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2800 km2 area in north-eastern Bulgaria. The main pollution sources are several plants of chemical industry (soda production, polymers, fertilizers), cement plant and power plants. Pollutants emitted as a result of these industrial productions do not contain as much magnetic fraction in order to cause extreme magnetic enhancement of top-soils, which is a typical feature for the metallurgical industries, mining, coal-burning power plants. A new approach is proposed to correct the data (field and laboratory) for the effect of different soil types in the area, which is not a negligible factor in such case. As a result, more precise lateral distribution of the anthropogenic magnetic fraction is obtained, delineating all affected by pollution regions. The efficiency of the newly proposed method for taking into account differences in soil types is validated through correlation analysis between magnetic parameters and heavy metal content in selected samples. Correlation between the corrected magnetic susceptibility values, Co, Ni, As, Pb and the Enrichment Factors (EF = ∑Ci/Ck, Ci — measured concentrations of Pb, Zn, Cu, Co, Ni, As; Ck — background concentrations for the corresponding elements) increase after the applied correction.
doi:10.1016/S0031-9201(03)00063-3 
Copyright © 2003 Elsevier Science B.V. All rights reserved.
Inter-laboratory calibration of low-field magnetic and anhysteretic susceptibility measurements
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Leonardo Sagnotti
, 
, a, Pierre Rochetteb, Mike Jacksonc, Fabienne Vadeboinb, Jaume Dinarès-Turella, Aldo Winkler and “Mag-Net” Science Team1a
Received 25 October 2002;
Abstract
Inter-laboratory and absolute calibrations of rock magnetic parameters are fundamental for grounding a rock magnetic database and for semi-quantitative estimates about the magnetic mineral assemblage of a natural sample. Even a dimensionless ratio, such as anhysteretic susceptibility normalized by magnetic susceptibility (Ka/K) may be biased by improper calibration of one or both of the two instruments used to measure Ka and K. In addition, the intensity of the anhysteretic remanent magnetization (ARM) of a given sample depends on the experimental process by which the remanence is imparted. We report an inter-laboratory calibration of these two key parameters, using two sets of artificial reference samples: a paramagnetic rare earth salt, Gd2O3 and a commercial “pozzolanico” cement containing oxidized magnetite with grain size of less than 0.1 μm according to hysteresis properties. Using Gd2O3 the 10 Kappabridges magnetic susceptibility meters (AGICO KLY-2 or KLY-3 models) tested prove to be cross-calibrated to within 1%. On the other hand, Kappabridges provide a low-field susceptibility value that is ca. 6% lower than the tabulated value for Gd2O3, while average high-field susceptibility values measured on a range of instruments are indistinguishable from the tabulated value. Therefore, we suggest that Kappabridge values should be multiplied by 1.06 to achieve absolute calibration. Bartington Instruments magnetic susceptibility meters with MS2B sensors produce values that are 2–13% lower than Kappabridge values, with a strong dependence on sample centering within the sensor. The Ka/K ratio of ca. 11, originally obtained on discrete cement samples with a 2G Enterprises superconducting rock magnetometer and a KLY-2, is consistent with reference parameters for magnetites of grain size <0.1 μm. On the other hand, Ka values from a 2G Enterprises magnetometer and K values from a Bartington Instruments MS2C loop sensor for u-channel and discrete cement samples, will produce average Ka/K values that are unrealistically high if not properly corrected for the nominal volume detected by the sensors for these instruments. Inter-laboratory measurements of K and Ka for standard paleomagnetic plastic cubes filled with cement indicate remarkable differences in the intensity of the newly produced ARMs (with a standard deviation of ca. 21%), that are significantly larger than the differences observed from the calibration of the different magnetometers employed in each laboratory. Differences in the alternating field decay rate are likely the major source of these variations, but cannot account for all the observed variability. With such large variations in experimental conditions, classical interpretation of a “King plot” of Ka versus K would imply significant differences in the determination of grain size of magnetite particles on the same material.
Author Keywords: Rock magnetism; Magnetic susceptibility; Anhysteretic remanent magnetization; Calibration; Instrumentation; Relative paleointensity
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1 Barbara Maher, Eva Moreno: University of Lancaster, UK; Monika Hanesch, Robert Scholger: University of Leoben, Austria; Robert Jude, John Shaw: University of Liverpool, UK; Gregg McIntosh, Maria Luisa Osete: University of Madrid, Spain; Jürgen Matzka, Nikolai Petersen: Ludwig-Maximilians-Universität München, Germany; Juan Cruz Larrasoaña, Matthew O’Reagan, Andrew P. Roberts: University of Southampton, UK; Tom Mullender, Clare Peters: University of Utrecht, The Netherlands; Kais J. Mohamed, Daniel Rey: University of Vigo, Spain; Jacqueline Hannam, Friedrich Heller: Institut für Geophysik, ETH Zürich, Switzerland; Thomas Frederichs, Ulrich Bleil: University of Bremen, Germany.
