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Paleoclimatic Significance of the Mineral Magnetic Record of the Chinese Loess and Paleosols

Published online by Cambridge University Press:  20 January 2017

Barbara A. Maher  and
Roy Thompson
Barbara A. Maher
Affiliation:
School of Environmental Sciences, University of East Anglia, Norwich, United Kingdom
Roy Thompson
Affiliation:
Department of Geology and Geophysics, University of Edinburgh, United Kingdom
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Abstract

The origins of the magnetic susceptibility variations of the Chinese loess and paleosols are explored by scanning and transmission electron microscopy of magnetic extracts, and by magnetic modeling of magnetic hysteresis data, to provide quantified estimates of the major magnetic components. Microscopy identifies several distinct size and shape characteristics in the magnetic carriers. Lithogenic magnetites, intact and abraded, dominate the coarse-grained magnetic fraction. The smallest of the coarse grains is ∼ 2 μm. The remaining magnetic materal is ultrafine in size, with two types of magnetite particles present. Type A particles strongly resemble soil magnetites produced by inorganic precipitation. Type B particles, which occur rarely, are probably bacterial in origin. Quantitative modeling of these magnetic assemblages shows that over 90% of the susceptibility variations is accounted for by the superparamagnetic magnetite component. Compared to the loess units, the paleosols are richer in magnetite, particularly of superparamagnetic size, and have a threefold higher ratio of magnetite to hematite. We identify pedogenic formation of magnetite as the major contributor to the loess magnetic record. Matching this record against other paleoclimatic records, we find an extremely high correlation with the standard 18O record. The Chinese loess sequences record a very high resolution magnetic stratigraphy directly related to changing climate.

Type
Research Article
Information
Quaternary Research , Volume 37 , Issue 2 , March 1992 , pp. 155 - 170
Copyright
University of Washington

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