Diachronous pervasive remagnetization in northern Iberian basins during Cretaceous rotation and extension

Abstract

Northern Iberia exposes a series of Mesozoic sedimentary basins, whose final formation history is tied to a rotation episode of Iberia during the Aptian, related to the opening of the Bay of Biscay. Many of these basins experienced widespread remagnetization, previously loosely tied to a ‘Mid-Cretaceous thermal event’. Here we make use of the improved apparent polar wander path (APWP) of Iberia to narrowly constrain the age of their remagnetization to show that several basins experienced a regional diachronous remagnetization. We apply the small circle intersection (SCI) method to reconstruct the paleomagnetic field direction during remagnetization in the Organyà Basin in the Southern Pyrenees, Spain, where the age of remagnetization is stratigraphically well-dated to around the Barremian–Aptian boundary, and where the paleomagnetic direction during remagnetization has been well-established. The resulting direction of D/ I = 316.8 ± 5.7°/54.8° ± 3.3° (where the uncertainty in declination is approximated by α 95 / cos I and the error in inclination by α 95) corresponds closely to a recently improved APWP of Iberia, providing support for the applicability of this method. Application of the SCI method allows us to show that the older portion of the remagnetized beds was already tilted by ~ 15–20° to the South during the remagnetization as a result of half-graben formation in the Organyà Basin. Moreover, the positive outcome of the SCI technique enables us to argue that previously published results from three other basins—the Cabuérniga and Cameros Basins and the Iberian Range—can be straightforwardly compared to the APWP. Hence, we show that the four pervasively remagnetized basins under consideration all acquired their remagnetization at different times. The remagnetization events were thus confined to these sedimentary basins on an individual ‘per basin’ scale—albeit occurring on a regional scale over a period of at least ~ 10–15 Myr. Therefore, we propose that the Cretaceous remagnetization events in northern Iberia are related to the extensional tectonic rifting. The pervasive remagnetization is most likely basin confined because there is no apparent overall regional or temporal trend among the basins. Reasonable explanations for remagnetization are those that can occur on the scale and within the context of individual sedimentary basins. These include the interplay of burial depth and an elevated geothermal gradient to reach the diagenetic temperatures required for magnetite-producing reactions. In the Iberian situation, there is no need to invoke more speculative regional Iberia-wide mechanisms.