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Pedogenesis and its effects on natural remanent magnetization acquisition history of the Chinese loess/paleosol sequences Presenter: Qingsong Liu Supervisors: Subir K. Banerjee Michael J. Jackson Outline Introduction of the Chinese loess Magnetic carriers of loess ChRM
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Pedogenesis and its effects on natural remanent magnetization acquisition history of the Chinese loess/paleosol sequences
Presenter: Qingsong Liu
Supervisors: Subir K. Banerjee
Michael J. Jackson
Distribution of loess (wind-blown sediments) in central China (Kukla et al., 1988)
SPECMAP oxygen-isotope record tuned chronology compared to magnetic susceptibility (Kukla et al., 1988)
Depth plots of magnetic susceptibility in Xifeng and Luochuan compared to SPECMAP oxygen-isotope record (Kukla et al., 1988)
Depth plots of paleomagnetic records of Matuyama-Brunhes (a) and Jaramillo (b) recorded at Weinan (Zhu et al., 1994)
Problems of paleoclimatic and paleomagnetic signals recorded by the Chinese loess
1. Ambiguities in interpreting paleoclimatic signals
A conceptual model of the relationship between magnetic susceptibility and the amount of precipitation (after Liu et al., 1999)
2. Puzzle of the Matuyama/Brunhes boundary recorded by loess and marine sediments (Zhou et al., 1999)
The Jiuzhoutai (JZT) section is located near Lanzhou City (36oN/103o50E), and the Yuanbao (YB) section (35o38N/103o10E) is in the Linxia Basin
The mean annual temperature at these two sites is similar, at about 6-7oC. In contrast, the mean annual precipitation at YB (~500 mm) is higher than at JZT (300-400 mm). Therefore, YB has higher degree of pedogenesis than JZT.
Aeolian magnetite (DRM)
Pedogenic maghemite (CRM)
Problem: it is a mixture
Traditional method for isolating the characteristic remanent magnetization (ChRM)
**ChRM does not equal primary RM !
Thermal demagnetization has been widely used to get ChRM by heating samples to 300-350oC
What is the carrier of ChRM? magnetite (aeolian) or maghemite (pedogenic) ?
Traditional methods can not solve this problem because they worked on bulk information, which reflect an assemblage of magnetic minerals.
Our new approach
We use low-temperature cycle (LTC) to directly measure the magnetic carrier of ChRM
Coarse-grained pseudo single domain (PSD and multi-domain (MD) magnetite (> several hundreds nm)
Single-domain (SD) magnetite (~20-50 nm)
Behavior of remanences carried by magnetite and maghemite during LTC
One of the dramatic effects is that the magnetic particles become magnetically harder, namely increasing the remanence coercivity.
Is the aeolian magnetite partially oxidized?
Temperature dependence of hysteresis parameters for a representative loess sample
Measured at room-T
Aeolian magnetites in loess samples are partially oxidized with much higher remanence coercivity than the fine-grained pedogenic maghemite particles.
Therefore, the distinguished coercivity spectra between these two kinds of particles permit us to use AF demagnetization to separate their remanences
RPI=NRM/ (normalization parameter)
Normalization parameters: susceptibility, ARM and SIRM
Which one is a better parameter for RPI?
Comparison of depth plots of magnetic susceptibility of the JZT and YB profiles and the previous interpretation of pedostratigraphy
I thank my supervisors Prof. Subir Banerjee and Dr. Michael Jackson.
I also thank the the other IRMer for their helps during the past 5 years. They are Bruce Moskowitz, Peter Solheid, Jim Marvin, Thelma de Souza Berquo’.
I thank the following persons for their helpful suggestions and co-operations on my research: David Dunlop, Ozden Ozdemir, Yongjae Yu, Lisa Tauxe, Barbara Maher, Andrew Roberts, Jose Torrent, Fahu Chen, Rixiang Zhu, Yongxin Pan and Chenglong Deng.
I thank my friends at twin cities: Xianfeng Wang, Fu Qi, Qing Zhang, Jim Thill.
My last thank is given to My wife, Qiong Lin.