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Links between bulk sediment particle size and magnetic grain‐size: general observations and implications for Chinese loess studies
Author(s) -
OLDFIELD FRANK,
HAO QINGZHEN,
BLOEMENDAL JAN,
GIBBSEGGAR ZOË,
PATIL SHIVA,
GUO ZHENGTANG
Publication year - 2009
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/j.1365-3091.2009.01071.x
Subject(s) - geology , loess , remanence , ferrimagnetism , grain size , environmental magnetism , pedogenesis , superparamagnetism , mineralogy , particle size , single domain , magnetic mineralogy , sediment , geomorphology , magnetization , magnetic domain , paleontology , soil science , soil water , physics , magnetic field , quantum mechanics
Using a combination of particle size analysis, magnetic measurements, scanning electron microscopy and transmission electron microscopy imaging, this study shows that in a wide range of depositional environments, there is a strong link between particle size classes and magnetic response, especially below the upper limit of stable single domain magnetic behaviour. Ferrimagnetic grain assemblages dominated by stable single domain magnetosomes regularly have peak susceptibility and remanence values in coarser grades than do those containing finer‐grained, viscous and superparamagnetic secondary magnetic minerals formed during pedogenesis. This effect is despite the fact that there is a one to two orders of magnitude size difference between the particle size boundaries (at 1 or 2 μm) and key domain state transitions (mostly below 0·05 μm). The implications of these results are explored using samples spanning 22 Myr of loess accumulation on the Chinese Loess Plateau. The results from the loess sections, complemented by data from low‐temperature magnetic experiments, show that there are subtle distinctions in mean ferrimagnetic grain‐size between the Pleistocene and Miocene parts of the record, thus allowing more refined rock magnetic interpretations of the fine‐grained ferrimagnetic mineral assemblages arising from the effects of weathering, pedogenesis and possibly diagenesis in the sections studied.