Climatic and tectonic controls on fluvial incision and aggradation in the Spanish Pyrenees

The influences of tectonic and climatic changes on upland river systems are investigated using data from Plio-Pleistocene terraces of the Rio Cinca ri ver in the southern Pyrenees. This river runs transverse to the main thrust fault structures and is a major conduit for sediment delivery to the Ebro Basin. Detailed field mapping, combined with long-profile and palaeohydraul ic reconstructions, yields a comprehensive picture of changes in palaeorive r character during the Plio-Pleistocene. As the area is over 150 km from th e basin outlet in the Mediterranean Sea, changes in base level are unlikely to have influenced terrace development. Although tectonic activity has exe rted a strong control on the position of the river, the main period of thru st propagation pre-dates the terraces and activity has waned from the Plioc ene through to the present. It is concluded that the main control on incisi on in this area is climate, through its influence on sediment supply. River s which are starved of sediment by climate change will have the power to in cise, whereas aggradational phases are linked to periods of increased sedim ent flux.