Basin formation at the end of a strike-slip fault: the Cerdanya Basin (eastern Pyrenees

Abstract: The Cerdanya basin was formed during dextral slip along the NE-SW La Tet fault (eastern Pyrenees) which formed a horsetail structure at its SW end. The resulting basin is clearly asymmetri-cal, formed by several basement blocks tilted towards the La Tet fault and limited by E-W faults. These faults absorbed the movement along the major strike-slip fault. The early basin evolution (Middle-Late Miocene) resulted from strike-slip, while the later evolution (Early Pliocene) involved a generally extensional regime. A variety of depositional environments developed in the basin during its early evolution: spatially restricted and widespread alluvial fan, distributary fluvial, marginal and open lacustrine. The structu-ral features of the basin that developed during this evolutionary stage differ from those described from most other basins related to strike-slip faulting. Despite this, the structural and sedimentary features of the Cerdanya basin fit the general model of strike-slip related basins. Numerous features which indicate crustal extension and graben formation are reported from areas affected by strike-slip faults. However, at present no detailed description of basin formation near the termination of strike-slip faults exists. This paper deals with a regional study of the Cerdanya basin that developed at the SW end of the La Tet strike-slip fault (Fig. 1). Extensional conditions at the ends of strike-slip faults can be explained by the existence of geometrical and mechanical irregularities that occur at fault terminations