Occurrence of Middle Miocene Fossil Cyprinid Fish in the Northern Qaidam Basin and its Paleoenvironmental Implications

With a thick sequence of early Eocene to Pleistocene terrestrial records, the Qaidam Basin on the northern Tibetan Plateau provides an important sedimentary archive for understanding the paleoenvironmental evolution of the northeast Tibetan Plateau. In this study, specimens of fossil fish remains are collected from the late Middle Miocene (Serravallian, ~12Ma) of the middle member of the Shang Youshashan Formation, Dahonggou (DHG) section, in the northern Qaidam Basin. Based on a systematic study of these materials, the remains have assigned to Cyprinidae, with typical pharyngeal teeth and dorsal fin spines with serrations on the posterior edge. Our discovery improves understanding of the cyprinid fish distribution characteristics in the Qaidam Basin during the Cenozoic. Co-occurrences of terrestrial brackish ostracod species Cyprideis and long chain alkenonesin the layer indicate that the studied cyprinid fish lived in a generally large brackish to saline water body during the late middle Miocene (Serravallian), when the climate of Qaidam Basin was still not sufficiently dry to form an extreme saline water lake.