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

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 ( 10 Be flux) and marine (i.e., relative paleointensity and authogenic 10 Be/ 9 Be 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 highresolution chronological correlation to marine and ice core records, only if the potential lock-in effect can be precisely determined.

Problems of magnetostratigraphy of Pleistocene loess-soil deposits of the South of Ukraine

“…При большой глуби-не фиксации (первые метры), согласно пред-ложенной В. А. Большаковым схеме, вариации направления намагниченности, отражающие изменения магнитного поля, должны быть су-щественно сглажены или вообще исчезнуть. Возможность такого влияния на палеомагнит-ную запись показана на примере изучения гео-магнитных экскурсов [Zhu et al, 1994б, 2007Fang et al, 1997;Sun et al, 2013], запись кото-рых сглаживалась или удревнялась в зонах раз-витого педогенеза. Тем не менее резкие изме-нения вектора остаточной намагниченности в записях экскурсов, обнаруженные в лессовых горизонтах [Zhu et al, 1994б, 2007Sun et al, 2013], а также выделение вековых геомагнит-ных вариаций [Evans, Heller, 2001] указывают на намного меньшую глубину фиксации для лессов по сравнению с почвами.…”

A sedimentary paleomagnetic record of the upper Jaramillo transition from the Lantian Basin in China

“…This is supported by an investigation of the timing and lock-in effect of the Laschamp geomagnetic excursion in Chinese loess, which indicated a progressive southeastward increase in the lock-in depth in three loess sections across the CLP (Sun et al 2013). Complicated regional geology and paleoenvironmental backgrounds, such as frequent tectonic activity (Sun 2005) and water content in loess (Wang and Løvlie 2010;Zhao and Roberts 2010), might play a significant role during deposition and final consolidation of aeolian dusts.…”

“…the Weinan and Yushan loess sections (Fig. 9), and might result from different postdepositional remanent magnetization processes induced by varying sedimentary characteristics and environments from area to area (Sun et al 2013). Moreover, the duration of the reversal determined by a very limited number of specimens from this study, ca.…”

“…Additionally, numerous studies have focused on the exact identification and/or detailed processes of geomagnetic reversals (Heller and Liu 1982;Sun et al 1993;Zhu et al 1994;Spassov et al 2001Spassov et al , 2003Pan et al 2002;Liu et al 2008;Yang et al 2005Yang et al , 2014Liu 2010, 2011b;Wang et al 2014;Zhao et al 2014;Zhou et al 2014) and excursions (Zhu et al 1998Fang et al 1997;Pan et al 2002;Yang et al 2004Yang et al , 2007aYang et al , 2007bYang et al , 2008Jin et al 2012;Sun et al 2013) recorded in Chinese loess.…”

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

“…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).…”