Hillslope Denudation and Morphologic Response Across a Rock Uplift
Total Page：16
File Type：pdf, Size：1020Kb
EGU2019-8489 Hillslope denudation and morphologic response across a rock uplift gradient Main findings • We study a 10 km long transect in the Valensole Mio-Pliocene molassic Insights from the Valensole Plateau, Southeastern France formation at the SE Alpine front, using a high resolution LiDAR DEM and 1 1 2 1 1 1 3 1 cosmogenic nuclides Vincent Godard , Jean-Claude Hippolyte , Edward Cushing , Nicolas Espurt , Jules Fleury , Olivier Bellier , Vincent Ollivier , and Team Aster • We observe a systematic change in hillslope properties along the transect, 1 Aix Marseille Univ, CNRS, IRD, INRA, Coll France, CEREGE, Aix-en-Provence, France, with notably a localised sharp increase in hilltope curvature (CHT) and Non- 2 dimensional erosion rate (E*) BERSSIN, Institut de Radioprotection et de Surete Nucleaire, Fontenay-aux-Roses, France, Settings 3 Alps and Provence • This change is colocated with a deflection of the post-Pliocene surface of the Aix-Marseille Université, CNRS, MC, LAMPEA, Aix-en-Provence, France Miocene and Pliocene Valensole Plateau in SE France sedimentary series detrital sediments Quaternary Digne Neogene plateau and points to a possible gradient in rock uplift along the transect. Thrust Paleogene Cretaceous Anticline axis Jurassic • Metrics extracted from river profiles, such as normalized steepness indexes, Abstract Triassic Alpine units Bléone Understanding the modalities of the topographic response to tectonic and climatic forcings is a cornerstone of Earth Surface processes research. Recent methodological advances have revolutionized our ability to constrain the External crystalline Les Mées show little systematic variations along the transect massifs spatial and temporal context of these processes and quantitatively address the major questions associated with these forcings. First, the ongoing developments in high resolution topographic data acquisition and processing allow Internal domain 10 26 Gap Hercynian basement • Measured Be and Al concentrations in hilltop bedrock samples, allows to obtaining increasingly precise and detailed pictures of topographic surface properties. Second, the ability to constrain rates of landscape evolution from cosmogenic nuclides concentration measurements has bolstered our calibrate a relationship between denudation rates and E* understanding of surface processes dynamics. However, major challenges still remain regarding the evaluation of the combined response of the hillslope and fluvial landscapes components to these forcings. Similarly, only a limited * number of studies have convincingly combined the spatial (high resolution morphology) and temporal (cosmogenic nuclides denudation rates) perspectives on landscape evolution. In order to increase our knowledge of the joint • The E pattern is used to constrain fault geometry in a simple elastic Sisteron spatial and temporal dynamics of surface processes, we investigated the morphological response of hillslopes across a thrust structure within the Valensole Mio-Pliocene molassic basin located at the front of the French Southern fig. 2 dislocation model Asse Alps. A major fold and blind thrusts system has uplifted the northern edge of the Valensole Plateau during the Quaternary and is potentially still active. The Durance River has incised the Western edge of the Valensole Plateau, where Oraison • Our results highlight the potential of high resolution hillslope morphology to a series of small catchments are directly connected to the Durance base level. These catchments are aligned along a N trending axis perpendicular to the main structures and thus ideally located to record relative spatial variations Middle Durance Fault Valensole charaterize rock uplift gradients in slow deformation areas in rock uplift. Plateau We analyzed high resolution hillslopes topographic properties, using a 1-m resolution LiDAR Digital Elevation Model (IGN RGE). We extracted individual hillslope parameters and observed a significant increase in various metrics such Manosque as hilltop curvature, hillslope relief or non-dimensional denudation rates, which is consistent with the location of the main underlying thrust structure identified by seismic surveys. Additionally, we sampled bedrock at several hilltops Cosmogenic nuclides locations for cosmogenic nuclides concentration measurement and denudation rates calculation. The lithological diversity of the fluviatile Valensole conglomeratic formation in the studied area allows measuring different cosmogenic Constraints on denudation rates and link with hillslope properties Durance radionuclides (CRN) from a same sample : 10Be and 26Al from sandstone clasts and 36Cl from carbonate clasts. Calculated hilltops denudation rates ranges from 40 to 120 mm/ka. These CRN-derived denudation rates appear to be Aix-en-Provence Croix Lake te S significantly correlated with non-dimensional denudation rates extracted from the hillslope high resolution morphological analysis. The analysis of high resolution hillslope properties highlights the possibility to resolve short 1:1 wavelength variations in rock uplift, that would not be possible to unravel using commonly used channel profiles investigation methods. Our joint analysis of topography and geochronological data supports the present activity of the Verdon investigated Quaternary fault propagation fold located at the Southeastern alpine front. This kind of study is a powerful method that may bring complementary constraints to morphotectonic analysis on slip rate occurring on blind Sea active faults. Consequently, this quantification could be critical for seismic hazard assessment related to active fault sources. Mediterranean Steady state denudation Be 10 Al/ 26 Study area Cross section Constant exposure Sampling site Analysed basins and samplng sites Across analysed basins Methods Summit surface Hillslopes and channel profiles properties Al denudation rate (mm/ka) 26 IGN RGE 1m LiDAR DEM Extraction of hillslopes structure [10Be] (x103 at/g) 10Be denudation rate (mm/ka) Durance Convert E* pattern in denudation rate Anthropic disturbance Hillslope length and relief : LH, R /a) 2 usivity (m ff Di 2 /a 0.008 m Non-dimensional erosion rate Gradient (m/m) Cross section 2 /a 0.006 m Weathering limit 2 /a 0.004 m Denudation rate (mm/ka) Denudation rate (mm/ka) 2/a 0.002 m Rancure Hilltop curvature : CHT -1 Non dimensional erosion rate E* Hilltop curvature CHT (m ) Distance along profile (km) Non-dimensional Erosion rate Elastic dislocation * E =2CHTLH/Sc model E* pattern fitted with elastic dislocation model Marginal distributions for elastic dislocation model parameters Critical slope 1.0 0.8 0.6 0.4 1.0 0.8 0.6 Hilltop curvature Sc Available seismic surveys data synthesis 0.4 0.2 best fit model 900 Durance Summit post-Pliocene surface Individual hillslope profiles 800 Rancure Channel profiles analysis Hillslope dimensions 800 Seismic data synthesis 900 1000 Bléone Top of Oxfordian black marls m/n 800 Basement Elevation (m) Elevation (m) TWT to top of Oxfordian 900 2 R Asse 1000 Channel properties Elastic dicsolocation geometry inferred from MCMC sampling Distance along stream (m) χ (m).