Post - Depositional Diagenesis and Chemical Remanent Magnetization - Paleomagnetism of Sedimentary Rocks: Process and Interpretation - page 80

of hematite, the NRM affects the direction of the CRM
acquired by the secondary magnetic minerals. The
resulting CRM is intermediate between the pre-existing
NRM direction and the magnetic fi eld direction during
growth, and is not an accurate representation of the
geomagnetic fi eld.
A remagnetization carried by a CRM can therefore
be accurate, but it depends on the magnetic environ-
ment in which the secondary magnetic minerals grew.
In the great Late Paleozoic remagnetization of eastern
North America caused by orogenically driven fl uid
fl ow, both the secondary magnetite in the carbonate

rocks and the secondary pigmentary hematite in the
clastic rocks probably grew from ' nothing ' i.e. there
were no permanently magnetic precursor minerals, so
the CRM acquired is an accurate record of the geomag-
netic fi eld. This is supported by paleopoles, carried by
the remagnetization, that are consistent with the
North American magnetic fi eld direction for the Late
Paleozoic. The accuracy of a remagnetization should
be considered on a case-by-case basis with the nature
of the precursor minerals an important point to inform
the interpretation of the secondary CRM.