Calcareous green algae (Dasycladales, Halimedaceae) from the Upper Cretaceous of the western Tarim Basin, NW China: Systematic palaeontology, microfacies, and palaeobiogeographic significance

Few stratigraphical and micropalaeontological data are available from Upper Cretaceous shallow-water marine carbonates of the southwestern Tarim Basin, western China. The present study provides new data about the microfauna and calcareous algae of the Cenomanian-Turonian Kukebai Formation and the Campanian Yigeziya Formation. The investigated bioclastic carbonates yield a rather poorly diversified microfauna (benthic foraminifers) contrasting with a relatively well diversified assemblage of dasycladalean green algae comprising 16 taxa. For several taxa, the available material does only allow for an open taxonomic treatment. A new species is described herein as Morelletpora sinica. These calcareous algae are supplemented by debris of halimedacean algae (Arabicodium? sp.). Occurrences of calcareous algae and larger benthic foraminifers in Cenomanian and Campanian carbonates coincide with two major transgressions reported from the Tarim Basin. The observed faunal and phycological elements indicate a direct connection between the Neotethys and the Tarim epicontinental sea. The lack of several typical Cenomanian (e.g., alveolinoids, orbitolinids) and Campanian larger benthic foraminifers in the studied material is striking.