantsov; Pavel P. Skutschas (2020). "Caudal vertebrae of titanosaurian sauropod dinosaurs from the Lower Cretaceous Ilek Formation in Western Siberia, Russia". Cretaceous Research. 107: Article 104309. doi:10.1016/j.cretres.2019.104309.
10. Efimov, M. B. and Leshchinskiy, S. V. (2000). First finding of the fossil crocodile skull in Siberia [in Russian]. In: Komarov, A. V., ed., Materialy regional’noj konferencii geologov Sibiri, Dal’nego Vostoka i Severo−Vostoka Rossii. Tom II, 361–363. GalaPress, Tomsk.
11. Fiorelli, L.E.; Calvo, J.O. (2007). "The first "protosuchian" (Archosauria: Crocodyliformes) from the Cretaceous (Santonian) of Gondwana" (PDF).
12. A. V. Lopatin; E. N. Maschenko & A. O. Averianov (2010). "A new genus of triconodont mammals from the Early Cretaceous of Western Siberia". Doklady Biological Sciences. 433 (1): 282–285. doi:10.1134/S0012496610040137.
13. Alexander Averianov; Alexey Lopatin; Pavel Skutschas; Stepan Ivantsov; Elizaveta Boitsova; Ivan Kuzmin (2017). "An enigmatic multituberculate mammal from the Early Cretaceous of Siberia, Russia". Journal of Vertebrate Paleontology. 37 (2): e1293070. doi:10.1080/02724634.2017.1293070.
14. Trofimov, B. A. (1978). "The first triconodonts (Mammalia, Triconodonta) from Mongolia". Doklady Akademii Nauk SSSR. 243 (1): 213–216.
15. Maschenko, E. N.; Lopatin, A. V. (1998). "First record of an Early Cretaceous triconodont mammal in Siberia". Bull. Inst. R. Sci. Nat. Belg. 68: 233–236.
16. A. V. Lopatin, E. N. Maschenko, A. O. Averianov, A. S. Rezvyi, P. P. Skutschas and S. V. Leschinskiy. 2005. Early Cretaceous Mammals from Western Siberia: 1. Tinodontidae. Paleontological Journal 39(5):523-534
17. E. N. Maschenko and A. V. Lopatin. 2002. A new Early Cretaceous mammal from Western Siberia. Doklady Biological Sciences 386:475-477
18. http://zmmu.msu.ru/rjt/articles/article.php?volume=1&issue=2&pages=75-81
19. http://fossilworks.org/cgi-bin/bridge.pl?a=taxonInfo&taxon_no=254183
20. A. O. Averianov, P. P. Skutschas, A. V. Lopatin, S. V. Leschinskiy, A. S. Rezvyi and A. V. Fayngerts. 2005. Early Cretaceous mammals from Bol'shoi Kemchug 3 locality in West Siberia, Russia. Russian Journal of Theriology 4(1):1-12