Weathering-limited hillslope evolution in carbonate landscapes

Abstract

International audienceUnderstanding topographic evolution requires integrating elementary processes acting at the hillslope scale into the long-wavelength framework of landscape dynamics. Recent progress has been made in the quantification of denudation of eroding landscapes and its links with topography. Despite these advances, data is still sparse in carbonate terrain, which covers a significant part of the Earth's surface. In this study, we measured both long-term denudation rates using in situ-produced Cl-36 concentrations in bedrock and regolith clasts and surface convexity at 12 sites along ridges of the Luberon carbonate range in Provence, Southeastern France. Starting from similar to 30 mm/ka for the lowering of the summit plateau surface, denudation linearly increases with increasing hilltop convexity up to similar to 70 mm/ka, as predicted by diffusive mass transport theory. Beyond this point denudation rates appear to be insensitive to the increase in hilltop convexity. We interpret this constant denudation as indicating a transition from a regime where hillslope evolution is primarily controlled by diffusive downslope regolith transport, toward a situation in which denudation is limited by the rate at which physical and chemical weathering processes can produce clasts and lower the hilltop. Such an abrupt transition into a weathering-limited dynamics may prevent hillslope denudation from balancing the rate of base level fall imposed by the river network and could potentially explain the development of high local relief in many Mediterranean carbonate landscapes. (C) 2016 Elsevier B.V. All rights reserved

Chemical Versus Mechanical Denudation in Meta‐Clastic and Carbonate Bedrock Catchments on Crete, Greece, and Mechanisms for Steep and High Carbonate Topography

“…In many regions, carbonates form high cliffs and topography in comparison with other sedimentary and sometimes magmatic and metamorphic rocks (Ford & Cullingford, 1976). This observation is ubiquitous throughout the Mediterranean (Godard et al, 2016). For example, on the island of Crete, the landscape is dominated by high and steep carbonate massifs that define the backbone of the island, whereas areas underlain by silica-rich metamorphic units exhibit lower topography and gentler slopes (Figure 1).…”

“…Stone et al () first established the use of the 36 Cl cosmogenic nuclide to determine bedrock denudation rates in limestones. Previous studies of 36 Cl denudation rates have focused on exposed bedrock denudation rates, where dissolution is the dominant lowering process (Godard et al, ; Schaller et al, ; Thomas et al, ; Xu et al, ). However, quantification of carbonate denudation at the catchment scale is needed to integrate the effects of mechanical denudation processes along hillslopes and channels and to understand its impact on relief generation.…”

“…Stone et al (1994) first established the use of the 36 Cl cosmogenic nuclide to determine bedrock denudation rates in limestones. Previous studies of 36 Cl denudation rates have focused on exposed bedrock denudation rates, where dissolution is the dominant lowering process (Godard et al, 2016;Schaller et al, 2005; Thomas Creutzburg (1977) with faults and outlines of sampled basins for catchment average denudation rates. (c) Cumulative hypsometric curve of the main lithologies on Crete.…”

Hillslope denudation and morphologic response across a rock uplift gradient

“…The narrow floodplains present in our working area were delineated following the approach proposed by Clubb et al (2017). Hilltops were then identified as the intersecting margins of basins over all range of stream orders and curvature 190 was computed at every hilltop pixel by fitting a quadratic surface over a 30 m wide window (Hurst et al, 2012;Godard et al, 2016). Flow was routed downslope from hilltop pixels to the channels using the algorithm of Mitasova et al (1996), and the resulting flowlines were used to compute hillsope relief and length (Hurst et al, 2012;Grieve et al, 2015Grieve et al, , 2016a.…”

“…Only a handful of studies have actually attempted to reconcile CRN-based denudation data with topographic metrics extracted from High Resolution DTMs into a GTL-based physical framework (e.g. DiBiase et al, 2012;Hurst et al, 2012Hurst et al, , 2013bGodard et al, 2016Godard et al, , 2019Neely et al, 2019).…”