What question did this study set out to answer?

The aim is to investigate the tectonic evolution of the South Pyrenean Zone using anisotropy of magnetic susceptibility and paleomagnetic data.

April 5, 2026Studia Geophysica et Geodaetica0 citationsOpen Access

Magnetic fabrics and paleomagnetism of continental mudrocks: Implications for unravelling the tectonic evolution of the South Pyrenean Zone (NE Spain)

PSP. Sierra-CamposUniversidad de Zaragoza PCPablo Calvín EIEsther Izquierdo-LlavallUniversidad de Zaragoza

Key Points

The aim is to investigate the tectonic evolution of the South Pyrenean Zone using anisotropy of magnetic susceptibility and paleomagnetic data.
Conducted a combined anisotropy of magnetic susceptibility (AMS) and paleomagnetic analysis along a stratigraphic section of the Campodarbe Formation.
Analyzed magnetic fabrics and vertical axis rotations across different stratigraphic levels.
Interpreted magnetic data for understanding layer parallel shortening related to basement thrust activity.
Identified dominant oblate ellipsoids and WNW-ESE horizontal magnetic lineations in the magnetic fabrics.
Observed clockwise vertical axis rotations of 6º to 12º in the lower section, and counterclockwise rotations of 7º to 14º in the upper section.
Determined a total net rotation of approximately 25º between the lower and upper parts of the stratigraphic section.

Abstract

Abstract The anisotropy of the magnetic susceptibility (AMS) in mudrocks has been widely used to study orogenic belts due to their sensitivity to strain, while paleomagnetism remains the most effective method to quantify vertical axis rotations (VARs) resulting from the accommodation of along-strike variations in shortening. However, AMS can be also eventually used as a passive marker to detect VARs and the integration of both techniques offers a powerful approach to understand the tectonic evolution of fold-and-thrusts-belts. In this work, a combined AMS and paleomagnetic study along a stratigraphic section of continental rocks from the Campodarbe Formation in the Jaca-Pamplona Basin, southern Pyrenees, was carried out. This stratigraphic section (Martes section) records the tectonic evolution of this part of the basin from Priabonian to Rupelian times. The magnetic fabrics show the imprint of early stages of deformation, characterized by dominantly oblate ellipsoids and WNW-ESE horizontal magnetic lineations (axes of maximum magnetic susceptibility k max ), parallel to bedding and the main regional structures. In the lower part of the section, k max axes trend around 290º, gradually rotating to 270º towards the top. The AMS is interpreted as locked under the imprint of the layer parallel shortening (LPS) associated to the activity of the basement thrusts in the northern Jaca-Pamplona Basin. On the other hand, paleomagnetic data indicate clockwise VARs of 6º to 12º in the lower part of the section, and a counterclockwise rotation of 7º to 14º in the upper part. These differential rotations could result from lateral changes in the Biniés basement thrust or the Jaca thrust system that were active during Oligocene times. Both techniques record a net rotation of ca. 25º between the lower and upper part of the section, which support the interpretation that early-locked AMS behaves as a passive marker and validates its use for detecting and quantifying VARs.

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