Fluvial bedrock gorges as markers for Late-Quaternary tectonic and climatic forcing in the Southwestern Alps

The interplay of geology, climate and tectonics on river incision: the example of the High Verdon Gorges, Southwestern French Alps

“…These authors considered that the HVG constitutes a abnormally high local base level for the upper Verdon. The HVG forms a limestone (Tithonic) lithological knickpoint which likely mitigates the propagation of incision upstream, as observed in several studies [Crosby and Whipple, 2006, Jansen et al, 2010, Bishop and Goldrick, 2010, Cardinal et al, 2022. Therefore, undergoing slower incision, the upper Verdon mean elevation remains high, which makes it vulnerable to capture by the more competitively erosive surrounding catchments.…”

“…A total of 11 samples were collected along a 12 mhigh polished surface in the Samson Corridor, which gave CRE ages ranging from 15 to 45 ka. These data were already presented by Cardinal et al [2022], where the authors made a conservative choice to consider only one regression line for deriving incision rates. As in the present study, to constrain more precisely the timing of incision in the HVG, the code was allowed to use three regression lines in order to obtain incision rate variations.…”

“…At the same period, a sequence of rock falls in the La Mescla site can be inferred, suggesting a period of increased downcutting at that time. Following the regional interpretation proposed by Cardinal et al [2022], several rivers connected to the Last Glacial Maximum (LGM) glaciation in the SW French Alps underwent a period of enhanced fluvial incision following the main glacier retreats [19-17 and 14 ka; Rolland et al, 2019]. From these results, it seems that the Verdon River may have undergone the same evolution, but since only three ages younger than 20 ka are obtained in the entire dataset, it remains difficult to infer any detailed post-glacial history of the HVG with confidence.…”

“…Incision rates in the Samson Corridor (0.2 mm/yr) is twice as high, as in neighbouring catchments for the recent period covering the last ca. 40 ka [ranging from 0.15 and 0.28 mm/yr; Cardinal et al, 2022]. This can be ascribed either to differential tectonic motions (with respect to the lower Verdon Gorges and Valensole plateau) or to delayed incision of a steep, disequilibrium river profile that might have accumulated between several glacial cycles [Rolland et al, 2017].…”

“…previously covered by Quaternary glaciers [Brisset et al, 2015], while its outlet in the Durance river is near the junction between the Alpine deformation front and the Valensole foreland basin (Figure 1B). In this paper, we present new, and use some published [Cardinal et al, 2022], 36 Cl Cosmic Ray Exposure (CRE) datings of river-polished surfaces in the HVG and interpret them for the recent (Late Quaternary) period, and discuss a long-term (Pliocene to Quaternary) evolutionary scenario of the Verdon River in its Alpine and Mediterranean context.…”