Propiedades magnéticas de sedimentos del Triásico Medio- Jurásico Inferior de la Cordillera Ibérica Occidental

Abstract

A rock magnetic and palaeomagnetic study on two Middle-Late Triassic sections in the westernmost margin of the Iberian Ranges -that mostly consist of a thick sequence of interbedded mudstones and sandstones- and their Lower Jurassic top -dolomitized limestones- has been performed. Anisotropy of magnetic susceptibility thermomagnetic curves and hysteresis properties have been measured and the palaeomagnetic directions interpreted according to these analyses. Whereas the magnetic signal of the dolomitized Lower Jurassic limestone and some of the Triassic beds is unstable, multicomponent magnetisation behaviour has been observed in theTriassic red beds. The characteristic component presents high coercitivity and distributed unblocking temperatures up to 700-C (carried by hematite), showing both polarities and defining a consistent magnetic zonation. The NRM also contains lower unblocking temperature components with normal polarities. These are interpreted as result of the overlapping of a present day field component and an older overprint, probably related to the extensional phases of the Iberian Basin during the Cretaceous time. Primary remanence is better preserved in the fine-grained beds, showing a lower overlapping degree between the characteristic component and the high temperature overprint.