ENVIRONMENTAL MAGNETIC RECORDS OF NIHEWAN LACUSTRINE SEDIMENTS AT XUJIAYAO AND THEIR PALEOCLIMATIC SIGNIFICANCE
许家窑泥河湾沉积物的环境磁学特征

A comparative analysis was performed between magnetic parameters of Pleistocene sediments of the Nihewan Group at Xujiayao and deep sea oxygen isotopic data. There seem to be some parallel or corresponding relations between the two kinds of data, which help to deepen the understanding of Nihewan sediments. These sediments are largely continuous from the Brunhes-Matuyama boundary to the oxygen isotope-based stage 5 (0.13MaB.P.), with a sedimentation rate of about 2.45 cm/10 3a. Like the synchronous loess-paleosol sequences on Chinese Loess Plateau to record climatic and environmental characteristics of Quaternary of North China, Nihewan sediments are characterized by the fact that hematite with a high coercive force significantly increased during the glacial ages, whereas magnetite and maghemite with a low coercive force were dominant magnetic minerals during the interglacial ages. According to the S-ratio (IRM -0.3T/IRM 4T)-based time scale, sediments at the Xujiayao paleoanthropological site give an age of 0.5 MaB.P., which is different from the U-Th age given by fossils reported previously (0.1 MaB.P.). Magnetic parameters in Nihewan sediments show that compared with the magnetic susceptibility k , S-ratio and saturation isothermal remanent magnetization (SIRM) are more suitable to use an alternative paleoclimatic indicator of river-lake sediments. When calculating in the sedimentation rate of 2.45cm/10 3a, the source of Nihewan sediments should be mainly of river-lake facies, but the loess-like dust should not be dominant.