Abstract

The Cerdanya, Seu d'Urgell, Conflent and Rosello basins began to form in the Miocene, as a result of the dextral slip of the La Tet and La Tec faults that extend ENE and WSW across the eastern Axial Pyrenees. The first stage of sedimentation was followed by an episode of basin inversion, which was, in turn, followed by a second stage of sedimentation in the Late Miocene (Late Messinian) and Pliocene. Plant material fossilised during the sedimentation provides evidence of the development of the present Mediterranean climate with warm and dry summers and cold and damp winters.

Introduction

The present relief of the Eastern Axial Pyrenees is characterized by wide ENE–WSW oriented valleys and depressions (Cerdanya, Conflent, Rosselló) along which the main rivers of this area run (Segre, La Tec and La Tet rivers). Partially modified by the Quaternary glacial processes, this morphology was caused by the development, during the Neogene, of a horst and basin system which is bounded by E–W and ENE–WSW faults (Fig. 1). The most prominent are the ENE–WSW La Tet and La Tec fault systems, which are formed by NE–SW right-stepping en echelon faults and E–W faults that developed at the end of its western block and in the overstep zones of the NE–SW faults.

The Cerdanya, Seu d'Urgell and the Conflent basins are related to the La Tet fault (Fig. 1) and formed on the NW side of this fault, where major extensional E–W faults developed (Fig. 2).