ASSESSMENT OF THE PALAEOCLIMATE DURING 3.0-2.6 MA REGISTERED BY TRANSITION OF RED CLAY TO LOESS-PALEOSOL SEQUENCE IN CENTRAL NORTH CHINA

A continuously accumulated section (the Yanyu section) of Red Clay and loess-paleosol sequence from the southernmost Chinese Loess Plateau was selected for this study of palaeoclimate of the late Pliocene to early Pleistocene period. Termination of the Red Clay accumulation and onset of loess deposition was coincident with the beginning of extensive Northern Hemisphere glaciation at 2.6 Ma. Field observations and compositional analyses suggest an eolian origin for the Red Clay, much like the processes experienced by the loess-paleosol sequence. Pedogenic analysis indicates that the late Pliocene Red Clay first experienced complete decalcification and illuviation (mechanical translocation of clays) in all horizons, including the present carbonate precipitation zones, but other chemical alterations have been rather weak and even weaker than experienced by the overlying loess-derived paleosols. In great contrast to the Pleistocene climate characterized by frequent and large-amplitude fluctuations between cold-dry and warm-wet, a relatively steady warm-dry climate condition is implied for the late Pliocene. Dustfall rate assessment indicates a much lower accumulation rate during the late Pliocene than in the early Pleistocene, in agreement with a notable systematic coarsening from the Red Clay to the overlying loess and paleosols. Together, these features suggest that the dust transport agent, the northwesterly winds, were weaker over the late Pliocene. The transition from Red Clay to loess possibly marked a significant and rapid shift in the climatic system in east Asia.