Timing of European fluvial terrace formation and incision rates constrained by cosmogenic nuclide dating

Abstract

Age constraints of late Cenozoic fluvial terraces are important for addressing surface process questions related to the incision rates of rivers, or tectonic and climate controls on denudation and sedimentation. Unfortunately, absolute age constraints of fluvial terraces are not always possible, and many previous studies have often dated terraces with relative age constraints that do not allow for robust interpretations of incision rates and timing of terrace formation. However, in situ-produced cosmogenic nuclides allow absolute age determination, and hence incision rates, of fluvial deposits back to 5 Ma. Here we present, cosmogenic depth profile dating and isochron burial dating of four different river systems in Europe spanning 12° of latitude. We do this to determine river incision rates and spatial variations in the timing of terrace formation. Isochron burial age constraints of four selected terraces from the Vltava river (Czech Republic) range between 1.00±0.21 to 1.99±0.45Ma. An isochron burial age derived for the Allier river (Central France) is 2.00±0.17Ma. Five terrace levels from the Esla river (NW Spain) were dated between 0.08+0.04/−0.01Ma and 0.59+0.13/−0.20Ma with depth profile dating. The latter age agrees with an isochron burial age of 0.52±0.20Ma. Two terrace levels from the Guadalquivir river (SW Spain) were dated by depth profile dating to 0.09+0.03/−0.02Ma and 0.09+0.04/−0.03Ma. The one terrace level from the Guadalquivir river dated by isochron burial dating resulted in an age of 1.79±0.18Ma. Results indicate that the cosmogenic nuclide-based ages are generally older than ages derived from previous relative age constraints leading to a factor 2–3 lower incision rates than previous work. Furthermore, the timing of terrace formation over this latitudinal range is somewhat obscured by uncertainties associated with dating older terraces and not clearly synchronous with global climate variations.