Ilek Formation
Geologic formation in Western Siberia, Russia
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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]
| Ilek Formation | |
|---|---|
| Stratigraphic range: Lower Cretaceous, Barremian–Aptian | |
 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 | 55.9°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] A more recent 2024 estimate based on invertebrate and vertebrate fossils placed the age of the formation at Barremian–Aptian.[4]
Age
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
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
| Kiyatriton | K. leshchinskiyi[7] |
|
Atlas, trunk vertebrae, fragmentary dentaries, femora, humerus, and nearly complete ilium | A crown-group salamander | |
| Kuzbassia | K. sola[8] |
|
Two atlantal centra and a trunk vertebral centrum | A karaurid |
Mammaliamorphs
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
| Acinacodus | A. tagaricus[9] | Right dentary fragment | An amphidontid mammal | ||
| Baidabatyr | B. clivosus[10] |
|
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] |
|
M1 tooth;[15] mandibular fragments[16] | A docodontan mammaliaform | |
| Xenocretosuchus | X. sibiricus[17] | Dental elements | A tritylodontid mammaliamorph | ||
| Yermakia | Y. domitor[13] |
|
A mandible | A tinodontid mammal |
Choristoderes
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
| cf. Khurendukhosaurus[18] | K. cf. sp |
|
Dorsal vertebra, sacral vertebra | A non-neochoristodere choristodere | |
| "Shestakovo choristodere"[18] |
|
Fragmentary dentaries, several vertebrae, rib fragments | A possible neochoristodere | ||
| Choristodera[18] | Indeterminate |
|
Cervical centrum | May represent a taxon distinct from both Khurendukhosaurus and the "Shestakovo choristodere" | |
Lizards
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
| Paramacellodidae | Indeterminate[4] |
|
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| Platynota | Indeterminate[4] |
|
|||
| Xenosauridae | Indeterminate[4] |
|
A knob-scaled lizard |
Turtles
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
| Kirgizemys | A macrobaenid |
Crocodylomorphs
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
| Kyasuchus | K. saevi[19] |
|
A partial skull | A shartegosuchid crocodyliform | |
| Tagarosuchus | T. kulemzini[20] |
|
Nearly complete skull | A crocodyliform |
Pterosaurs
| Genus | Species | Locality | Material | Notes | Image |
|---|---|---|---|---|---|
| ?Ctenochasmatidae | Indeterminate[13] |
|
|||
| Lonchognathosaurus | L. cf. sp.[21] |
|
Wing metacarpal fragment | A dsungaripterid | |
| Ornithocheiridae | Indeterminate[22] |
|
|||
| Pterodactyloidea | Indeterminate[13] |
|
Dinosaurs
Sauropodomorphs
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
| Lithostrotia | Indeterminate[23] | Caudal vertebrae | Potentially three distinct taxa of titanosaur | ||
| Sibirotitan | S. astrosacralis[5] |
|
Vertebrae, sacrum, and pedal elements | A somphospondylan sauropod |  |
Ornithischians
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
| Ornithischia | Indeterminate[4] |
|
Isolated teeth | Originally identified as two distinct "hypsilophodontid" taxa[25] | |
| Psittacosaurus | P. sibiricus[26] |
|
Several skeletons | A ceratopsian |  |
| Stegosauria | Indeterminate[13] |
|
Isolated teeth[25] |
Theropods
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
| Evgenavis | E. nobilis[27] | A set of limb elements | A confuciusornithiform |  | |
| Kiyacursor | K. longipes[28] |
|
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 | .png) |
| Paraves | Indeterminate[29] | Teeth | May belong to either Microraptorinae or Troodontidae | ||
| Mystiornis | M. cyrili[30] |
|
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 |