Reconstruction of 130-kyr Relative Geomagnetic Intensities from ¹⁰Be in Two Chinese Loess Sections

Abstract

ABSTRACT. Efforts to extract weak geomagnetic excursion signals from Chinese loess-paleosol 10 Be have generally been unsuccessful due to the complexities of its accumulation, because the geomagnetic and climate (precipitation and dust) signals contained in loess-paleosol sequence are tightly overprinted. Here, we present a reconstruction of geomagnetic relative paleointensities for the past 130 kyr from 10 Be records in 2 Chinese loess-paleosol sections using a correction based on the correlation of 10 Be with magnetic susceptibility (SUS) to remove the climatic contamination. Both these records reveal the Laschamp and Blake events, which lie in the loess and paleosol (L 1 SS 1 and S 1 SS 3 ) horizons corresponding to mid-MIS 3 and 5e, respectively. The good agreement between our results and other geomagnetic intensities reconstructions from Atlantic and Pacific sediments indicates that our method is robust. Our study suggests the potential application of loess-paleosol 10 Be for reconstructing geomagnetic intensity variations spanning the whole Quaternary.

A paleomagnetic record in loess–paleosol sequences since late Pleistocene in the arid Central Asia

“…Moreover, lockin depths seem to cause increasing problems toward the southeastward direction on the CLP where certain excursion is missing or poorly captured in most sections (Sun et al 2013). Recently, with the aid of cosmogenic nuclides analysis (Zhou et al 2010), reassessment of the BGE and LGE excursions in some of the classic sections on the CLP revealed a record of geomagnetic intensity that is consistent with the record in marine sediments, thus affirming the potential value of geomagnetic excursions as important chronological markers in Quaternary sediments.…”

“…The BGE and LGE are two important geomagnetic markers in the Brunhes epoch and have been widely revealed in the loess-paleosol sequences via paleomagnetic (Zheng et al 1995;Zhu et al 1994Zhu et al , 1999Zhu et al , 2006Fang et al 1997;Sun et al 2013) and cosmogenic nuclide ( 10 Be) methods (Zhou et al 2010) since the seminal work in the 1980s (Liu 1985). In spite of the wide report in the CLP, the complete BGE record was first revealed in the Xining loess section (Fig.…”

“…Although the RPIs were introduced in the study of geomagnetic excursion in loess, the recovery of continuous RPI via paleomagnetic measurements has proved to be complex due to the post-depositional alteration during strong pedogenesis (Pan et al 2002;Yang et al 2007Yang et al , 2012. Recently, based on the cosmogenic 10 Be concentration, the RPI curves have been reconstructed in typical loess sections in the CLP (Zhou et al 2010), offering a continuous RPIs in the CLP since last interglacial. Figure 10 shows the comparison of our record with certain global and regional RPI stacks.…”

“…As an important terrestrial archive, loess deposits in the Chinese Loess Plateau (CLP) also clearly contain anomalous directions related to the LGE (Zhu et al 1999(Zhu et al , 2006Zhou et al 2010;Sun et al 2013) and BGE (Zhu et al 1994;Zheng et al 1995;Fang et al 1997;Zhou et al 2010). However, the timing and duration of the excursions recorded in the loess sections are not well determined because remanence acquisition is possibly influenced by post-depositional processes (Roberts and Winklhofer 2004;Sun et al 2013).…”

Preliminary study of 10 Be/ 7 Be in rainwater from Xi’an by Accelerator Mass Spectrometry

“…The Xi'an AMS Center has focused on tracing geomagnetic field changes with 10 Be in loess [14] [20,21], reconstructing paleoprecipitation [22], and exposure/burial chronology [23]. These studies require high precision 10 Be measurements from the Xi'an AMS instrument.…”