Chakpaktas Formation
Geological formation in Kazakhstan
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Chakpaktas Formation (also known as the Chakpaktas svita) is a geological formation in eastern Kazakstan, as well as being the lowest fossil-bearing strata of the Zaysan Depression. The formation is aged to the Arshantan Asian Land Animal Age which correlates to between the upper Ypresian and lower Lutetian.[1][2]
| Chakpaktas Formation | |
|---|---|
| Stratigraphic range: Middle Eocene, Arshantan | |
| Type | Formation |
| Unit of | Zaysan Depression |
| Underlies | Obaila Formation |
| Thickness | 29 metres (95 ft) |
| Lithology | |
| Primary | mudstone, sandstone |
| Location | |
| Country |  Kazakhstan |
Geology
The Chakpaktas formation is made up of 29 meters of deposits with the sediment transitioning from mudstone to sandstone around midway through.[3] It contains interbedding of quartz and pebbles at the lower parts of the deposit.[4] The mammal localities of the formation can only be found in the southeastern part of the basin which falls in between the Kalmakpay Mountain and Kendyrlyk River.[5]
Paleobiota
Artiodactyla
| Genus | Species | Notes | Image |
|---|---|---|---|
| Aksyiria[6] | A. oligostus | A poorly known dichobunid known from a single molar.[7] | |
| Paraphenacodus[6] | P. solivagus | A large dichobunid known from a single lower molar that shows a bunodont morphology.[7] |
Crocodilia
| Genus | Species | Notes | Image |
|---|---|---|---|
| Pristichampsus [4] | P. kuznetsov | A more terrestrial crocodilian, the genus is of questionable validity as some species have been moved to other genera.[8] It is not completely known where the material attributed to the species is found, though it is most likely to have come from the Chakpaktas Formation.[4] |
Dinocerata
| Genus | Species | Notes | Image |
|---|---|---|---|
| Gobiatherium[3] | G. mirificum | A long-skulled uintathere with an inflated nasal region and flared zygomatic arches similar in shape to what's seen in entelodonts.[3] |  |
Perissodactyla
| Genus | Species | Notes | Image |
|---|---|---|---|
| Eoletes[9] | E. tshakpaktasensis | A hyrachyid known from a fairly complete skull, larger than other species within the genus like E. tianshanicus. It was originally described as the genus Subhyrachyus.[9] | |
| Isectolophus[1] | I. latidens | An isectolophid perissodactyl that helped to confirm the correlation between the Arshantan and Bridgerian land animal ages. The animal lacked the postcanine diastema seen in most ungulates.[1] | |
| Rhodopagus[9] | "R". radinskyi | A hyracodontid that has been noted to be within its own genus rather than being assigned to the genus Rhodopagus.[9] |
Rodentia
| Genus | Species | Notes | Image |
|---|---|---|---|
| Juniperimus[10] | J. flerovi |
Testudine
| Genus | Species | Notes | Image |
|---|---|---|---|
| Altaytrionyx[4] | A. devjatkini | A trionychid turtle.[11] | |
| Geiselemys[4] | G. sp. | A geoemydid turtle that was originally described under the genus grayemys.[12] | |
| Paraplastomenus[4] | P. cf. mlynarskii | A medium-sized trionychid with a large amount of medial contact of the hyopastra and hypoplastra.[13] |