| dc.description.abstract | Paleosecular magnetic changes through a 1.5m section of post-glacial lacustrine deposits
are strongly influenced by mineralogy and differential compaction. The sediments chiefly
comprise clay and, in the lower one third part of the section, rhythmites which vary from ~2mm
to ~Scm in thickness. 125 paleomagnetic specimens were collected in total from the 1.5m section.
Anisotropy of magnetic susceptibility and anisotropy of anhysteretic remanent magnetization
identify a magnetic fabric with maximum susceptibility parallel to the bedding plane of the
sediments and with a preferred northwest-southeast axis, probably indicating paleo-current
alignment. Minimum susceptibility represents the pole to bedding, due to grain alignment.
Incremental acquisition and demagnetization of isothermal and anhysteretic
magnetizations and the orthogonal three-axis test indicate that the sediments contain two
magnetic phases with different coercivities. Magnetic hysteresis measurements (clays n=226; silts
n=37) show that clay is dominated by single domain magnetite and hematite (means of
M5=58.47±9.22Am2
, Mrs=17.12±27.22Am2
, Hc=21.09±7.69mT, Hcr=62.04±4.09mT) whereas silt
is dominated by pseudo-single domain and single domain magnetite (means of
M5=681.0±395.9Am2
, Mrs=163.2±84.75Am2
, Hc=26.07±2.94mT, Hcr=56.08±3.17mT). The silt is
dominated by magnetite, whereas the clay carries both hematite and magnetite. | en_US |
