The Paleomagnetism of Sediments and Sedimentary Rocks: Importance and Reliability - Paleomagnetism of Sedimentary Rocks: Process and Interpretation - page 7

greater scatter in their recording of the Earth's fi eld,
probably because of the high water content of these
sediments and ease with which their DRM could be
disturbed by sampling. The inclinations of the subcores
differed by 3.1-8.5° with a median difference of 5.6°;
declinations differed by 3.6-15° with a median differ-
ence of 7.2 ° .
Another good example of the directional reproduc-
ibility of DRM records of paleosecular variation of the
geomagnetic fi eld comes from the data of Channell
et al . (2004) from Ocean Drilling Program (ODP) Site
983 in the North Atlantic. In this study the authors
report the Fisher mean and α 95 confi dence intervals for
the averaged DRMs from multiple u-channel sampling
of the core. The α 95 of inclination varies from as little
as 9° to as great as 31° with an average of 19°, while
the α 95 /cos I for declination varied from 18° to 38°
with a mean of 28° over the same interval in the core.
Since the 95% confi dence limit is twice the estimated
standard error of the mean, these confi dence limits for
Site 983 inclinations and declinations are equivalent
in magnitude to that observed for the Bermuda Rise
box core.
Quite a few paleosecular variation records have been
measured from both wet and dry lake sediments and
all show good repeatability of DRM records of the geo-

magnetic fi eld. The multiple records of the Mono Lake
geomagnetic excursion in the dry lake sediments of the
Wilson Creek Formation show good reproducibility,
even when the geomagnetic fi eld is moving very quickly
during the excursion (Liddicoat & Coe 1979). Before
and after the excursion, the four independent records
of the fi eld differ by up to about 10° in declination and
by 5-10° in inclination. During the excursion the
scatter increases somewhat; one inclination record
differs from the other three by 15-20° (Fig. 1.2).
More recent work on the stacked multiple paleosecu-
lar variation records from Lake El Trebol sediments in
Mexico show variations at a given horizon that are
about 8.5° for inclination and about 11° for declina-
tion (Irurzun et al . 2006 ). Creer & Tucholka (1982)
calculate standard errors around stacked PSV curves
from North American lakes and from lakes in the
British Isles. Their point is to show how repeatable the
DRM is in these wet lake sediments. For central North
American lakes, the standard error for declination is
typically 3° to as much as 23°, but averages about 8°.
The standard error in the inclination record is much
better, averaging only 2°. When the PSV records
from Lake Windermere are compared to those from
Loch Lomond the standard error is even less (about 2°
for declination and 1° for inclination). Stockhausen

DECLINATION INCLINATION

INTENSITY (×10 −5 )

300 330 0 30 −30 0 30 60 2 3 4 567891

10

CM

0

Fig. 1.2 Mono Lake geomagnetic excursion showing reproducibility of the geomagnetic fi eld direction by sedimentary rocks,
when the geomagnetic fi eld was moving fast. JC Liddicoat and RS Coe, Mono Lake geomagnetic excursion, Journal of
Geophysical Research , volume 84, 261-271, 1979. Copyright 1979 American Geophysical Union. Reproduced/modifi ed by
permission of American Geophysical Union.