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| 黄土频率磁化率与古气候冷暖变换 | |
| 引用本文： | 刘秀铭,刘东生,F. Heller,许同春.黄土频率磁化率与古气候冷暖变换[J].第四纪研究,1990,10(1):42-50. |
| 作者姓名： | 刘秀铭 刘东生 F. Heller 许同春 |
| 作者单位： | 中国科学院地质研究所，中国科学院地质研究所，瑞士联邦苏黎世高等理工大学，国家地震局地球物理研究所 中国科学院西安黄土与第四纪地质开放研究实验室 |
| 摘 要： | 本文详细研究和对比了几个区域的黄土剖面,证明中国黄土地层发育的一致性;根据第5阶段以来黄土磁化率和深海氧同位素曲线特征的比较,证明中国黄土地层的连续性和全球气候变化的一致性。黄土地层的古气候信息强度与分辨率成反比,是全球信号和区域信号的叠加。黄土高原各地厚度或沉积速率的差别主要是1.7 Ma以来形成的。黄土地层频率磁化率数值随黄土和古土壤层的出现,分别呈波谷和波峰对应,说明在温湿条件下有许多细小(<0.03 μm)的铁磁性矿物形成,它可能是导致古土壤磁化率增高的最主要原因。这些磁颗粒的含量反映古气候温湿程度的强弱和持续时间的长短。黄土频率磁化率对古气候的突变或渐变研究可能具有十分重要的意义。 |
| 关 键 词： | 中国黄土地层 频率磁化率 第四纪古气候 冷暖变换 |
FREQUENCY-DEPENDENT SUSCEPTIBILITY OF LOESS AND QUATERNARY PALEOCLIMATE |
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| Institution: | 1. Institute of Geology, Chinese Academy of Sciences; 2. Institute of Geophysics, ETH-Honggerberg CH-8093 Zurich, Switzerland; 3. Institute of Geophysics, State Seismological Bureau |
| Abstract: | A continuous loess stratigraphy provides a basis for study of Quaternary climate. There is a correlation between the loess profiles in Xifeng and Baicaoyuan, Gansu Province, and Baoji and Luochuan, Shaanxi Province, some common features of the loess-pedostratigraphic development on the Loess Plateau are verified. A comparison between the curves of deep-sea oxygen isotope and magnetic susceptibility of loess within stage 1—5 suggests the continuity of the loess stratigraphy although pedostratigraphic research gives some small interfaces in it. Evident difference in thickness or depositional rate of loess appeared mainly since about 1.7 Ma B. P. The intensity of paleoclimatic information from the loess strata is inversely proportional to the resolution of paleoclimate over the plateau. The intensity increases gradually from NW to SE Loess Plateau, and the resolution vice versa. The paleoclimatic information in the loess strata is composed of two parts: global and regional signals. The gradual increase of signal intensity from NW to SE Loess Plateau is a reflection of the regional signal, and the same cycles of loess （dry-cold period） and paleosol （wet-warm period） in different profiles on the plateau represent the global change of paleoclimate.The variation in frequency-dependent susceptibility (xfd) of loess stratum, i.e. its wave peak and valley is associated regularly with the appearance of paleosol and loess layers in the profiles. It indicates formation of ultrafine-grained （<0.03μm） ferromagnetic minerals in the pedogenic processes, which may be the most important factor for higher susceptibility of paleosol than loess. The content of the ultrafine-grained magnetic minerals reflects the warm and humid degree of the paleoclimate. The frequency-dependent susceptibility has a clear implication for paleoclimate. It is sensitive for the slight variation of paleoclimate, and provides an important information on the paleoclimatic （gradual or sudden） change. |
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