First ESR chronology of the Duero river terrace system in Northern Spain

Abstract

Intraplate basins potentially preserve the most complete record of tectonic, geomorphic and climatic evolution within the interior of continents. In the Iberian Peninsula most of the largest Cenozoic sedimentary basins show a change from aggradation to degradation. Determining the cause of the transition from aggradation to degradation and how this was linked to tectonic, climatic, and geomorphic events hinges on the chronology of the fluvial network incision and excavation of the basins fills. Fluvial terrace staircases, as a product of river incision, provide a direct record of incision and are known to be the result of the combination of climatic changes and tectonic uplift. The incision of most of the Iberian Peninsula basins appears to have initiated in the Quaternary but the precise timing of its initiation is actually poorly known and constrained. In order to overcome the lack of chronologies for these basins, in the following study we started by studying the Duero basin and its terrace system. It is a major intracratonic basin bounded by Cenozoic structures and is characterized by a maximum of 16 terrace levels from +141-144 m to +8-10 m, with the present alluvial plain at +4-5 m (Pérez-González et al., 1994; Santisteban and Shulte, 2007). The only published ages for the Duero basin are by Moreno et al. (2012) who confirmed the potential of the Electron Spin Resonance (ESR) dating method applied on bleached quartz extracted from terrace fluvial deposits on the Arlanzón valley, a main tributary of the Duero River located in the NE area of the basin. In this work, ESR was systematically applied to the main river, the Duero River, dating 4 different terraces spanning from the high to the medium levels: T2 (+135m), T3 (+114m), T5 (+90m) and T10 (+41m). ESR dates are coherent with the analyzed terrace system and allow defining the onset and development of the Duero valley in the center of the basin. Additionally, these results also allow to reconstruct the incision response of the tributary system, comparing these ESR results with those published about the Arlanzón river in NE sector of the basin.