Sy. Hu et al., Environmental mechanism of magnetic susceptibility changes of lacustrine sediments from Lake Hulun, China, SCI CHINA D, 43(5), 2000, pp. 534-540
The changes of magnetic susceptibility (kappa) are correlated with those of
corresponding sedimentological, geochemical, mineralogical and biological
results, which verifies that kappa can be taken as one of the environmental
proxies. However, usually the exact origin of magnetic signal is poorly un
derstood, and is difficult to relate with the environmental evolution. Magn
etic properties of material derived from the catchment and sedimentary envi
ronment may affect the accumulation, preservation, or authigenesis and diag
enesis of magnetic minerals. In the Lake Hulun region in inner Mongolia, it
is found that muddy sediments, deposited during high water level period (c
orresponding to humid climate), have comparatively high kappa values. In co
ntrast, the sandy sediments, deposited during low water level period (corre
sponding to arid climate), have low kappa values. Detailed rock magnetic in
vestigation confirms that detrital magnetite derived from volcanic rocks in
the catchment exists in both muddy and sandy sediments. During high water
level period, secondary ferrimagnetic iron sulphide was produced in muddy s
ediments under relatively reductive conditions. Ferrimagnetic iron sulphide
, coexisting with detrital magnetite, predominates the magnetic properties
of muddy sediments, resulting in increasing kappa: This paper reveals the s
ignificance of authigenic ferrimagnetic iron sulphide produced after sedime
nt deposition.