PLIOCENE-PLEISTOCENE CLIMATIC-CHANGE RECORDED IN FLUVIOLACUSTRINE SEDIMENTS IN CENTRAL CHINA

A 250-m-thick section located in the Guanzhong basin, central China, c onsisting of a loess-paleosol sequence in the upper part and fluviolac ustrine sequence in the lower, was selected for this study which invol ves documenting the climate transition around the global glacial initi ation about 2.5 Ma, and focuses on the climatic information recorded i n the fluviolacustrine sediments. Paleomagnetic study indicates that t he entire Shijiawan section developed during the past 3.08 Ma and the fluviolacustrine sequence spans the time-interval of 3.08-1.9 Ma. Sedi mentary analysis shows that alluvial facies dominates the so-called fl uviolacustrine sequence with strong cyclicity. Pollen study combined w ith 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 f ossil fauna suggest longlasting dry and warm climate conditions with l ittle change. From 2.7 to 2.5 Ma, sparse steppe flora manifests a stri king climatic deterioration. The first thick loess-like layer in the f luviolacustrine sequence consistent with the commencement of the loess deposition in the Loess Plateau marks a rapid and great intensificati on of the Siberian cold-high pressure regime at 2.6 Ma. Afterwards, th e regional vegetation fluctuated between dry steppe and forest-grassla nds, in agreement with loess-paleosol alternations, corresponding to t he climatic oscillations between cold-dry and warm-wet. Such secular c limate variation patterns demonstrate the predominant influence of glo bal glacial and interglacial forcing on the regional climate system of the East Asian monsoon. The late Pliocene climate, warm and dry, is d istinct from the harmony of temperature with precipitation (i.e. cold with dry, and warm with wet) which is Fully exhibited throughout the p ast 2.6 Ma. Thus the time of the first global glaciation must have inv olved a rapid reorganization of the regional climate regime and the on set of the modern East Asian monsoon. (C) 1997 Elsevier Science B.V.