The magnetic fabric of undisturbed and redeposited loess measured by anisotropy of magnetic susceptibility (AMS)

Abstract

101 samples originating from different sites were measured by KLY-1 Kappabridge (Geofyzika, Brno).
The dull yellow, carbonate-cemented, well-compacted, homogenous (i.e. not layered) samples (55 pieces)
of typical loess were collected from Basaharc, Galgahévíz, Hévízgyörk, Isaszeg and Sióagárd. Root cells,
fine-grained sand, sandy loess biogallery infill (bioturbation), Hmonite and manganese concretion
(indicating the hydromorph effect or the pedogenesis) were identified in the reworked loess samples (7
pieces) which originated from Dunaszekcső. The typical and well bioturbated loess was collected from
loess above Bag tephra. Fine-bedded loess was collected from Vácbottyán and Verőce (25 pieces),
pedosediment samples from the bed of Hévízgyörk site (10 pieces) and palaeovalley infill from the Bag
outcrop (4 pieces) and defined as redeposited loess.
The magnetic mineral of the pilot samples was determined by isothermal remanent magnetisation
(IRM) measurements. The samples were magnetized in fields from 200 mT to 10 000 m l The normalized
IRM curves (IRM/IRMmax ) showed significant similarities in all of the samples. There were no differences
between the redeposited, well-bioturbated and wind blown loess. The dominant phase was the
magnetite/maghemite in the magnetic fabric that determinate the magnetic character of samples based
on the analysis of the IRM. 3000 /IRM m a x ratio (0.84-0.89).
The principal susceptibilities (к тах , к^,, K min ) and the foliation (F), lineation (L), degree of anisotropy
(P) and ellipsoid shape factor (E) were calculated. The AMS index numbers were elaborated by statistical
analysis and by the presentation of principal susceptibilities in the geographical coordinate system on a
stereographical projection (GeoOrient free software).
Three methods were applied to distinguish the undisturbed, redeposited and bioturbated loesses. The
wind blown, bioturbated and the redeposited loesses were separated clearly by the P values of the
samples, the histogram analysis of foliation and lineation, F and L plotting on a diagram, and on the
stereographical projection.
A group with a new magnetic fabric character within the "redeposited loess group" was identified.
The macroscopically laminated loess samples had the highest average P value (1.024-1.074) and the