Lithology-dependent reliability of AMS analysis: A case study of the Eocene turbidities in the southern Pyrenees (Aragَn, Spain)

Fine-grained sediments are generally better strain-markers in the outer part of orogenic belts and foreland basins because they are more prone to cleavage formation than coarse detrital rocks in diagenetic to very-low metamorphic environments. This also commonly applies to magnetic fabric analysis, thus favoring sampling in fine-grained rocks. In this article, this general assumption is tested sampling for anisotropy of magnetic susceptibility (AMS) analysis along different levels of Bouma sequences in turbidites from the Eocene South-Pyrenean turbiditic basin, above and below the cleavage front. Application of other techniques (LTAMS, AGRM and hard-APARM) indicates that the cleavage imprint in AMS fabrics is carried by paramagnetic particles, in this case, by clay minerals. The results obtained show that: (i) directional results of AMS are similar in the different levels of the Bouma sequence; (ii) the paramagnetic contribution to the susceptibility is independent from the lithology; and (iii) the equivalent paramagnetic contribution to susceptibility (detrital sedimentary particles) does not show differences between a to d (sandstones) and e-level (siltstones and shales).