Inclination Shallowing in Sedimentary Rocks: Evidence, Mechanism and Cause - Paleomagnetism of Sedimentary Rocks: Process and Interpretation - page 45

volcanic rocks (Hankard et al . 2007 ; Dupont - Nivet et
al . 2010) implicated inclination shallowing for sedi-
mentary results from central Asia. In all these studies,
the authors recognized that inclination shallowing
had affected their results. Some of the later studies
applied the EI correction to their results (Wang & Yang
2007 ; Tan et al . 2010 ). The average fl attening factor of
f = 0.51 for these six studies suggests inclination shal-
lowing of about 25° for these rocks and paleolatitude
anomalies of about 15°.
Inclination shallowing in red beds has been observed
in other places outside of China. Taylor et al . (2009)
observed shallowing in Permo-Triassic red beds from
the Urals in Russia. Based on far-sided paleomagnetic
poles for their data, they suggest inclination shallow-
ing has affected their results. Iosifi di et al . (2010)
detected it in Permo-Carboniferous red and gray sedi-
mentary rocks in the Ukraine. In their results the
component isolated at the highest demagnetization
temperatures was shallower by 12° than the compo-
nent removed at intermediate temperatures. The
assumption they made is that the high-temperature
component was carried by detrital hematite and
affected by shallowing, while the intermediate tem-
perature component was carried by a CRM in pigmen-
tary hematite and unaffected by shallowing. This
would predict a very low f factor for these rocks, so the
f factor in Table 4.2 is derived from comparison of Iosi-
fi di et al .'s results to the directions predicted from the
accepted apparent polar wander path for this part of
the world (Torsvik et al . 2008 ). Finally, Rapalini (2006)
used AMS and IRM analysis to detect shallowing in
Neoprotereozic (Ediacaran) red claystones from the
Sierra de los Barrientos in Argentina.
Bilardello

inclination-shallowing corrections had been con-
ducted. From a separate set of studies ( N = 15), they
found an average f factor of 0.59 which agreed nicely
with the average f factor of 0.51 calculated for the 11
studies discussed here and listed in Table 4.2. Hematite-
bearing rocks appear to be more affected by shallowing
than magnetite-bearing rocks with shallowing of
25 - 30 ° for intermediate initial inclinations. This
could be due to the combination of demonstrated syn-
depositional shallowing (e.g. Tauxe & Kent 1984; Tan
et al . 2002 ) and compaction - induced shallowing for
fi ner - grained facies.
For completeness, we should point out that there are
several studies of sedimentary rocks that explicitly
looked for inclination shallowing and did not observe
any. Smethurst & McEnroe (2003) compared Silurian
volcanic and red bed directions from Newfoundland
and saw no difference, although earlier studies (Stama-
takos et al . 1994) did see evidence of shallowing. Rapa-
lini et al . (2006) applied an IRM at 45° (the Hodych &
Buchan 1994 correction technique) to Permian red
beds from South America and saw no evidence of shal-
lowing. Sun et al . (2006) compared directions from
Cretaceous red beds and basalts from the Qaidam Block
in China and saw no evidence of inclination shallow-
ing in the red beds. Finally, Schmidt et al . (2009) per-
formed a detailed IRM analysis of the Nucaleena
Formation cap carbonate rocks from Australia and
found no evidence of shallowing. What these studies
show is that while inclination shallowing is much
more common in rocks than originally thought, it is
not present in absolutely every sedimentary rock. In
the next chapter we will examine in detail techniques
to identify and correct for inclination shallowing in
sedimentary rocks. & Kodama (2010b) also summarized

the f factors for hematite-bearing rocks for which