Ilek Formation
| 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°54′N 88°00′E / 55.9°N 88.0°E |
| Approximate paleocoordinates | 54°12′N 84°36′E / 54.2°N 84.6°E |
| Region | Western Siberia |
| Country | Russia |
| Extent | Kemerovo Oblast |
| Type section | |
| Named by | L. A. Ragozin |
| Year defined | 1935 |
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.