HR: 1340h
AN: GP53B-1212    [Abstracts]
TI: On detection of small changes in frequency-dependent magnetic susceptibility of weakly magnetic sediments: implications for magnetic granulometry
AU: Chadima, M
EM: chadima@sci.muni.cz
AF: Institute of Geology, Academy of Sciences of the Czech Republic, v.v.i., Rozvojova 269, Praha, CZ-16500, Czech Republic
AU: Chadima, M
EM: chadima@sci.muni.cz
AF: Agico Inc., Jecna 29a, Brno, CZ-62100, Czech Republic
AU: Kadlec, J
EM: kadlec@gli.cas.cz
AF: Institute of Geology, Academy of Sciences of the Czech Republic, v.v.i., Rozvojova 269, Praha, CZ-16500, Czech Republic
AU: Pokorny, J
EM: jpokorny@agico.cz
AF: Agico Inc., Jecna 29a, Brno, CZ-62100, Czech Republic
AU: * Hrouda, F
EM: fhrouda@agico.cz
AF: Agico Inc., Jecna 29a, Brno, CZ-62100, Czech Republic
AB: The frequency-dependent magnetic susceptibility is one of the useful tools for magnetic granulometry diagnostics. However, the instrumentation common in environmental research does not enable measuring the frequency-dependent susceptibility with sufficient precision, in magneticaly weak sedimentary rocks. Recently, the MFK1-FA Kappabridge was developed that enables such measurements much more precisely. The instrument measures the susceptibility in variable fields and at three operating frequencies, viz. 976 Hz, 3,904 Hz and 15,616 Hz, the field ranges being 2 to 700 A/m at 976 Hz, 2 to 350 A/m at 3,904 Hz and 2 to 200 A/m at 15,616 Hz. A collection of Late and Middle Pleistocene loess and paleosol samples and Late Holocene cave deposits was collected, with bulk susceptibility being about 1 x 10-4 [SI], and the frequency-dependence (defined as difference between susceptibilities measured at the lowest and highest frequencies normed by the measured value) ranging from 1% to about 10%. The collection was measured 5 times, each collection measurement being executed in different day; the instrument was newly calibrated in each measuring day. The differences between individual specimens were evaluated statistically. It was revealed that the variation in the frequency-dependence in the order of 1% is well reproducible and the measurements can be interpreted in terms of magnetic granulometry even in the weakly magnetic sedimentary horizons. The trends obtained are verified through the investigation using the method of time-dependent IRM.
DE: 1512 Environmental magnetism
DE: 1519 Magnetic mineralogy and petrology
DE: 1540 Rock and mineral magnetism
DE: 1594 Instruments and techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting