柴达木盆地大红沟剖面新生代地层岩石磁学特征与环境演变

摘要

通过对柴达木盆地大红沟剖面新生代沉积物岩石磁学的研究,探讨青藏高原东北部的构造活动与气候变化.典型样品的热退磁曲线表明,磁铁矿含量随地层年代的变新而增大.沉积物的磁化率由老至新划分为5个阶段,随时代变新而不断增大,与磁铁矿含量的增大相吻合.柴达木盆地沉积物磁化率值的变化与气候变化关系密切:①约43Ma,磁化率增大是全球气候变冷变干导致沉积物中磁铁矿含量增加所致;②约33Ma,磁化率增大是全球气候加速变冷的结果;③22Ma左右,青藏高原整体隆升,控制中国大陆环境的气候系统由行星风系转变为季风风系,亚洲内陆开始干旱化,致使更多的磁铁矿得以保存,磁化率值再度增大;④14Ma青藏高原东北缘发生区域构造抬升,西北干旱区进一步扩大,东亚季风明显加强,同时全球冰量扩张,导致柴达木盆地沉积物的磁化率整体增大,而且波动幅度和频率增大.%This paper has discussed the climate change in northeastern Tibetan Plateau according to the Cenozoic rock magnetic characteristics of the Dahonggou section in Qaidam Basin. Progressive thermal demagnetization of typical samples indicates that the percentage composition of magnetite increases with the strata getting younger. The sediments in Qaidam Basin exhibit a noticeable increase in magnetic susceptibility by 5 stages, which is coincident with the increase in the percentage composition of magnetite. The change of magnetic susceptibility of sediments in Qaidam Basin was closely related to climate change: ①the increase in magnetic susceptibility at about 43Ma resulted from the climate cooling and drying; ② the increase in magnetic susceptibility at 33Ma or so resulted from the global climate cooling; ③the tectonic uplift of the Tibetan Plateau at about 22Ma resulted in the climate system thatrncontrolled China's continental environment change from the planetary system of winds to the monsoon of winds and also caused aridi-fication in Asian inland. Hence the magnetite was preserved and the magnetic susceptibility increased; ④the regional tectonic uplift in northeastern Tibetan Plateau at about 14Ma resulted in the expansion of the western arid region and the intensification of eastern Asian monsoon. Meanwhile, the global ice volume extended. Therefore, the magnetic susceptibility of the sediments in Qaidam Basin rose and the fluctuation range and frequency increased.