Quantification of fluvial incision in the Duero Basin (NW Iberia) from longitudinal profile analysis and terrestrial cosmogenic nuclide concentrations

Abstract

The Duero Basin is one of the largest Cenozoic basins in Iberia and contains a relatively well-preserved sedimentary infill. The top of the sedimentary sequence crops out at elevations up to 900m above sea level. The present-day basin drains to the Atlantic Ocean via the Duero River through the Arribes Gorge, but during the Cenozoic the basin experienced a long endorheic period marked by the formation of evaporites. The time the basin opened to the Atlantic Ocean and the formation of the modern Duero River drainage system remains poorly constrained. In this study we quantify the spatial distribution of river incision within bedrock and sedimentary units by comparing the nearly relict higher reaches with the lower deeply incised reaches of the tributary system. Results show an abrupt increase in stream incision westward, reaching a minimum bedrock incision depth of 600m in the Arribes Gorge. Using cosmogenic 10Be and 21Ne data we estimate exposure ages for erosion surfaces at various levels in the incised Duero River. The cosmogenic nuclide dataset suggests that the final 2–300m of fluvial incision in the Arribes Gorge occurred at a rate of 2–3mm/yr over the last ~100ka.