La mesure de l'anisotropie de susceptibilité magnétique dans les flyschs: Application à la recherche des directions des paléocourants

Studies made on the anisotropy of magnetic susceptibility of artificial sediments have shown that there are correlations between the orientation of anisotropy axes and of transport directions. Thus, the analysis of parameters of anisotropy of magnetic susceptibility can constitute a means to investigate transport directions in flysch. To test this method in a natural model, the authors have made some measurements on flysch beds belonging to the “grés d'Annot complex”. The sediments have been sampled in the Contes and Peira-Cava synclines where the directions of paleocurrents have been determinated by classical methods. Results obtained both in Contes and in Peira-Cava on fine-grained detrital beds show a good agreement between directions of paleo-transport deduced from orientation of anisotropy axes and those established by classical methods on the levels showing “sole-marks”. However, in some beds of the Peira-Cava syncline, which are characterized by coarser grain size and “sole-marks” of good quality, the scattering of the directions of the anisotropy axes is very great and in some cases the measurements are not reproducible in the same sample.It appears, therefore, that the measurement of the anisotropy of magnetic susceptibility can constitute a good approach to analysing emplacement modes of fine-grained flysch deposits in which the use of classical methods is often difficult. This method of paleocurrent analysis complements the other techniques used in this field of research.