Abstract
Low-temperature oxidation under atmospheric conditions affects the magnetic properties of magnetite in natural rocks: the coercivities of magnetite grains increase and other parameters change accordingly. It was recently shown that heating to 150°C largely removes the effects of low-temperature oxidation (van Velzen and Zijderveld, 1995). Heating may therefore serve as a detection tool for the presence of the effect of low-temperature oxidation.
In the present study, a collection of loess and paleosol samples from various loess regions of the world is examined for the influence of low-temperature oxidation. In all samples of the collection a decrease of coercivities was found after heating to 150°C. Generally loess samples were affected to a larger extent than paleosol samples. The original range of remanent coercivities(B cr)of 21-58 mT changed to 20-42 mT after heating. The IRM capacity of the samples decreased from 0 up to 25%. ARM showed changes between a decrease of 10% and an increase of 15%. The grain-size indicative parameter IRM/ARM is considerably influenced by the heating and therefore by low-temperature oxidation. The changes in susceptibility are limited and will not influence the interpretation of large-scale features of the susceptibility record as a paleoclimate proxy. Small variations, however, may be obscured by the varying influence of oxidation in the outcrop, which can significantly modify the rock-magnetic record.
Rock-magnetic parameters used to determine magnetic mineral content and grain sizes should be corrected for the effect of low-temperature oxidation. To this end heating to 150°C is recommended. The occurrence of the changes is in itself already an indication for the presence of magnetite. Low-temperature oxidation will not only be due to recent weathering in the outcrop, but also to earlier oxidation processes in the source area, during transport and deposition of the loess and during pedogenesis. Truly fresh sediment samples are only influenced by this earlier oxidation. In that case heating will reveal the degree of ancient low-temperature oxidation, which may be related to climate at the time of deposition and pedogenesis.
Similar content being viewed by others
Change history
01 July 2000
An Erratum to this paper has been published: https://doi.org/10.1023/A:1022120822811
References
Appel E., 1987: Stress anisotropy in Ti-rich titanomagnetites. Phys. Earth Planet. Inter., 46, 233–240.
Askill J., 1970: Tracer diffusion data for metals, alloys, and simple oxides, IFI/Plenum Data Corporation, London.
Beske-Diehl S.J. and Soroka W.L., 1984: Magnetic properties of variably oxidized pillow basalt. Geophys. Res. Lett., 11, 217–220.
Chen F.H., Bloemendal J., Wang J.M., Li J.J. and Oldfield F., 1997: High-resolution multi-proxy climate records from Chinese loess: evidence for rapid climatic changes over the last 75 kyr. Palaeogeogr., Palaeoclimatol. Palaeoecol., 130, 323–335.
Dunlop D.J. and Özdemir Ö, 1997: Rock Magnetism: Fundamentals and Frontiers. Cambridge Studies in Magnetism, Cambridge University Press, Cambridge, p573.
Evans M.E. and Heller F., 1994: Magnetic enhancement and palaeoclimate: study of a loess/palaeosol couplet across the loess plateau of China. Geophys. J. Int., 117, 257–264.
Eyre J.K., 1996: The application of high resolution IRM acquisition to the discrimination of remanence carriers in Chinese loess. Studia geoph. et geod., 40, 234–242.
Forster T. and Heller F., 1997: Magnetic enhancement paths in loess sediments from Tajikistan, China and Hungary. Geophys. Res. Lett., 24, 17–20.
Heller F. and Liu T.-S., 1986: Palaeoclimatic and sedimentary history from magnetic susceptibility of loess in China. Geophys. Res. Lett., 13, 1169–1172.
Heller F. and Evans M.E., 1995: Loess magnetism. Rev. Geophys., 33, 211–240.
Hirt A.M., Banin A. and Gehring A.U., 1993: Thermal generation of ferromagnetic minerals from iron-enriched smectite. Geophys. J. Int., 115, 1161–1168.
Housden J. and O'Reilly W., 1990: On the intensity and stability of the natural remanent magnetization of ocean floor basalts. Phys. Earth Planet. Inter., 64, 261–278.
Hunt C.P., Singer M.J., Kletetchska G., TenPas J. and Verosub K.L., 1995: Effect of citrate-bicarbonate-dithionite treatment on fine-grained magnetite and maghemite. Earth Planet. Sci. Lett., 130, 87–94.
Knowles J.E., 1981: The properties of acicular particles of (γ-Fe2O3)x(Fe3O4)1−x. J. Magn. Magn. Mat., 22, 263–2662.
Liu X.-M., Shaw J., Liu T.-S., Heller F. and Baoyin Y., 1992: Magnetic mineralogy of Chinese loess and its significance. Geophys. J. Int., 108, 301–308.
McIntosh G., Rolph T.C., Shaw J. and Dagley P., 1996: A detailed record of normal-reversed-polarity transition obtained from a thick loess sequence at Jiuzhoutai, near Lanzhou, China. Geophys. J. Int., 127, 651–664.
Maher B.A. and Taylor R.M., 1988: Formation of ultrafine-grained magnetite in soils. Nature, 336, 368–371.
Maher B.A. and Thompson R., 1991: Mineral magnetic record of the Chinese loess and paleosols. Geology, 19, 3–6.
Maher B.A. and Thompson R., 1992: Paleoclimatic significance of the mineral magnetic record of the Chinese loess and paleosols. Quat. Res., 37, 155–170.
O'Reilly W., 1984: Rock and Mineral Magnetism, Blackie, Glasgow, p220.
Petersen N. and Vali H., 1987: Observation of shrinkage cracks in ocean floor titanomagnetite. Phys. Earth Planet. Inter., 46, 197–205.
Rutter N., Ding Z.L., Evans M.E. and Wang Y.C., 1991: Baoji-type pedostratigraphic section, loess plateau, north-central China. Quat. Sci. Rev., 10, 1–22.
Smith B.M., 1987: Consequences of the maghemitization of the magnetic properties of submarine basalts: synthesis of previous works and results concerning basement rocks from mainly DSDP legs 51 and 52. Phys. Earth Planet. Inter., 46, 206–226.
Sun W.-W., Banerjee S.K. and Hunt C.P., 1995: The role of maghemite in the enhancement of magnetic signal in the Chinese loess-paleosol sequence: an extensive rock magnetic study combined with citrate-bicarbonate-dithionite treatment. Earth Planet. Sci. Lett., 133, 495–505.
van Oorschot I.H.M. and Dekkers M.J., 1999: Dissolution behaviour of fine-grained magnetite and maghemite in the citrate-bicarbonate-dithionite extraction method. Earth Planet. Sci. Lett., 167, 283–295.
van Velzen A.J. and Zijderveld J.D.A., 1992: A method to study alterations of magnetic minerals during thermal demagnetization applied to a fine-grained marine marl (Trubi formation, Sicily). Geophys. J. Int., 110, 79–90.
van Velzen A.J. and Zijderveld J.D.A., 1995: Effects of weathering on single-domain magnetite in Early Pliocene marine marls. Geophys. J. Int., 121, 267–278.
van Velzen A.J. and Dekkers M.J., 1999: The incorporation of thermal methods in mineral magnetism of loess-paleosol sequences: a brief overview. Chinese Sci. Bull., (in press).
Verosub K.L., Fine P., Singer M.J. and TenPas J., 1993: Pedogenesis and paleoclimate: interpretation of the magnetic susceptibility record of Chinese loess-paleosol sequences. Geology, 21, 1011–1014.
Zhou L.-P., Oldfield F., Wintle A.G., Robinson S.G. and Wang J.T., 1990: Partly pedogenic origin of magnetic variations in Chinese loess. Nature, 346, 737–739.
Rights and permissions
About this article
Cite this article
van Velzen, A.J., Dekkers, M.J. Low-Temperature Oxidation of Magnetite in Loess-Paleosol Sequences: a Correction of Rock Magnetic Parameters. Studia Geophysica et Geodaetica 43, 357–375 (1999). https://doi.org/10.1023/A:1023278901491
Published:
Issue Date:
DOI: https://doi.org/10.1023/A:1023278901491