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experiments. The experiments by Barton & McElhinny
(1979) and Levi & Banerjee (1990) were conducted
with lake sediment that was described as organic-rich
mud or as silty mud that had about 10% organics and
50% clay content (Lake St Croix sediments). It is highly
likely that organic fl occules were present in these re-
deposition experiments while clay fl occules are less
likely to have been present because fresh water was
most likely used.
Only the Mitra & Tauxe (2009) experiments studied
inclination error and varied the salinity of the water.
The synthetic sediments were composed of clay and
maghemite, and settled over 2 weeks. The lowest salin-
ity results reported (about 2 ppt) showed inclination
shallowing with an f factor of about 0.5 (fi eld inclina-
tion c. 45°, measured inclination c. 27°). Levi and Ban-
erjee's slower experiments, which showed small
inclination errors ( f = 0.93), were conducted over
' several ' weeks. Barton and McElhinny ' s experiment,
conducted over 9 months, showed no inclination error.
The initial explanation for the shallow inclinations in
the King and Griffi ths et al . experiments, that the re-
deposition occurred too quickly for the particles to
become aligned, is probably correct. From the experi-
mental data in the literature, for freshwater laboratory
deposition the longer the deposition time the smaller
the inclination error. This interpretation can also
explain results for sediments that are likely to contain
organic fl occules.
Soan River ( f = 0.4). The declination of the re - deposited
sediment remained accurate. The laboratory re-
deposition was conducted in fresh water to minimize
fl occulation and, of course, the Soan River re-deposition
also occurred in fresh water. Furthermore, both re-
deposition experiments occurred in a short time, the
Soan River sediments were deposited 'during the rains
two weeks prior to sampling' and the laboratory re-
deposited sediment was allowed to settle overnight (or
until the settling tubes became clear) i.e. about 5
hours. These results support the interpretation that the
syn-depositional inclination error is due to rapid depo-
sition, and it may be eradicated by very slow deposition
or by realignment of magnetic particles during the
acquisition of a post-depositional remanence. Further-
more, Tauxe and Kent showed that their re-deposited
sediments could acquire a pDRM and that it accurately
recorded the fi eld.
Tan et al . (2002) conducted laboratory re - deposition
experiments with material obtained by breaking down
Eocene Suweiyi Formation red beds from central Asia.
They ultra-sonicated the red beds to liberate the mag-
netic mineral (hematite) from the non-magnetic matrix
grains, added the material to distilled water to make a
slurry and let the slurry settle in a laboratory magnetic
fi eld with an inclination of 58°. Unexpectedly, the
slurry spontaneously segregated into two different
grain size fractions: fi ne and coarse. The fi ne - grained
slurry, whose paleomagnetism is apparently carried by
pigmentary hematite grains, acquired an accurate
record of the laboratory fi eld direction after several
hours of settling, and was then compacted with
volume losses up to 70%. Their inclination was subse-
quently shallowed by compaction ( f = 0.52). In the
re-deposition experiments with the coarse-grained
fraction, signifi cant syn-depositional shallowing was
observed that ranged from as much as f = 0.34 but as
little as f = 0.96. For two of the eight coarse-grained
sediment re-deposition experiments, inclinations actu-
ally steepened ( f = 1.10 and f = 1.38).
One critical observation from this work is that the
faster the deposition rate, the shallower the inclination
at deposition. Signifi cantly, coarse - grained sediments
lost little inclination when compacted, probably
because volume losses of only 10% could be obtained
at the same pressures that caused 70% volume loss in
the fi ne - grained sediments. Tan et al . (2002) conclude
that the occurrence of an inclination error depends
on the ability of hematite grains to reorient post-
depositionally. Coarse-grained sediments are less likely
LABORATORY RE-DEPOSITION
EXPERIMENTS FOR HEMATITE-
BEARING SEDIMENTS
There have only been a few laboratory re-deposition
studies using hematite-bearing sedimentary rocks, i.e.
red beds, probably because the overwhelming bias
among paleomagnetists is that red beds carry a sec-
ondary CRM rather than a DRM. However, the evi-
dence from the anisotropy results for red beds indicate
that the possibility of a red bed DRM should be taken
seriously. Tauxe & Kent (1984) conducted a pioneering
set of re-deposition experiments. They investigated the
natural re-deposition of Siwalik Formation red bed
sediment after fl ood events along the Soan River in
Pakistan and also laboratory re-deposition of the same
material. Tauxe and Kent observed signifi cant inclina-
tion shallowing in the laboratory ( f = 0.55) and in the
natural re-deposition of Siwalik material along the
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