Imprint of paleocurrents, extensional and compressional deformation in the magnetic fabrics of the Permo-Triassic red beds of the Cadí Basin (Eastern Pyrenees)

Abstract

AbstractA magnetic fabric study was carried out in Permo-Triassic continental sedimentary red beds from the Cadí Basin (Eastern Pyrenees). These rocks were deposited on the top of a volcanic sequence when the regional tectonic regime changed from transtension to extension. Standard paleomagnetic cores (cylinders), cubes and irregular fragments were obtained for this study in 25 sites distributed throughout the basin. The “fragment methodology”, using oriented irregular fragments in claystones, is demonstrated to be successful and replicable. The aims of this study are (i) to interpret the magnetic fabrics in red beds according to sedimentary or tectonic models; (ii) to establish the relationship between the magnetic fabrics in the sedimentary red beds and the magnetic fabrics previously obtained in the underlying volcanic series, and (iii) to compare magnetic fabrics in continental sediments with other basins of the same age to interpret the tectonic scenario in the Iberian plate during Permian and Triassic times. The results obtained reveal a primary magnetic fabric that recorded a syn-sedimentary stretching in two nearly perpendicular directions, WNW-ESE and N-S, linked to basin development. Other sedimentary and tectonic factors, such as paleocurrents and deformation derived from the Alpine compression did not have a significant influence on the development of magnetic fabrics. The geodynamic scenario of the Iberian plate during Late Permian to Triassic times can be explained according to regional trajectories of extensional stress due to the activity of the North-Pyrenean fault zone.