Preliminary study on the mineral magnetic properties of sediments from K?lna Cave (Moravian Karst), Czech Republic |
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Authors: | P ?roubek J F Diehl J Kadlec K Valoch |
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Institution: | (1) Department of Geological Engineering and Sciences, Michigan Technological University, 49931 Houghton, MI, USA;(2) Czech Geological Survey, Klárov 3, 118 21 Prague 1, Czech Republic;(3) Moravian Museum, Zelny Trh 6, 659 37 Brno, Czech Republic |
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Abstract: | Summary Magnetic property variations in marine, lacustrine and loess-paleosol sequences have proved to be useful proxies in climate
change studies. However in order to correctly interpret the record of the magnetic property variations it is absolutely necessary
to have a good understanding of the cause of the observed variations. Most of the ambiguity in loess-paleosol studies is in
distinguishing the role of pedogenesis from other climatic factors. Studying the mineral magnetic properties of the protected
cave sediments which have not undergone pedogenesis allows us to determine the degree to which detrital input is climatically
driven. These results will help us better understand the variations observed in the surficial loess-paleosol sequences.
This study reports mineral magnetic data collected from entrance facies sediments deposited during the early Wurmian glacial
stage in the Kůlna Cave. The entrance facies sediments consist of loess-like silts with varying amount of talus. The magnetic
susceptibility record from these sediments shows higher values in layers originating in colder climates which is different
to that commonly observed in surficial loess deposits. Higher values of magnetic susceptibility in Kůlna sediments are probably
due to higher concentrations of ferromagnetic minerals (magnetite and maghemite) and due to an increased proportion of superparamagnetic
grains. The magnetic mineralogy and the grainsize distribution (grains larger than superparamagnetic) appear not to change
throughout the studied profiles. Higher magnetic susceptibility accompanied by an increase in the superparamagnetic fraction
observed in the sediments deposited during colder periods can be explained by an increased input from a pedogenic source when
the vegetation cover was reduced and the erosion rate increased. |
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Keywords: | climate paleoenvironment magnetic grainsize magnetic mineralogy last glacial eolian sediments |
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