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A lock-in model for the complex Matuyama-Brunhes boundary record of the loess/palaeosol sequence at Lingtai (Central Chinese Loess Plateau)

Spassov, S. ; Heller, F. ; Evans, M. E. ; Yue, L. P. ; Dobeneck, T. von

In: Geophysical Journal International, 2003, vol. 155, no. 2, p. 350-366

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    Title
    • A lock-in model for the complex Matuyama-Brunhes boundary record of the loess/palaeosol sequence at Lingtai (Central Chinese Loess Plateau)
    Author
    • Spassov, S.. Institut für Geophysik, ETH Zürich, CH-8093 Zürich, Switzerland. E-mail: simo.spassov@mag.ig.erdw.ethz.ch
    • Heller, F.. Institut für Geophysik, ETH Zürich, CH-8093 Zürich, Switzerland. E-mail: simo.spassov@mag.ig.erdw.ethz.ch
    • Evans, M. E.. Institute for Geophysical Research, University of Alberta, T6G 2J1, Edmonton, Alberta, Canada
    • Yue, L. P.. Department of Geology, Northwest University, 710 069 Xi'an, Shaanxi Province, China
    • Dobeneck, T. von. Fachbereich Geowissenschaften, Universität Bremen, Postfach 320440, D-283334 Bremen, Germany
    Document Type
    • Postprint
    OAI-PMH Identifier
    • oai:doc.rero.ch:300110
    Summary
    In most marine sedimentary records, the Matuyama-Brunhes boundary (MBB) has been found in interglacial oxygen isotope stage 19. In the magnetostratigraphic records of most Chinese loess/palaeosol profiles the MBB is located in loess layer L8, which was deposited during a glacial period. The MBB at Lingtai (central Chinese Loess Plateau) also occurs in L8 and is characterized by multiple polarity flips. The natural remanent magnetization is mainly carried by two coexisting components. The higher coercivity (harder) component dominates in loess layers and is thought to be of detrital origin. The lower coercivity (softer) component prevails in palaeosols and was most probably formed in situ by (bio-)chemical processes. A lock-in model for the Lingtai MBB record has been developed by extending the lithologically controlled PDRM model of Bleil & von Dobeneck (1999). It assumes two lock-in zones. The NRM of the magnetically harder component is physically locked by consolidation shortly after loess deposition, whereas the softer component is formed at greater depth by pedogenesis and acquires a chemical remanent magnetization of younger age. At polarity boundaries, grains carrying reversed and normal directions may therefore occur together within a single horizon. The model uses ARM coercivity spectra to estimate the relative contributions of the two components. It is able to explain the observed rapid multiple polarity flips and low magnetization intensities as well as the stratigraphic shift of the Lingtai MBB with respect to the marine records