Magnetic fabric analysis of the Plio-Pleistocene clayey units of the Sant’Arcangelo basin, southern Italy

This work represents the first attempt to use anisotropy of magnetic susceptibility (AMS) analysis for the characterization of the magnetic fabric of Plio-Pleistocene sediments in the southern Apennines of Italy. The area examined, the Sant’Arcangelo basin, has undergone mild deformation during the Pleistocene. Analysis was carried out on 182 cores sampled at 15 sites in unmetamorphosed, weakly deformed clays and marly clays. The data identify a magnetic fabric of clearly depositional—compactional origin even though a partial contribution of tectonic deformation to the AMS is also recognizable at many sites. The results presented here are compared with the existing structural and sedimentary data. In particular, a close consistency is found between the overall orientation of magnetic lineations and the compressional directions indicated by previous meso-structural analysis. We suggest that the magnetic fabric detected here arises from a limited overprint of strain effects related to compressional episodes on a primary, sedimentary, fabric. This interpretation allowed us to resolve the bedding attitude where the clayey units appear homogeneous in the field, and hence to suggest the appropriate bedding correction in concomitant paleomagnetic analysis, and to estimate the orientation and the relative
degree of deformation at each sampling site.