Ostracods from the Eocene Wulagen Formation in the Western Tarim Basin and Their Paleoenvironment

The Middle–Late Eocene Wulagen Formation is widely distributed in the western Tarim Basin. In the Kunlun Mountains Subregion, the Wulagen Formation consists of lower gray-green mudstone and upper variegated mudstone; in the Tianshan Subregion, the Wulagen Formation comprises lower gray-green mudstone and upper gypsum. The Wulagen Formation is rich in ostracods. Based on a preliminary study of the Altaš section, this research identified 17 genera and 29 species, including Haplocytheridea, Cytheridea, Ruggieria, Paracypris, Schizocythere, Paijenborchella, Pterygocythereis, and others. Representative species include Cytheridea scruposa, Cytheidea producta, Haplocytheridea spicula, Haplocytheridea tonsa, Ruggieria pachyodonta, Schizocythere vulgaris, Cytheretta aligra, Cytheretta scrofulosa, Paijenborchella trisulcata, Schuleridea subgratusa, Loxoconcha laculata, Cytherella mirusa, Paracypris elongatissima, among others. Through the analysis of ostracod paleoecology, species diversity, and distribution patterns, it is inferred that the Wulagen Formation was deposited in a shallow marine environment with frequent sea-level fluctuations. Additionally, microgastropod predatory drill holes were observed on some ostracod shells, with the proportion of drilled (preyed upon) ostracods accounting for approximately 2% of the total.