Ilek Formation
Stratigraphic range: Lower Cretaceous,
Barremian–Aptian

File:Shestakovsky Yar.jpg

Shestakovo 1 locality

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°54′N 88°00′E﻿ / ﻿55.9°N 88.0°E﻿ / 55.9; 88.0
Paleocoordinates|  [ ⚑ ] 54°12′N 84°36′E﻿ / ﻿54.2°N 84.6°E﻿ / 54.2; 84.6
Region| Western Siberia
Country| Russia
Extent| Kemerovo Oblast
Type section
Named by| L. A. Ragozin
Year defined| 1935

Ilek Formation (Russia)

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Ilek Formation (Kemerovo Oblast)

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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]

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] A more recent 2024 estimate based on invertebrate and vertebrate fossils placed the age of the formation at Barremian–Aptian.[4]

## Contents

* 1 Age
* 2 Fauna
* 2.1 Amphibians
* 2.2 Mammaliamorphs
* 2.3 Choristoderes
* 2.4 Lizards
* 2.5 Turtles
* 2.6 Crocodylomorphs
* 2.7 Pterosaurs
* 2.8 Dinosaurs
* 2.8.1 Sauropodomorphs
* 2.8.2 Ornithischians
* 2.8.3 Theropods
* 3 See also
* 4 References

## Age

File:Shestakovo 3.jpgShestakovo 3 locality

The Ilek Formation conformably overlies the Upper Jurassic Tyazhin Formation.[1] Gastropods and bivalves of Valanginian age have been recovered from the lower part of the formation, and gastropods and bivalves of Hauterivian to Barremian age have been found in the upper part, as well as Barremian ostracods. The age of the Shestakovo 1 locality is poorly constrained.[5] Palynological samples from the Shestakovo 3 locality are characteristic of the Aptian. No angiosperm pollen has been found at this locality, indicating that it is older than the Albian.[6] The upper layers of the formation do contain angiosperm pollen, indicating that part of the formation may extend into the Albian. The overlying Kiya Formation is upper Albian based on plant biostratigraphy.[1]

## Fauna

### Amphibians

Amphibians reported from the Ilek Formation  Genus  | Species  | Locality  | Material  | Notes  | Images

|
|
|
|
|

Kiyatriton | K. leshchinskiyi[7] |

* Shestakovo 1

| Atlas, trunk vertebrae, fragmentary dentaries, femora, humerus, and nearly complete ilium  | A crown-group salamander |
Kuzbassia | K. sola[8] |

* Shestakovo 1

| Two atlantal centra and a trunk vertebral centrum  | A karaurid |

### Mammaliamorphs

Mammaliamorphs reported from the Ilek Formation  Genus  | Species  | Locality  | Material  | Notes  | Images

|
|
|
|
|

Acinacodus | A. tagaricus[9] |  | Right dentary fragment  | An amphidontid mammal  |
Baidabatyr | B. clivosus[10] |

* Bol'shoi Kemchug 3

| Upper premolar  | A multituberculate  |
Gobiconodon | G. borissiaki[11] |  | 21 upper and lower jaws.  | A gobiconodont  |
G. hoburensis[12] |  | A fragmentary lower jaw.
Kemchugia | K. magna[13] |  | A tooth  | An amphilestid mammal  |
Kiyatherium | K. cardiodens[14] |  | A maxilla  | A zhangheotheriid mammal  |
Sibirotherium | S. rossicum[15] |

* Bol'shoi Kemchug 4

| M1 tooth;[15] mandibular fragments[16] | A docodontan mammaliaform  |
Xenocretosuchus | X. sibiricus[17] |  | Dental elements  | A tritylodontid mammaliamorph  |
Yermakia | Y. domitor[13] |

* Shestakovo 1

| A mandible  | A tinodontid mammal  |

### Choristoderes

Choristoderes reported from the Ilek Formation  Genus  | Species  | Locality  | Material  | Notes  | Images

|
|
|
|
|

cf. Khurendukhosaurus[18] | K. cf. sp  |

* Bol'shoi Kemchug 3

| Dorsal vertebra, sacral vertebra  | A non-neochoristodere choristodere  |
"Shestakovo choristodere"[18] |

* Shestakovo
* Bol'shoi Kemchug 3
* Bol'shaya Terekhtul' 2

| Fragmentary dentaries, several vertebrae, rib fragments  | A possible neochoristodere  |
Choristodera[18] | Indeterminate  |

* Smolenskii Yar

| Cervical centrum  | May represent a taxon distinct from both Khurendukhosaurus and the "Shestakovo choristodere"

### Lizards

Lizards reported from the Ilek Formation  Genus  | Species  | Locality  | Material  | Notes  | Images

|
|
|
|
|

Paramacellodidae | Indeterminate[4] |

* Kemchug assemblage
* Kiya assemblage

|  |  |
Platynota | Indeterminate[4] |

* Kemchug assemblage

|  |  |
Xenosauridae | Indeterminate[4] |

* Kemchug assemblage
* Kiya assemblage

|  | A knob-scaled lizard  |

### Turtles

Turtles reported from the Ilek Formation  Genus  | Species  | Locality  | Material  | Notes  | Images

|
|
|
|
|

Kirgizemys |  |  |  | A macrobaenid  |

### Crocodylomorphs

Crocodylomorphs reported from the Ilek Formation  Genus  | Species  | Locality  | Material  | Notes  | Images

|
|
|
|
|

Kyasuchus | K. saevi[19] |

* Shestakovo 3

| A partial skull  | A shartegosuchid crocodyliform  |
Tagarosuchus | T. kulemzini[20] |

* Shestakovo 3

| Nearly complete skull  | A crocodyliform  |

### Pterosaurs

Pterosaurs reported from the Ilek Formation  Genus  | Species  | Locality  | Material  | Notes  | Image

|
|
|
|
|

?Ctenochasmatidae | Indeterminate[13] |

* Bol'shoi Kemchug 3

|  |  |
Lonchognathosaurus | L. cf. sp.[21] |

* Novochernorechensk

| Wing metacarpal fragment  | A dsungaripterid  |
Ornithocheiridae | Indeterminate[22] |

* Shestakovo 1

|  |  |
Pterodactyloidea | Indeterminate[13] |

* Bol'shoi Kemchug 3

|  |  |

### Dinosaurs

#### Sauropodomorphs

Sauropodomorphs reported from the Ilek Formation  Genus  | Species  | Locality  | Material  | Notes  | Images

|
|
|
|
|

Lithostrotia | Indeterminate[23] |  | Caudal vertebrae  | Potentially three distinct taxa of titanosaur |
Sibirotitan | S. astrosacralis[5] |

* Shestakovo 1
* Shestakovo 3[24]

| Vertebrae, sacrum, and pedal elements  | A somphospondylan sauropod  |

#### Ornithischians

Ornithischians reported from the Ilek Formation  Genus  | Species  | Locality  | Material  | Notes  | Images

|
|
|
|
|

Ornithischia | Indeterminate[4] |

* Shestakovo 1
* Bol'shoi Kemchug 3

| Isolated teeth  | Originally identified as two distinct "hypsilophodontid" taxa[25] |
Psittacosaurus | P. sibiricus[26] |

* Shestakovo

| Several skeletons  | A ceratopsian |
Stegosauria  | Indeterminate[13] |

* Bol'shoi Kemchug 3

| Isolated teeth[25] |  |

#### Theropods

Theropods reported from the Ilek Formation  Genus  | Species  | Locality  | Material  | Notes  | Images

|
|
|
|
|

Evgenavis | E. nobilis[27] |  | A set of limb elements  | A confuciusornithiform  |
Kiyacursor | K. longipes[28] |

* Shestakovo 1

| Partial skeleton including cervical and caudal vertebrae, cervical and dorsal ribs, a left scapulocoracoid, humeri, and much of both hind limbs[28] | A noasaurid theropod  | File:Kiyacursor PM (white bg).png
Paraves | Indeterminate[29] |  | Teeth  | May belong to either Microraptorinae or Troodontidae |
Mystiornis | M. cyrili[30] |

* Shestakovo 1

| Isolated metatarsus  | An avisaurid enantiornithean  |
Paraves | Indeterminate[29] |  | Teeth  | May belong to either Microraptorinae or Troodontidae |
Tyrannosauroidea | Indeterminate[29] |  | Teeth  |  |
Urbacodon | U. cf. sp.[29] |  | Teeth  | A troodontid with unserrated teeth

## See also

* List of pterosaur-bearing stratigraphic units

## References

1. ↑ 1.0 1.1 1.2 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. Bibcode: 2010SGC....18..153G.
2. ↑ Криштофович А. Н., ed (1955). "Илекская свита". Геологический словарь. 1 (А-Л). Рипол Классик. pp. 271. ISBN 9785458366533. https://books.google.com/books?id=Ad_9AgAAQBAJ&q=свита&pg=PA271.
3. ↑ Лебедев И. В., ed (1962). Биостратиграфия мезозойских и третичных отложений Западной Сибири. pp. 168–169. https://books.google.com/books?id=RsybbAazcSAC&q=Илекская&pg=PA168.
4. ↑ 4.0 4.1 4.2 4.3 4.4 Ivantsov, S. V.; Fayngerts, A. V.; Feofanova, O. A.; Vladimirova, O. N.; Slobodin, D. A. (2024). "Early Cretaceous continental sedimentatary environments, palaeogeography and biota of southeastern Western Siberia". Geological Society, London, Special Publications 545: 627–641. doi:10.1144/SP545-2023-62.
5. ↑ 5.0 5.1 Averianov, Alexander; Ivantsov, Stepan; Skutschas, Pavel; Faingertz, Alexey; Leshchinskiy, Sergey (2018). "A new sauropod dinosaur from the Lower Cretaceous Ilek Formation, Western Siberia, Russia". Geobios 51 (1): 1–14. doi:10.1016/j.geobios.2017.12.004. ISSN 0016-6995. Bibcode: 2018Geobi..51....1A.
6. ↑ Bugdaeva, E V; Markevich, V S; Volynets, E B (2017). "Palaeoenvironmental and palaeoclimatic reconstruction of the Early Cretaceous psittacosaur localities, Asia". Fifth International Symposium of International Geoscience Programme. Jeju Island, Korea. pp. 31–34.
7. ↑ Skutschas, P. P. (2014). "Kiyatriton leshchinskiyi Averianov et Voronkevich, 2001, a crown-group salamander from the Lower Cretaceous of Western Siberia, Russia". Cretaceous Research 51: 88–94. doi:10.1016/j.cretres.2014.05.014. ISSN 0195-6671. Bibcode: 2014CrRes..51...88S. https://www.sciencedirect.com/science/article/pii/S0195667114001062.
8. ↑ Skutschas, P.; Kolchanov, V.; Anpilogova, E.; Parakhin, I.; Averianov, A.; Jones, M. (2023). "The last of them? A new relic karaurid stem salamander from the Lower Cretaceous of Western Siberia, Russia". Biological Communications 68 (4): 219–226. doi:10.21638/spbu03.2023.402.
9. ↑ 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.
10. ↑ 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.
11. ↑ Trofimov, B. A. (1978). "The first triconodonts (Mammalia, Triconodonta) from Mongolia". Doklady Akademii Nauk SSSR. 243 (1): 213–216.
12. ↑ 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.
13. ↑ 13.0 13.1 13.2 13.3 13.4 Averianov, A. O.; Skutschas, P. P.; Lopatin, A. V.; Leshchinskiy, S. V.; Rezvyi, A. S.; Fayngerts, A. V. (2005). "Early Cretaceous mammals from Bol'shoi Kemchug 3 locality in West Siberia, Russia". Russian Journal of Theriology 4 (1): 1–12. doi:10.15298/rusjtheriol.04.1.01. https://www.researchgate.net/publication/235806746.
14. ↑ E. N. Maschenko and A. V. Lopatin. 2002. A new Early Cretaceous mammal from Western Siberia. Doklady Biological Sciences 386:475-477
15. ↑ 15.0 15.1 Lopatin, A. V.; Averianov, A. O.; Ivantsov, S. V.; Kuzmin, I. T.; Skutschas, P. P. (2023-07-19). "An Upper Molar of a Docodontan (Docodonta, Mammaliaformes) from the Lower Cretaceous of Western Siberia" (in en). Doklady Earth Sciences 512 (1): 871–873. doi:10.1134/S1028334X23601128. ISSN 1028-334X. Bibcode: 2023DokES.512..871L. https://link.springer.com/10.1134/S1028334X23601128.
16. ↑ Maschenko, E. N.; Lopatin, A. V.; Voronkevich, A. V. (2002). "A new genus of the tegotheriid docodonts (Docodonta, Tegotheriidae) from the Early Cretaceous of West Siberia". Russian Journal of Theriology 1 (2): 75–81. doi:10.15298/rusjtheriol.01.2.01. http://zmmu.msu.ru/rjt/articles/article.php?volume=1&issue=2&pages=75-81.
17. ↑ "Fossilworks: Stereognathus". https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=254183.
18. ↑ 18.0 18.1 18.2 Skutschas, Pavel P.; Vitenko, Dmitriy D. (2017-05-04). "Early Cretaceous choristoderes (Diapsida, Choristodera) from Siberia, Russia". Cretaceous Research 77: 79–92. doi:10.1016/j.cretres.2017.05.004. ISSN 0195-6671. Bibcode: 2017CrRes..77...79S.
19. ↑ 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.
20. ↑ Fiorelli, L.E.; Calvo, J.O. (2007). "The first "protosuchian" (Archosauria: Crocodyliformes) from the Cretaceous (Santonian) of Gondwana" (PDF).
21. ↑ Averianov, Alexander O.; Ivantsov, Stepan V.; Leshchinskiy, Sergey V.; Skutschas, Pavel P. (2022-09-01). "First pterosaur bone from the Lower Cretaceous of Siberia, Russia" (in en). Cretaceous Research 137. doi:10.1016/j.cretres.2022.105230. ISSN 0195-6671. Bibcode: 2022CrRes.13705230A. https://www.sciencedirect.com/science/article/pii/S0195667122000945.
22. ↑ Skutschas, P. (2006). "Mesozoic amphibians from Siberia, Russia". 9th International Symposium on Mesozoic Terrestrial Ecosystems and Biota, Abstracts and Proceedings Volume: 123–126. https://www.researchgate.net/publication/285315220.
23. ↑ 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. doi:10.1016/j.cretres.2019.104309. Bibcode: 2020CrRes.10704309A.
24. ↑ Averianov, A.; Podlesnov, A.; Slobodin, D.; Skutschas, P.; Feofanova, O.; Vladimirova, O. (2023). "First sauropod dinosaur remains from the Early Cretaceous Shestakovo 3 locality, Western Siberia, Russia". Biological Communications 68 (4): 236–252. doi:10.21638/spbu03.2023.404.
25. ↑ 25.0 25.1 Averianov, A. O.; Leshchinskiy, S. V.; Skutschas, P. P.; Fayngertz, A. V.; Rezvyi, A. S. (2004). "Dinosaurs from the Early Cretaceous Ilek Formation in West Siberia, Russia". Second European Association of Vertebrate Paleontologists Meeting. Abstracts of Papers 6: 6. https://www.researchgate.net/publication/235807189.
26. ↑ 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.
27. ↑ 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.
28. ↑ 28.0 28.1 Averianov, A. O.; Skutschas, P. P.; Atuchin, A. A.; Slobodin, D. A.; Feofanova, O. A.; Vladimirova, O. N. (2024). "The last ceratosaur of Asia: a new noasaurid from the Early Cretaceous Great Siberian Refugium". Proceedings of the Royal Society B: Biological Sciences 291 (2023): 20240537. doi:10.1098/rspb.2024.0537. PMID 38747705.
29. ↑ 29.0 29.1 29.2 29.3 Averianov, A.O.; Ivantsov, S.V.; Skutschas, P.P. (2019-06-25). "Theropod teeth from the Lower Cretaceous Ilek Formation of Western Siberia, Russia" (in ru). Proceedings of the Zoological Institute of the Russian Academy of Sciences 323 (2): 65–84. doi:10.31610/trudyzin/2019.323.2.65. ISSN 0206-0477.
30. ↑ 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.

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