Timing and lock-in effect of the Laschamp geomagnetic excursion in Chinese Loess

Authors

  • Youbin Sun,

    Corresponding author
    1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China
    2. Institute of Global Environmental Change, Xi'an Jiaotong University, Xi'an, China
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  • Xiaoke Qiang,

    1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China
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  • Qingsong Liu,

    1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
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  • Jan Bloemendal,

    1. Department of Geography and Planning, University of Liverpool, Liverpool, UK
    2. 2011 Cooperative Innovation Center for Arid Environment and Climate Changes, Lanzhou University, Gansu, China
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  • Xulong Wang

    1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China
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Abstract

[1] The Laschamp geomagnetic excursion (LGE, at ∼41 ka) is a critical age control for hemispherical comparison of paleoclimate records from various kinds of geological archives (e.g., ice core, marine, and lake sediments). The timing of the LGE in Chinese Loess, however, remains poorly constrained due to the lack of a reliable chronology and the complex acquisition processes of natural remanent magnetization. Here, we systematically compare the paleomagnetic results of three optically stimulated luminescence dated loess sequences on the Chinese Loess Plateau. Our results indicate that the timing of the LGE in the northwestern Loess Plateau is slightly older than the absolute radiometric age determination and the timing inferred from Greenland ice core (10Be flux) and marine (i.e., relative paleointensity and authogenic 10Be/9Be stack) records, but younger than the counterparts in the central Loess Plateau. We attribute the different timing of the LGE in the three loess sections to a progressive southeastward increase in the lock-in depth caused by the combined effects of postdepositional processes (e.g., surface mixing, chemical weathering, and lock-in delay) on the remanence acquisition process. We conclude that caution is needed to use the LGE in Chinese Loess as a reliable tie-event for high-resolution chronological correlation to marine and ice core records, only if the potential lock-in effect can be precisely determined.

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