American Geophysical Union Become an AGU Member
Subscribe to AGU Journals		 AGU Home AGU Publications

Read Full Article (file size: 2411023 bytes)    Cited by

GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, VOL. 6, Q06H18, doi:10.1029/2004GC000901, 2005

Remagnetization of Quaternary eolian deposits: A case study from SE Chinese Loess Plateau

Xisheng Wang

Institute of Geomechanics, Chinese Academy of Geological Sciences, 11 Minzu Xueyuan Nanlu, Beijing, 100081, China


Reidar Løvlie

Department of Earth Science, University of Bergen, Allegt. 41, Bergen, N-5007 Norway


Zhenyu Yang

Department of Earth Sciences, Nanjing University, Nanjing, 210093, China


Junling Pei

Institute of Geomechanics, Chinese Academy of Geological Sciences, 11 Minzu Xueyuan Nanlu, Beijing, 100081, China


Zhizhong Zhao

Institute of Geomechanics, Chinese Academy of Geological Sciences, 11 Minzu Xueyuan Nanlu, Beijing, 100081, China


Zhiming Sun

Institute of Geomechanics, Chinese Academy of Geological Sciences, 11 Minzu Xueyuan Nanlu, Beijing, 100081, China


Abstract

The loess-paleosol succession in the southeastern margin of the Chinese Loess Plateau retains high-resolution archives of sedimentary and environmental change. In this study, we report a detailed paleomagnetic and rock magnetic investigation of loess-paleosol sequences in the Sanmenxia area spanning the last 1.1 Myr. The results demonstrate that the Matuyama/Brunhes Boundary occurs at the top of soil S8 and the upper and lower boundaries of the Jaramillo Normal Subchron are encountered at the top of soil S10 and loess L13, respectively, in agreement with the classic Luochuan section. Loess L9, also referred to as “the upper sand layer,” is the coarsest loess unit over the last 1.1 Myr and carries an “imperfect” normal polarity magnetization. Although it is fully separated by a short reversed polarity interval, this thick normal polarity zone is too extensive to represent excursions like Kamikatsura and/or Santa Rosa and is concluded to represent an artifact rather than a record of geomagnetic field directions. Precise multiparameter environmental magnetic determination reveals that the short reversed polarity interval within the middle of this thick normal polarity zone exactly corresponds to a thin pedogenic horizon. Detailed rock magnetic analyses show that there are no intrinsic differences in magnetomineralogical properties between this pedogenic interval and other parts of L9, although the composition of magnetically soft components (magnetite/maghemite) in the short pedogenic interval is relatively higher than that of other parts of L9. Thus it is proposed that extensive remagnetization of parts of L9 most likely reflects a lithology-dependent process, and the dramatic coarsening of particle size across L9 is the fundamental reason for pervasive remagnetization. Our magnetostratigraphic results strongly imply that we need to reconsider the remanence-recording fidelity of coarse loess (L9, and probably L15) and care should be taken to interpret excursions in future paleomagnetic investigations of the Chinese loess.

Received 21 December 2004; accepted 26 April 2005; published 22 June 2005.

Keywords: Chinese Loess Plateau; excursion; remagnetization.

Index Terms: 1599 Geomagnetism and Paleomagnetism: General or miscellaneous; 1520 Geomagnetism and Paleomagnetism: Magnetostratigraphy; 1533 Geomagnetism and Paleomagnetism: Remagnetization.

Read Full Article (file size: 2411023 bytes)    Cited by

Citation: Wang, X., R. Løvlie, Z. Yang, J. Pei, Z. Zhao, and Z. Sun (2005), Remagnetization of Quaternary eolian deposits: A case study from SE Chinese Loess Plateau, Geochem. Geophys. Geosyst., 6, Q06H18, doi:10.1029/2004GC000901.