Paleomagnetic study of the curvature of the Segre oblique zone (Southern Pyrenees).

The origin of the obliquity of the structures at the eastern end of the central South-Pyrenean salient is investigated by means of Paleomagnetism. Earlier paleomagnetic data in the area are poorly distributed and insufficient to describe in detail the amount and age of vertical axis-rotations affecting the region. This work aims to address this issue by focusing on the Palaeocene rocks, whose magnetization if primary would record the entire rotation during the emplacement of the thrust sheet units, improving our understanding of the history of deformation and the paleogeographic implications during the Eocene. In addition to Palaeocene Garumnian facies, late Cretaceous and early Eocene marine facies were also sampled. The characteristic components of the magnetization were obtained after progressive demagnetization of the NRM of a minimum of 10 samples per site. The mean site direction, and the mean direction of groups of sites from the same structural unit were calculated. The fold test applied to a set of sites located on the Montsec thrust sheet gave positive results, indicating an age of the magnetization prior to deformation. However, evidence of postfolding magnetizations were found in other sites. The results of this study indicate significant counterclockwise rotations of the Cadí, Port del Comte, and the eastern termination of the Montsec thrust sheets, developed during the Mid Eocene to Oligocene times. These results are intended to contribute to the restitution of the initial geometry of the structures and to contribute to the paleogeographic reconstruction of the sedimentary systems of the eastern and central Pyrenees.