Inclination Shallowing in Sedimentary Rocks: Evidence, Mechanism and Cause - Paleomagnetism of Sedimentary Rocks: Process and Interpretation - page 39

Fig. 4.4 SEM picture from Sun & Kodama (1992) showing
acicular magnetite particles (circled) sticking to clay grains
in high - porosity clay - rich sediment. W - W Sun and KP
Kodama, Magnetic anisotropy, scanning electron
microscopy, and x ray pole fi gure goniometry study of
inclination shallowing in a compacting clay-rich sediment,
Journal of Geophysical Research , 97, 19599 - 19615, 1992.
Copyright 1992 American Geophysical Union. Reproduced
by kind permission of American Geophysical Union.

domains are similar to the fl ocs envisioned by Katari et
al . (2000) to control the DRM acquisition of clay- and
organic-rich sediments. Magnetic anisotropy and x-ray
pole fi gure goniometry was also measured in Sun &
Kodama's (1992) experiments, showing that both of
these parameters also followed this two-part change
during compaction. Sun and Kodama's model for incli-
nation shallowing included a clay-magnetite sticking
mechanism but also saw that incorporation into the
clay fabric and the development of the clay fabric were
important factors in shallowing, thus showing how the
clay content of a sediment was critical for causing fl at-
tening (Fig. 4.5 ).
The natural sediments in Sun and Kodama's experi-
ments had 50% clay content. Subsequent work by Tan
& Kodama (1998) showed how the magnitude of incli-
nation shallowing was directly related to the clay
content of a sediment (Fig. 4.6).
One fi nal point should be noted from the Sun &
Kodama (1992) studies. Sun and Kodama argue that
the porosities of their laboratory-compacted sediments
suggest that inclination fl attening occurs at burial
depths of several hundred meters in the sediment
column in marine sediments. The void ratios of their
sediments indicate that their starting porosities are c.

Fig. 4.5 Microscopic model for inclination shallowing from
Sun & Kodama (1992) in which magnetite grains stick to
clay grains in high-porosity sediments and are then
incorporated into developing clay domains. The clay fabric is
then rotated into the horizontal after the break in slope of
the inclination shallowing versus pressure compaction
curves. W-W Sun and KP Kodama, Magnetic anisotropy,
scanning electron microscopy, and x ray pole fi gure
goniometry study of inclination shallowing in a compacting
clay - rich sediment, Journal of Geophysical Research , 97,
19599-19615, 1992. Copyright 1992 American
Geophysical Union. Reproduced by kind permission of
American Geophysical Union.

80-85% for the kaolinite and natural marine sedi-
ments, consistent with initial porosities of sediments
collected by the Ocean Drilling Project (ODP). By pres-
sures of 0.02 MPa in Sun and Kodama's experiments,
essentially when the rate of volume loss and inclination-
shallowing changes and the fl at - lying clay fabric is
fi rst established, the porosity of the sediment is 67-
76%. When compared to ODP results from similar
composition sediments, this indicates a depth of burial
of c. 200 m.