Ilek Formation
{{Short description|Geologic formation in Western Siberia, Russia}}
{{Infobox rockunit
| name = Ilek Formation
| image = Shestakovsky Yar.jpg
| caption = Shestakovo 1 locality
| type = Geological formation
| age = Lower Cretaceous,
Barremian–Aptian
| period = Early Cretaceous
| prilithology = Clay, siltstone
| otherlithology = Marl, sandstone
| namedfor =
| namedby = L. A. Ragozin
| year_ts = 1935
| region = Western Siberia
| country = Russia
| coordinates = {{coord|55.9|N|88.0|E|display=inline,title}}
| paleocoordinates = {{coord|54.2|N|84.6|E|display=inline}}
| unitof = Kiya River Basin
| subunits =
| underlies = Kiya Formation
| overlies = Tyazhin Formation
| thickness = Up to {{Convert|746|m|ft|-1}}
| extent = Kemerovo Oblast
| area =
| map = {{Location map+ | Russia#Russia Kemerovo Oblast
| relief = 1
| width = 250
| float = center
| places =
{{Location map~ | Russia#Russia Kemerovo Oblast
| lat_deg = 55.9
| lon_deg = 88.0
| mark = Green pog.svg
| marksize = 10
}}
}}
| map_caption =
}}
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.
The formation was described by L. A. Ragozin in 1935. It consists of sands with sandstone concretions, layers of silts, clays and marls. Age of the formation, according to a crude 1962 estimate, is Valanginian(?) - Hauterivian - Barremian. Its thickness varies greatly, reaching 746 m in Teguldet borehole. A more recent 2024 estimate based on invertebrate and vertebrate fossils placed the age of the formation at Barremian–Aptian.
Age
The Ilek Formation conformably overlies the Upper Jurassic Tyazhin Formation. 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.
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. 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.
Fauna
= Amphibians =
class="wikitable" align="center"
|+Amphibians reported from the Ilek Formation |
Genus
! Species ! Locality ! Material ! Notes ! Images |
---|
Kiyatriton
|
|Atlas, trunk vertebrae, fragmentary dentaries, femora, humerus, and nearly complete ilium | |
Kuzbassia
|
|Two atlantal centra and a trunk vertebral centrum |A karaurid | |
= Mammaliamorphs =
= Choristoderes =
class="wikitable" align="center"
|+ Choristoderes reported from the Ilek Formation |
Genus
! Species ! Locality ! Material ! Notes ! Images |
---|
style="white-space: nowrap;" | cf. Khurendukhosaurus
|K. cf. sp |
| Dorsal vertebra, sacral vertebra | A non-neochoristodere choristodere | |
colspan="2" style="white-space: nowrap;" | "Shestakovo choristodere"
|
| Fragmentary dentaries, several vertebrae, rib fragments | A possible neochoristodere | |
Choristodera
|Indeterminate |
| Cervical centrum |May represent a taxon distinct from both Khurendukhosaurus and the "Shestakovo choristodere" |
= Lizards =
class="wikitable" align="center"
|+Lizards reported from the Ilek Formation |
Genus
! Species ! Locality ! Material ! Notes ! Images |
---|
Paramacellodidae
|
| | | |
Platynota
|
| | | |
Xenosauridae
|
| | |
= Turtles =
class="wikitable" align="center"
|+Turtles reported from the Ilek Formation |
Genus
! Species ! Locality ! Material ! Notes ! Images |
---|
Kirgizemys
| | | |A macrobaenid | |
= Crocodylomorphs =
class="wikitable" align="center"
|+Crocodylomorphs reported from the Ilek Formation |
Genus
! Species ! Locality ! Material ! Notes ! Images |
---|
Kyasuchus
|
|A partial skull |A shartegosuchid crocodyliform | |
Tagarosuchus
|
|Nearly complete skull | |
= Pterosaurs =
class="wikitable" align="center"
|+ Pterosaurs reported from the Ilek Formation |
Genus
! Species ! Locality ! Material ! Notes ! Image |
---|
?Ctenochasmatidae
|
| | | |
Lonchognathosaurus
|
| Wing metacarpal fragment | A dsungaripterid | |
Ornithocheiridae
|
| | | |
Pterodactyloidea
|
| | | |
= Dinosaurs =
== Sauropodomorphs ==
class="wikitable" align="center"
|+Sauropodomorphs reported from the Ilek Formation |
Genus
! Species ! Locality ! Material ! Notes ! Images |
---|
style="white-space: nowrap;" |Lithostrotia
| |Caudal vertebrae |Potentially three distinct taxa of titanosaur | |
Sibirotitan
| |Vertebrae, sacrum, and pedal elements |A somphospondylan sauropod |
== Ornithischians ==
class="wikitable" align="center"
|+Ornithischians reported from the Ilek Formation |
Genus
! Species ! Locality ! Material ! Notes ! Images |
---|
Ornithischia
|
|Isolated teeth |Originally identified as two distinct "hypsilophodontid" taxa | |
Psittacosaurus
|P. sibiricusAverianov, 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. |
|Several skeletons |A ceratopsian |
Stegosauria
|
| | |
== Theropods ==
See also
References
{{Reflist|refs=
|title=Геологический словарь
|editor = Криштофович А. Н.
|editor-link = Afrikan Nikolaevich Krishtofovich
|date=1955
|volume = 1 (А-Л)
|pages = 271
|chapter = Илекская свита
|publisher = Рипол Классик
|isbn = 9785458366533
|chapter-url=https://books.google.com/books?id=Ad_9AgAAQBAJ&q=свита&pg=PA271
}}
|title=Биостратиграфия мезозойских и третичных отложений Западной Сибири
|editor = Лебедев И. В.
|date=1962
|pages = 168–169
|url=https://books.google.com/books?id=RsybbAazcSAC&q=Илекская&pg=PA168
}}
}}
Category:Geologic formations of Russia
Category:Lower Cretaceous Series of Asia