Late Cretaceous Ostracod Biostratigraphy Of Akecheyi Section, Western Tarim Basin, China

Akecheyi region is one of the earliest transgressive sedimentary areas in the western Tarim Basin.Previous studies have done a lot of research on this section,but there are different views on the stratigraphic age.Numerous marine ostracod fossils were found from Kukebai Formation of Akecheyi section in western Tarim Basin,which include 11 genus and 17 species.The discovery of these fossils has great significance for the redefinition of the stratigraphic age and regional stratigraphic division and correlation of the area.According to the distribution of ostracod fossils in the formation,three assemblages are recognized in ascending order: Ovocytheridea bashibulakeensis–Ovocytheridea akedaoensis–Cytherella cf.anteromarginata zone?Ovocytheridea–Procytherura sp.1 zone and Ovocytheridea akedaoensis–Pontocyprella proceraformis–Haplocytheridea sp.2 zone.By comparing these data with those of other regions,it is considered that the geological age of the three assemblage zones are late Cenomanian–early Turonian,middle Turonian and late Turonian–late Santonian.On this basis,combined with other kinds of biostratigraphy(foraminifera,calcareous nannofossils,bivalves)and previous research results on the late Cretaceous geological age,it is determined that the geologic time of Kukebai Formation of Akecheyi section should be early–middle Cenomanian–late Santonian(The geological time of lower section of Kukebai Formation should be the early–middle Cenomanian;the geological time of middle section of Kukebai Formation should be late Cenomanian–early Turonian;the geological time of upper section of Kukebai Formation should be the middle Turonian–late Santonian).The geological time of Wuyitage Formation and Yigeziya Formation should be Campanian–Maastrichtian.