Non-marine ostracod fauna from the Cretaceous Xiagou Formation (Jiuquan Basin, NW China): Taxonomy, biostratigraphy, palaeogeography and palaeoenvironment

Abstract

The non-marine ostracod fauna of the Xiagou Formation of the Chijinpu Group in the Jiuquan Basin of northwestern China includes Bisulcocypridea astuta, Cypridea koskulensis, C. yumenensis, C. latiovata, C. cf. elegantula, Limnocypridea? diwopuensis, Candona sp., Lycopterocypris debilis, Mongolianella gigantea, Rhinocypris jurassica, Ziziphocypris costata, Alicenula? leguminella, Limnocythere xiagouensis and L. fragilis. Comparison of the Xiagou Formation ostracod fauna with those from Northeast China, Mongolia, Central Asia and Russia indicates that the Xiagou Formation is Aptian in age. The stratigraphic ranges of the Cypridea valdensis–parallela group, R. jurassica and L. fragilis are extended to the Aptian. The known distributions of ostracod taxa—especially the Cypridea valdensis–parallela group, Bisulcocypridea and L. fragilis—in ostracod faunas of Europe, Asia and North America provides evidence that intercontinental and continental ostracod faunal exchanges were active during the Early Cretaceous. Dispersal of these ostracods occurred alongside known dispersal events of non-marine vertebrates between Asia and Europe as well as between Asia and North America, which may imply that large animals (i.e., dinosaurs) played an important role in intercontinental invertebrate faunal interchange. In addition, Aptian palaeolakes/ponds in northwestern China were important in forming isolated environments for the explosive radiation of the superfamilies Cypridoidea and Cytheroidea, and they also provided non-marine habitats for the migration of ostracod species from other continents. The ostracod fauna indicates that the Xiagou Formation represents a fresh to slightly saline shallow to littoral-marginal lacustrine environment with a fluvial influence that may have included shallow temporary waterbodies (e.g., ponds).