The discovery of ostracods assemblages from Early Cretaceous Chijinpu Formation in Tiancang area, Jiuquan, Gansu Province, and its geological significance

Diverse and abundant ostracods fossils were found from the Tiancang area of Jiuquan, Gansu Province.This research was based on 18 species of ostracods that belong to 7 genera.Based on the age of the fossils and the rock assemblage, we revise the strata to Chijinpu Formation of Early Cretaceous instead of Shuletu Formation of Pliocene in previous research.two assemblages were observed:Cypridea concina-Candona prona-Cypridea zhaobishanensis assemblage in the lower part and Cypridea concina-Cypridea justa-Darwinulla leguminella assemblage in the upper part.The correlation of the ostracods assemblages from the study section with the ostracods fauna in the same strata in other parts of the world indicates that the lower assemblage is of Hauterivian epoch, and the upper assemblage is of Barremian epoch.Based on an analysis of the evolution of fossil morphology and species distribution, the authors hold that the basin was deeper and wider in the Barremian epoch than in the Hauterivian epoch, while the climate showed a tendency of warming and wetting, which had a good response to the global climatic fluctuation events during Early Cretaceous.