Ostracod fauna from the Lower Cretaceous Cangxi Formation of the Sichuan Basin, southwestern China: taxonomy, biostratigraphy and palaeobiogeography

The Cangxi Formation of the Sichuan Basin, southwestern China provides important insights into how palaeoenvironmental conditions influenced the evolution of biota during the Early Cretaceous greenhouse period. However, the application of ostracods from the Sichuan Basin remains highly limited to date. Here, we present a detailed taxonomic analysis of 20 non‐marine ostracod species belonging to seven genera ( Jingguella , Deyangia , Pinnocypridea , Cypridea , Damonella , Cypridoidea gen. indet. and Alicenula ?, including Deyangia rhodopetra sp. nov.) from the Cangxi Formation, along with age constraints and palaeogeographic interpretations. The Cangxi Formation is distinguished from the underlying strata by the presence of Jingguella , Deyangia and Pinnocypridea , and notably represents one of the earliest occurrences of Cypridea in East Asia. This indicates a transitional phase from the non‐ Cypridea fauna to the Cypridea ‐dominated fauna. A comparable faunal transition occurred in northeastern China, although the southwestern region is dominated by jingguellids ( Jingguella and Deyangia ), whereas Luanpingella prevailed in the northeast. The morphological similarity between jingguellids and Luanpingella suggests a close phylogenetic affinity among these taxa. Based on these data, the Cangxi Formation is assigned a Valanginian–Hauterivian age (minimum range of late Valanginian to early Hauterivian). The ostracod fauna dominated by jingguellids closely resembles those from basins along the eastern margin of the Tethys Ocean in Asia and corresponds to the palynofloral province boundary indicative of arid climatic conditions. Therefore, the Cangxi ostracods are crucial for advancing our understanding of the evolution and distribution of biota influenced by palaeogeographic setting and climatic zonation during the Early Cretaceous.