Magnetic Properties of A Bulgarian Loess/paleosol Profile Related To The Pedogenic Enhancement Model
Abstract
Magnetic susceptibility variations along the loess/palaeosol profile at Lubenovo (Cen- tral North Bulgaria) covering the last 800 ky show strong discrimination between loess and palaeosol units. Variations in susceptibility () and its frequency dependent part (FD) are consistent with a varying pedogenic component with fixed grain-size distri- bution superimposed on a background level (BG) of pristine loess material through- out the 62 m long profile. In the lower half a BG of 1.9*10-6 m3/kg was extrap- olated, opposed to 2.7*10-6 m3/kg in the upper half (with the exception of a 1 m interval at the base of a paleosol at 10 m depth). A variation in source material can be inferred. After subtraction of BG, FD is close to 14 % in paleosol and in loess layers, compliant with a log-normal grain-size distribution for the pedogenic magnetic fraction. Thermomagnetic measurements identify both magnetite and maghemite. The presence of superficially oxidised magnetite grains is inferred from measurements of rockmagnetic parameters before and after heating to 150 C. Hysteresis and back-field
measurements show minima for Hc and Hcr in paleosol layers. Viscous magnetisation in paleosol layers is an order of magnitude larger than in loess layers. Magnetic pa- rameters in the top half and the bottom half of the profile react in a different way to heating to 150 C. The magnitude of the changes after heating is proposed as a new analytical parameter. Measurements of hysteresis loops at several temperatures up to 500 C and at room temperature after these heating steps allow monitoring of temper- ature dependence of magnetic parameters and the detection of alterations involving magnetic minerals.- Publication:
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EGS General Assembly Conference Abstracts
- Pub Date:
- 2002
- Bibcode:
- 2002EGSGA..27.5859V