The recognition of pervasive remagnetization
of the natural remanent magnetization (NRM) is essential for a correct
interpretation of paleomagnetic data and has, for instance, important geodynamical
implications. It has only recently become apparent that this ‘remagnetization
syndrome’ may be much more widespread than previously thought, particularly
in sedimentary rocks of forelands and outer margins of orogenic zones.
These rocks are often considered to deliver ‘ideal’ high-quality paleomagnetic
data, an assumption that needs serious reconsideration.
The research aimed to address the mechanisms
that are responsible for remagnetization by comparing remagnetized and
non-remagnetized areas. The target is to develop the simplest possible
criteria that are diagnostic of remagnetization that are independent of
paleomagnetic directional data. The research strategy involves optimizing
a blend of mineral-magnetic, paleomagnetic and non-magnetic methods. The
latter methods include classical thin section analysis, SEM/TEM microscopy
on magnetic concentrates, determination of smectite/illite ratios, as well
as determination of the trace element and 87Sr/86Sr
ratios in carbonates to detect modifications by basinal orogenic fluids.
Fieldwork was planned in Paleozoic rocks
in the Ardennes (remagnetized) and in Brittany (claimed to be non- remagnetized).
A transect comprising remagnetized and non-remagnetized marly rocks of
Cretaceous age in the Pyrenees will serve as a testcase for the criteria
to be developed.