Combined unsteady denudation and climatic gradient factors constrain carbonate landscape evolution: New insights from in situ cosmogenic 36Cl

In situ cosmogenic nuclides are widely employed to quantify topographic and geomorphic landscape evolution. However, few studies are devoted to investigating possibly unsteady denudation. In this work the denudation rates of five surface bedrock and one depth profile are measured using in situ cosmogenic Cl-36 in different climate zones in China; cosmogenic Cl-36 is a powerful proxy for the surface denudation processes of carbonate landscapes in different climatic gradients since carbonates are more sensitive to climate change than silicates. Compiling previous worldwide surface denudation studies in different gradients, we find that: (I) denudation rate increases systematically with mean annual precipitation (MAP) in arid climatic zones (MAP lower than similar to 700 mm yr(-1)) and is dominated by long-term climatic gradients; (II) humid climatic zone (MAP greater than similar to 700 mm yr(-1)) denudation rates are about constrained to 34.1. 11.7 mm kyr(-1) by carbonate dissolution kinetics; and (III) denudation rate is also influenced by short-term physical erosion or abrupt erosive events. Accordingly, the reconstructed evolutionary history of the Guizhou depth profile results from either a relatively high denudation rate (55.5(-4.4)(+5.6) mm kyr(-1)) and long duration exposure (274(-147)(+120) ka), or an alternative a low denudation rate (0.8(-0.8)(+13.3) mm kyr(-1)) and a recent abrupt erosive event (13.0(-1.6)(+1.9) ka). These two possible solutions suggest that assumed long-term averaged denudation rate can conceal episodic erosion events. Given tectonic quiescence we propose that climate change might mainly control an erosive event during the last glacial termination (similar to 14 ka), which also implies that caution should be taken when determining the denudation rate of a landscape where climate change and/or tectonic activity plays an important role.