JGR-Earth Science: Denudation rate changes along a fast-eroding mountainous river with slate headwaters in Taiwan from 10Be (meteoric)/9Be ratios

Kai Deng^1,2, Shouye Yang¹, Friedhelm von Blanckenburg^2,3, Hella Wittmann²

1 State Key Laboratory of Marine Geology, Tongji University, 200092 Shanghai, China

2 GFZ German Research Centre for Geosciences, Earth Surface Geochemistry, Telegrafenberg, 14473 Potsdam, Germany

3 Institute of Geological Sciences, Freie Universität Berlin, 12249 Berlin, Germany

Abstract

Thenovel ¹⁰Be (meteoric)/⁹Be system, where ¹⁰Be is delivered by precipitation and stable ⁹Be is released by weathering, provides denudation rates over weathering-erosion timescales. The new tool is applicable to quartz-poor lithologies, e.g. mafic rock and claystone, which are not readily accessible by the commonly used in situ-produced¹⁰Be in quartz. We provide a first application of this proxy to a tectonically-active mountainous river, the Zhuoshui River in Taiwan. Taiwan Rivers supply a disproportionately high suspended and dissolved flux to the oceans and are often underlain by fine-grained shale/slate. ¹⁰Be (meteoric)/⁹Be-derived denudation rates (D_met) from the Zhuoshui Catchment are highest in the slate-dominated headwaters (4-8 mm/yr), and much lower (1-2 mm/yr) along the mid-lower reaches with mixed lithologies. At the basin-wide scale, we find a poor correlation between D_met and basin-averaged channel steepness despite a small climatic gradient. Because large lithological heterogeneities exist in this basin, we invoke a lithological effect to explain this poor correlation. Relying on a revised stream power incision model that incorporates rock erodibility, the resulting lithology- and runoff- adjusted k_sn(k_Lrsn) can be reconciled with denudation rates with the highest erodibility predicted to prevail in the Miocene slate of low metamorphic grade and high fracture density. This model suggests that the lithological heterogeneity can alter the coupling between surface denudationand channel morphology.On a broader perspective, the successful application of the ¹⁰Be(meteoric)/⁹Be proxy shows its applicability as a tracer for erosion and sediment transport processes in fast-eroding mountain belts underlain by slate lithologies.

AGU Eos Editors’ Highlight on this paper!

https://eos.org/editor-highlights/meteoric-10be-reveals-lithological-control-on-erosion-rates

Full article：https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JF005251