The recognition of pervasive remagnetization of the natural remanent magnetization (NRM) is essential for a correct interpretation of paleomagnetic data and, evidently, has important geodynamical implications.  It has only recently become apparent that this ‘remagnetization syndrome’ may be much more widespread than previously anticipated, particularly in sedimentary rocks of forelands and outer margins of orogenic zones.  The proposed research revolves around the Organya basin of Cretaceous age in the Pyrenees  Limestones and marly limestones constitute most of the lithology.  The NRM of the rocks is argued to be non-remagnetized in the top while it is remagnetized in the bottom (Dinarès-Turell, J. and Garcia-Senz, J., 2000).

Orienting cores in Bajocian limestones in Aguilon

The Font Bordonera marls below the Santa Fe formation, Organya Basin

Sampling the Font Bordonera marls on the northern side of the Organya syncline

The remagnetization could be the consequence of  externally derived basinal fluids or the result of burial diagenesis with a much more limited involvement of external fluids. 

Santa Fe formation, Organya Basin

Sampling the Santa Fe formation, Organya Basin

To answer this question, the research strategy involves optimizing a blend of mineral-magnetic, paleomagnetic and ‘non-magnetic’ methods. The latter methods include thin section and SEM/TEM microscopy on rocks and magnetic concentrates, determination of the ⁸⁷Sr/⁸⁶Sr ratio from carbonates, and the determination of smectite/illite ratios. The target is to extend the criteria to diagnose remagnetization and to provide a more reliable basis for existing criteria, independent of the analysis of paleomagnetic directions.

The research has also been extended to Jurassic limestones from the Aguilon basin which show a pervasive Cretaceous overprint and hence a partial remagnetization. Yet, part of the original (Jurassic) signal has been preserved.

Kimmeridgian and Tithonian limestones near Aguilon

Springtime (above) and sampling (below) in the Aguilon Basin

• Gong, Z., Dekkers, M.J., Heslop, D. and Mullender, T.A.T. (2009). End-member modelling of isothermal magnetization (IRM) acquisition curves: A novel approach to diagnose remagnetization, Geophy. J. Int., 178, 693-701. 
• Gong, Z., Van Hinsbergen, D.J.J., Vissers, R.L.M. and Dekkers, M.J. (2009). Early Cretaceous syn-rotational extension in the Organyà basin: new constraints on the palinspastic position of Iberia during its rotation, Tectonophysics, 473, 312-323. 
• Gong, Z., Van Hinsbergen, D.J.J., Dekkers, M.J. (2009). Diachronous pervasive remagnetization in northern Iberian basins during Cretaceous rotation and extension, Earth Planet. Sci. Lett., 284, 292-301 

• Gong, Z., Dekkers, M.J., Dinarès-Turell, J. and Mullender, T.A.T. (2008). Remagnetization mechanism of Lower Cretaceous rocks from the Organyà Basin (Pyrenees, Spain), Studia Geoph. Geod., 52, 187-210. 
• Gong, Z., Langereis, C.G. and Mullender, T.A.T. (2008). The rotation of Iberia during the Aptian and the opening of the Bay of Biscay, Earth Planet. Sci. Lett., 273, 80-93 
• Gong, Z. (2008). The rotation of Iberia during the Aptian and consequences for pervasive Cretaceous remagnetization (PhD Thesis Utrecht University), Geologica Ultraiectina, 292, 103 pp.