Pliocene-pleistocene climatic change recorded in fluviolacustrine sediments in central China

A 250-m-thick section located in the Guanzhong basin, central China, consisting of a loess-paleosol sequence in the upper part and fluviolacustrine sequence in the lower, was selected for this study which involves documenting the climate transition around the global glacial initiation about 2.5 Ma, and focuses on the climatic information recorded in the fluviolacustrine sediments. Paleomagnetic study indicates that the entire Shijiawan section developed during the past 3.08 Ma and the fluviolacustrine sequence spans the time-interval of 3.08-1.9 Ma. Sedimentary analysis shows that alluvial facies dominates the so-called fluviolacustrine sequence with strong cyclicity. Pollen study combined with stable carbon-isotope analysis of organic matter displays profound changes of the paleovegetation in response to climate forcing. During the period of 3.0–2.7 Ma, persistent steppe vegetation and elephant fossil fauna suggest long-lasting dry and warm climate conditions with little change. From 2.7 to 2.5 Ma, sparse steppe flora manifests a striking climatic deterioration. The first thick loess-like layer in the fluviolacustrine sequence consistent with the commencement of the loess deposition in the Loess Plateau marks a rapid and great intensification of the Siberian cold-high pressure regime at 2.6 Ma. Afterwards, the regional vegetation fluctuated between dry steppe and forest-grasslands, in agreement with loess-paleosol alternations, corresponding to the climatic oscillations between cold-dry and warm-wet. Such secular climate variation patterns demonstrate the predominant influence of global glacial and interglacial forcing on the regional climate system of the East Asian monsoon. The late Pliocene climate, warm and dry, is distinct from the harmony of temperature with precipitation (i.e. cold with dry, and warm with wet) which is fully exhibited throughout the past 2.6 Ma. Thus the time of the first global glaciation must have involved a rapid reorganization of the regional climate regime and the onset of the modern East Asian monsoon.