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to have this ability, particularly if the sediment accu-
mulation rate is high. Fine-grained sediments can
more easily acquire an accurate post-depositional
remanence, but they are particularly susceptible to
compaction-caused inclination shallowing while
coarse sediments are not. It turns out that both coarse-
grained and fi ne - grained hematite - bearing sedimen-
tary rocks will likely have inclination shallowing, but
they will acquire the shallowing at different times
(either at or after deposition).
For completeness, two other early re-deposition
experiments conducted with hematite-bearing sedi-
ments should be mentioned. Lovlie and Torsvik (1984)
re-deposited naturally disaggregated Devonian Wood
Bay Formation red bed sediment collected from recent
fl oodplain deposits. They re-deposited the sediments in
fresh water over a period of 5-7 days, then allowed the
sediment to settle for an additional 4-6 days. What is
signifi cant about their study is that they conducted the
re-deposition in a range of fi eld inclinations and were
able to observe the tangent-tangent relationship ini-
tially proposed by King (1955). The inclinations of the
re-deposited red bed material had inclination shallow-
ing with
f
= 0.4, but there was a good deal of scatter in
their results. The other interesting observation from
their study is that deposition and settling over 1-2
weeks did not eliminate inclination shallowing. This is
consistent with experiments conducted with magnetite
in fresh water discussed in the previous section. Lovlie
& Torsvik (1984) also measured the anisotropy of
magnetic susceptibility (AMS) of the re-deposited sedi-
ments and saw a typical oblate depositional fabric with
vertical minimum principal axes and maximum prin-
cipal axes scattered in the horizontal. The earliest
hematite re-deposition experiment in the literature is
Bressler & Elston ' s (1980) re - deposition of sedimen-
tary material disaggregated from the Triassic Moenkopi
red beds. They observed inclination shallowing but not
the King (1955) tangent - tangent relationship between
remanent inclination and fi eld inclination.
Fig. 2.5
Illustration of early experimental work
investigating deposition on a sloping surface (15° in fi gure)
or from a water current. The Earth's fi eld inclination above
is set at 40°. The black solid arrows show an accurate DRM
in the sediment. The dashed arrows show the result of
rotation caused either by deposition on a sloping surface
(above) or from a current (below). The amount of rotation is
15° in the fi gure. Rotations are more complicated when the
water fl ow or slope is not in the magnetic meridian.
the observations and theory that resulted from these
early experiments.
The bedding error studied by these early workers
(notably King, Griffi ths and Rees) was for small dips
less than 10° and would be most applicable to the
foreset beds of water-laid cross-bedding. From the re-
deposition experiments a 'bedding error correction'
was developed in which the magnitude of the bedding
error was equal, or nearly equal, to the dip of the bed.
King (1955) and Griffi ths
et al
. (1960) looked at re-
depositions in which the dip of the bed was in the mag-
netic meridian and showed a change in inclination.
If the bed dipped in the direction of the magnetic fi eld,
the magnetic vector would steepen by approximately
the amount of dip, although some experiments showed
a grain-size dependence with the fi nest - grained sedi-
DEPOSITION ON A SLOPING BED AND
FROM A CURRENT
Early re-deposition experiments showed that initial
bedding slope and deposition from moving water could
affect the accuracy of a syn-depositional DRM (Fig.
2.5). Verosub (1977) provides a very useful review of
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