Magnetic fabric in “undeformed” marine clays from compressional zones

We present the results of magnetic fabric analysis obtained on samples of marine clays from sedimentary sequences in Northwestern Greece and Taiwan, in regions which have been submitted to large scale compressional events. The lithology of the sediments is mainly composed of unmetamorphosed marls, siltstones and sandstones. These formations are folded and faulted at different scales. The magnetic fabric is largely sedimentary. However both at single sites (Taiwan) and regionally (Greece) the magnetic lineation is systematically perpendicular to the main compressive stress σ1 inferred from previous fault tectonic analysis. This is an indication that the fabric is also partly of tectonic origin. In Northwestern Greece the orientation of the magnetic susceptibility ellipsoid is constant over distances exceeding 200 km, suggesting that the orientation of the principal compressive strain relative to the trend of the main structures lias been constant since Lower Oligocene.