A GIS method to identify flat surfaces and restore relict fluvial long‐profiles from terrace remnants gives new clues on how large basins respond to endorheic–exorheic transitions (Duero basin, Iberian Peninsula)

Abstract

Fluvial terraces are used as geomorphic indicators for deciphering long‐term landscape evolution. Knowing the distribution of fluvial terraces is essential for establishing former river profiles and their tectonic significance, for studying climate‐modulated processes of terrace development, or for defining fluvial network adjustments in response to sudden base‐level changes like those produced by fluvial captures. Multiple methods for automatic map production have been proposed based on the comparison of morphometric indices with those of the modern river course. Here we propose an alternative method to identify flat surfaces and scarps separating them from digital elevation models without setting comparisons with a modern river course and thus fully applicable to study flat landforms whatever their origin. Its application to the low‐relief landscape of the Cenozoic Duero basin has allowed the improvement of previous geomorphological maps and the analysis of fluvial network adjustments in response to a sudden base‐level fall after the opening of the Neogene endorheic basin towards the Atlantic Ocean. Reconstructed terrace long‐profiles suggest an initial episode of fast vertical incision followed by a period of repeated planation–aggradation–incision with the formation of 14 to 13 unpaired terrace levels. Changes observed in the pattern of terrace profiles are discussed with regard to changes in regional tectonics and base‐level variations. © 2019 John Wiley & Sons, Ltd.

Dates and rates of endo-exorheic drainage development: Insights from fluvial terraces (Duero River, Iberian Peninsula)

“…However, the age-height transfer curve reported for the Duero river in their work was supported on the few numerical ages available for the Arlanzón tributary, close to the source area of sediments in the Iberian Chain (Figure 1). Finally, an older opening age range of ~3.7-1.8 Ma has been recently reported based on an extrapolation of incision rates derived from strath terraces hanging at +53-48 m (360->230 ka), +34-27 m (57 ka) and +17-13 m (39-12 ka) between Pocinho and Barca d'Alva (Cunha et al, 2019), downstream of the Arribes knickzone, in the upper end of the Duero Lower Reach (DLR; -Rodríguez et al, 2020). The swath profile of maximum elevation shows the topographic signature of the LPS erosional surface, presumably linked to the initial emptying of the basin after the endo-exorheic transition.…”

“…Either a younger opening age for the Duero Basin compared to other Iberian basins (> 3 Ma according to Antón et al, 2019;~3.7-1.8 Ma according to Cunha et al, 2019;1.1-1.9 Ma according to Silva et al, 2017) and/or the resistant lithology that configures the Duero basin fringe (Struth et al, 2019) could explain the differences observed in fluvial entrenchment in response to sudden base-level lowering caused by an endo-exorheic transition. Here, we target a sequence of thirteen inset fluvial strath terraces formed in response to the Duero endo-exorheic transition, which are now hanging at heights up to +136-128 m above the modern floodplain (Rodríguez-Rodríguez et al, 2020; Figure 2).…”

“…Figure 2.-Geomorphological map of the fluvial terrace staircase developed by the Duero River upstream the Arribes knickpoint. Terrace sample site locations are shown both in the map and along the reconstructed former river profiles based on statistical analysis of terrace surface points extracted from a high-resolution digital elevation model (Rodríguez-Rodríguez et al, 2020). The swath profile of maximum elevation shows the topographic signature of the LPS erosional surface, presumably linked to the initial emptying of the basin after the endo-exorheic transition.…”

“…This model is consistent with an enhanced erosion in the Esla catchment allowing higher incision rates and total incision (highest terrace at +100 m) than in the Arlanza-Arlanzón system placed further upstream (highest terrace ~80 m; Figures10 and 11). Also, significant differences in terrace patterns and landscape dissection are observed in the main trunk(Rodríguez-Rodríguez et al, 2020), with the highest terraces only preserved upstream at the basin center (Figure2). At a basin scale, the relatively low average denudation rates derived from the upper terraces are consistent with a null or scarce transmission of the erosive wave nucleated at the opening site along the catchment at that stage.…”

Topographic, lithospheric and lithologic controls on the transient landscape evolution after the opening of internally-drained basins. Modelling the North Iberian Neogene drainage

“…This is independent on whether the opening is dominated by basin overfilling or by fluvial capture (piracy). The spillway and the just extended drainage basin then tend to adjust to the new base level (Howard et al, 1994) resulting in an upstream propagation of an erosion wave (e.g., Loget and Van Den Driessche, 2009;Struth et al, 2019;Rodríguez-Rodríguez et al, 2020a, 2020b. This retrogressive incision wave erodes the elevated low relief formed during the endorheic conditions.…”