How to Detect and Correct a Compaction - shallowed Inclination - Paleomagnetism of Sedimentary Rocks: Process and Interpretation - page 55

K min and K max are the minimum and maximum princi-
pal anisotropies for the remanent anisotropy used for
the inclination correction of hematite-bearing rocks,
i.e. the maximum and minimum axes of the anisotropy
ellipsoid. The remanence anisotropy is a bit trickier to
measure for hematite-bearing rocks because hematite
has such a high coercivity. ARM will not work because
most laboratories do not have equipment that can
apply an ARM to hematite-bearing rocks. We will see
that different approaches have been used to measure
the anisotropy of the hematite grains carrying the
demagnetized remanence of red sedimentary rocks.
It is worth noting that the all-important individual
particle remanence anisotropy can vary widely for
magnetite because it is controlled by shape; for hema-
tite however, since the individual particle anisotropy is
controlled by crystallography, it tends to be fairly con-
strained in magnitude. This is a benefi t to inclination-
shallowing corrections for hematite-bearing rocks
since a fairly good correction can result from using a
value close to 1.4-1.45 and the diffi cult procedures for
measuring the hematite individual particle anisotropy
can be avoided (Kodama 2009).

Fig. 5.8 Red dots show paleopoles based on red beds for
the Mesozoic and Paleozoic. Open squares show Van der
Voo's (1990) mean paleopoles for the lower Tertiary (Tl),
upper Cretaceous (Ku), upper Jurassic (Ju), lower Jurassic
(Jl), upper Triassic (Tru), lower Triassic (Trl), upper Permian
(Pu), lower Permian (Pl), upper Carboniferous (Cu), lower
Carboniferous (Cl), upper Devonian (Du), lower Devonian
(Dl), upper Silurian/lower Devonian (Su/Dl) and middle
Ordovician (Om). The more modern APWP of Besse &
Courtillot (2002) only extends back to 200 Ma, or between
the Tru and Jl mean paleopoles. North America's APWP for
earlier times relies heavily on results from red beds.
(See Colour Plate 7)

RED BED INCLINATION SHALLOWING

Making inclination corrections to magnetite-bearing
marine sedimentary rocks is fairly non-controversial if
the distinct possibility of inclination shallowing is
accepted; because magnetite is recognized as a primary
magnetic mineral in sedimentary rocks, it could be
affected by post-depositional compaction. Inclination
corrections of red sedimentary rocks, i.e. red beds, are
controversial simply because there's no consensus
within the paleomagnetic community about whether
the paleomagnetism of red beds is a primary deposi-
tional remanence or a secondary chemical remanent
magnetization acquired when magnetic minerals are
formed post-depositionally. This controversy has been
denoted the 'red bed controversy' (see Butler 1992 for
more details). Despite the lack of a clear consensus
about the magnetization mechanism of red beds, there
is one simple reason to pursue an inclination correc-
tion for red beds. They have a strong, stable paleomag-
netism, are abundant in the geologic record and are a
common target of paleomagnetic studies. Further-
more, anisotropy measurements made for inclination
corrections can shed some important light on the
timing and manner of red bed magnetization acquisi-

tion and help answer the question about whether the
red bed remanence is primary.
The importance of red bed paleomagnetic data is
demonstrated by the dominance of red bed paleomag-
netic poles in North America ' s Mid - Paleozoic - Early
Mesozoic apparent polar wander path (APWP). When
the mean North American paleopoles are compared to
the red bed paleopoles (Fig. 5.8), it is apparent that the
position of the mean paleopoles is controlled to large
extent by the red bed data from the Upper Devonian-
Lower Jurassic.
The importance of red beds for determining a conti-
nent's ancient APWP is particularly acute because the
preferred APWPs, those constructed synthetically for
each continent from an averaging of the global paleo-
magnetic pole database (Besse & Courtillot 2002), only