SUMMARY Further studies of gyroremanent magnetisation (GRM) and rotational remanent magnetisation (RRM) have been conducted on lake sediments from the Zoige Basin in the Eastern Tibetan Plateau, in which greigite is the main carrier of gyroremanent magnetisation. Greigite has the greatest effective gyrofield (Bg) of all magnetic minerals studied so far, being several hundred µT for a peak AF of 80 mT. This high Bg value has the potential to be used as an indicator for greigite. The GRM produced during static alternating field (AF) demagnetisation became close to its maximum at a peak AF of 150 mT. Attempts to extract the natural remanent magnetisation (NRM) by algebraic elimination of the GRM were unsuccessful above fields of about 30 mT because the GRM became much larger than the remaining NRM. The GRM of a crushed sample was much reduced because of the destruction of the sample's anisotropy, although as expected, both RRM and Bg were similar before and after crushing, thus demonstrating that RRM and Bg are independent of anisotropy. Measurement of the anisotropy of two samples from different depths showed that the deeper sample, which acquired the higher GRM, also had the higher anisotropy presumably as a result of greater sediment compaction. Study of anisotropy of GRM may help to elucidate the preferred alignment of greigite within the sample, which is difficult to ascertain by other means.
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Hu et al. (2002) studied this question.
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