First record of Pliocene ostracods from the Linxia Formation in Gansu Province, northwestern China (Loess Plateau region) and their palaeoenvironmental implications

Understanding the palaeoenvironment of the Loess Plateau plays a key role in the researches about influences caused by the Tibetan Plateau uplift and the formation of the East Asia Monsoon (EAM). The Longxi area of the Gansu Province, northwestern China, is an ideal area to study such influences because of its unique geographical location within the transition zone among the EAM region, inland arid areas and the northeastern Tibetan Plateau. Here, we present ostracods from a borehole in the Longxi area, as ostracods are one of the few micropalaeontological proxies available in freshwater sediments. The studied ostracods were assigned to 13 species of 10 genera and 9 indeterminate taxa and reported for the first time from the Linxia Formation in the studied area. The ostracod assemblage is composed entirely of non-marine taxa, including species of Ilyocypris, Cypris, Cyprinotus, Heterocypris, Eucypris, Potamocypris, Zonocypris, Candona, Pseudocandona and Leucocythere. Ostracod biostratigraphy indicates that the Linxia Formation should be Pliocene in age. Palaeoenvironmental analysis of the studied ostracod assemblages suggests that there was a permanent freshwater lake with some temporary ponds in the studied area of the Loess Plateau during the Pliocene, which shows the influences of the East Asian Summer Monsoon during the Pliocene.