Diatom-inferred salinity changes from the Yushe paleolake indicate an aridification during the Pliocene–Pleistocene transition in north China

Abstract

The global climate changed significantly during the Pliocene–Pleistocene transition, and a worldwide aridification occurred.In order to investigate the influence of the aridification during the Pliocene–Pleistocene transition in the East Asian interior, diatom assemblages from the Upper Zhangcun Formation, north China, deposited during 2.7–2.5Ma BP were analyzed, and the lake salinity was reconstructed using diatom–environment transfer functions.A total of 74 diatom taxa were found in the sediments, belonging to 21 families and 32 genera. Four zones were established from the bottom to the top, based on the changes in the diatom assemblages over the 15.7m sediment sequence. In Zone 1, Cyclotella iris dominated in assemblage while Caloneis westii and Staurosira construens were less presented among representative species. In Zone 2, C. iris dominated, which indicates carbonate-rich water. But in Zone 3, benthic pennate taxa such as C. westii and Anomoeoneis sphaerophora became more abundant, indicating a significant increase in water salinity, from carbonate type to sulfate type, caused by climatic change. In Zone 4, C. iris became dominant again, with abundant Gomphonema intricatum and rare Pinnularia rathsbergiana and Martyana martyi species. The salinity inferred by conductivity reconstruction increased from 1.9ppt in Zone 2 to 4.1ppt in Zone 3. The significant changes of anion ratio (Alk/(Cl−+SO42−)) indicate an abrupt change from carbonate-rich to a sulfatic type water.The increase of salinity reflects changes in the precipitation–evaporation balance. The change from carbonate to sulfatic water inferred from the diatom assemblages could indicate a significant aridification around ca. 2.6Ma BP on the eastern edge of the Loess Plateau. This is the most easterly record of aridification across the Eastern Asian interior and may be related with the global cooling and the development of the Northern Hemisphere glaciation.