我国东北地区黄土堆积的磁性地层年代与古气候变化
摘要
Loess is widely distributed in northeastern China, and is an important geological record of past environmental change. For many years, the lack of a reliable chronology for this set of eolian dust-derived sediments has impeded our understanding of the paleoclimatic evolution and the land surface processes in this region. In this study, an extensive field survey of loess deposits was carried out, and two typical profiles at Niuyangzigou (NYZG) and Pinancun (PAC) were selected for detailed magnetostratigraphy and optically stimulated luminescence dating (OSL). Results showed that the Brunhes/Matuyama magnetic reversal boundary may be pinpointed at a depth of 27 m for the NYZG profiles. The PAC profile does not contain this polarity shift. Thus, the age of the base of these loess deposits should be older than 1.0 Ma, by extrapolating the deposition rate, which was calculated by the magnetostratigraphic control point and the OSL age constraints. Loess is a dust accumulation that forms under semi-arid climate conditions and therefore indicates that a semiarid climate existed in northeastern China at least since the Early Pleistocene. This environmental change corresponds to the global Middle Pleistocene Climate transition, and it may provide evidence that global cooling drove aridity development in central Asia and rapid dust accumulation in northeastern China.