Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999geoji.138..520j&link_type=abstract
Geophysical Journal International, Volume 138, Issue 2, pp. 520-532.
Astronomy and Astrophysics
Astronomy
6
Bulgaria, Magnetic Susceptibility, Mineral Magnetism, Palaeoclimate
Scientific paper
A detailed record of mineral magnetic properties of a loess-palaeosol profile comprising seven loess horizons, six interbedded palaeosols and recent soil at the top in NE Bulgaria is analysed. A strong contrast between the soil and loess susceptibilities as well as other concentration-dependent hysteresis parameters is present, similar to the well-documented magnetic characteristics of the Chinese loess (Hus & Han 1992; Maher & Thompson 1992; Heller & Evans 1995; Hunt et al. 1995). The magnetic enhancement of the palaeosol units is caused by very fine-grained pedogenic magnetite with superparamagnetic behaviour. Thermomagnetic analyses on bulk material suggest magnetite and maghemite as the main ferrimagnetic carriers in both soil and loess horizons. Their relative proportions are shown to reflect different palaeoclimatic conditions. Chernozem soils, which include recent soil S_0 and first and second palaeosols S_1 and S_2 developed under steppe vegetation, show a high degree of low-temperature oxidation of the pedogenic magnetite to maghemite. This material is characterized by coercive force H_c showing even higher values than those of the parent loess material. The older palaeosols (S_4 to S_6) were formed during more humid climatic conditions and therefore probably developed as forest types. Rock magnetic data suggest the existence here of only partly oxidized magnetite grains. The behaviour of the thermomagnetic curves, characterized by a kink at 200 degC, may be due to either a release of internal stress (built up as a result of partial low-temperature oxidation) or interactions between two phases.
Jordanova Diana
Petersen Nikolai
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