中国黄土磁性地层研究进展与展望

Progress and outlooks on magnetostratigraphy of Chinese loess

  • 摘要: 中国黄土是最重要的第四纪陆相气候记录之一,磁极性地层是建立第四纪黄土年代框架的主要方法之一。本文总结了中国黄土所记录的布容/松山(Brunhes/Matuyama)、加拉米诺(Jaramillo)、奥尔都维(Olduvai)和松山/高斯(Matuyama/Gauss)等几个作为主要定年依据的极性倒转界限的研究结果,并将黄土记录的这些界限位置与深海记录进行了对比。结果发现,不同黄土剖面所记录的各地磁极性倒转界限的位置并不一致,其差异可超过一个黄土-古土壤旋回,且不能用lock-in效应、气候和沉积速率差异、黄土地层划分差异来解释。这些地磁极性界限位置的差异指示极性界限附近的黄土可能经历了不同程度的重磁化。同时,这些差异也导致了不同研究者基于磁极性地层所建立的轨道尺度的黄土年代标尺与深海氧同位素记录的对比存在较大分歧。未来对黄土所记录的地磁场相对古强度(RPI)的研究可望为识别极性倒转界限的真实位置提供依据,并最终解决中国黄土与深海记录轨道尺度对比方案的分歧。

     

    Abstract: The Chinese loess is one of the most important terrestrial records of the Quaternary climate changes. Magnetostratigraphy is one of the primary methods for establishing the chronological framework of the Quaternary loess. The measured positions of the Brunhes/Matuyama, Jaramillo, Olduvai, and Matuyama/Gauss polarity reversal boundaries in Chinese loess were summarized and compared against corresponding marine records. It was found that the positions of each polarity reversal boundary are inconsistent among different loess sections, and the difference spanned more than one loess-paleosol cycle. This discrepancy cannot be attributed to the lock-in effect, regional climate, sedimentation rate or different loess stratigraphic divisions. This may indicate that the polarity reversal boundaries recorded by loess deposits had probably experienced significant remagnetization, leading to a large discrepancy between loess geochronometer in magnetostratigraphy at orbital scale and marine oxygen isotope records by different researchers. In the future, studies shall focus more on the relative paleointensity (RPI) of loess to confirm the true position of each polarity reversal boundary and ultimately resolve the discrepancy in the comparison scheme between Chinese loess data and deep-sea sediment record.

     

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