The rotation of Iberia during the Aptian and consequences for pervasive Cretaceous remagnetization. Geologica Ultraiectina (292)

Abstract

To answer when, how, and where Iberia rotated as well as when and why the Iberian remagnetization happened in the Cretaceous, this Ph.D project was carried out in the Organyà Basin, southern Pyrenees, northern Spain. The research described in this thesis can be categorized into two main topics: 1) the Cretaceous rotation of Iberia and the related palinspastic reconstruction, and 2) the implications for the recording of the natural remanent magnetization (NRM), notably the extent to which the rocks are remagnetized (this is they contain an NRM signal that is younger than the age of the rock unit it is retrieved from). Our results show that the entire Iberian rotation of ~35 counterclockwise with respect to Eurasia occurred during the Aptian. The rotation is faster in the early Aptian and seems to slow down during the middle and late Aptian. The anisotropy of the magnetic susceptibility (AMS) analysis implies a position of the Organyà Basin westerly of the Iberian rotation pivot point during its rotation. In this frame, the palinspastic position of Iberia during its rotation and eastward movement to its position before the onset of the Pyrenean orogeny is discussed. Remagnetization is first studied in the Organyà Basin and then combined with the record in several other Mesozoic Iberian basins to provide constraints on its timing. The proposed mechanism for the Cretaceous Iberian remagnetization is likely a basin-confined event during the rifting phase. Finally a new approach to recognize remagnetization independent of paleomagnetic directional analysis is proposed.