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

Abstract

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.