Incision and dissection of the Ebro basin: spatial and temporal constraints on landscape development

A striking feature in northern Spain is the Ebro basin at over 80,000 km2 in area lying just south of the Pyrenees. It is dissected by the Ebro River and its major tributaries from the Pyrenees and Iberian Chain. The basin was closed during the Oligocene progressively filling with sediments shed from the surrounding mountains, creating a local base level over 800 m. The breaching of the basin connected the Ebro River with the Mediterranean, leading to a wave of incision into the basin and possibly the surrounding orogens, however the timing of this breach is still under debate. Several different fluxes of siliciclastics into the offshore Valencia trough have been attributed to evacuation of the Ebro basin sediments at various times from the late Miocene to the Pleistocene. This has lead to a variety of internal (i.e. lake overtopping) and external (i.e. erosional wave due to the Messinian Salinity Crisis) drivers for the breaching to be proposed. It has also been argued that the rather rugged relief seen in the Pyrenees despite being effectively inactive for the past 20 Ma is due to propagation of incision from the Ebro Basin, though others have argued against this. So far quantitative attempts to date timing of incision have lacked the temporal resolution necessary to detect less than 2 km of unroofing. This project aims to investigate the timing and rate of dissection and incision of the Ebro Basin and surrounding areas through the application of 4He/3He thermochronometry. Our results will not only determine the timing and driver of the opening of the Ebro basin, but also give important new information on the development of relief in post-orogenic stages and the response of a landscape to base level lowering.