DIFFERENT STYLES OF REMAGNETIZATION IN DEVONIAN SEDIMENTS FROM THE NORTH-WESTERN SAHARA (ALGERIA)

Sediments of Devonian age located in three areas of North Africa have been affected to different degrees by the Hercynian Orogeny. They show various remagnetizations of Carboniferous, Permian and Pleistocene ag e. In the Ben-Zireg anticline near the Variscan front in Algeria, the main phase of magnetic overprinting occurs during the Tournaisian. It is superimposed on a Famennian primary direction carried by magnetite. In the Beni-Abbes area to the South of the Variscan belt, griotte lim estones of Famennian age show a strong recent remagnetization with few residual Permian directions. This overprinting shows a shallower incl ination than the present-day field, with a small westward declination. Remagnetization is associated to magnetic transformation of sulphides . The transition of sulphides into magnetite-type minerals, as reveale d in the thermomagnetic curves from rocks of the Variscan Belt, preser ved the carrier against future magnetic overprinting. Compared to part ially remagnetized rocks, this mechanism is referable to recrystalliza tion during deformation.