Denudation Rate Controls along a Fast-eroding Mountainous River with Slate Headwaters from Meteoric 10Be/9Be Ratios
Abstract
Small mountainous rivers are well-known for the disproportionately high sediment fluxes, and thus quantification of their contribution to global denudation is of great importance. In most cases, in situ 10Be is used to reveal millennial-scale erosion. However, in the fast-eroding (>1 mm/yr) Taiwan Island, where quartz-poor slate dominates in the alpine region, in situ 10Be-derived denudation rates (Dinsitu) may not fully represent basin-wide erosion processes. The new denudation rate proxy from meteoric 10Be/9Be ratios integrates over all lithologies and hence provides an alternative choice. This proxy combines meteoric 10Be deposited at Earth´s surface with a largely known atmospheric flux and stable 9Be released from rocks by weathering.
Sediments were collected from mountain headwaters to floodplain along the Zhuoshui River, the longest river in Taiwan, in two years. Resulting 10Be/9Be ratios show a good consistency between different years. The meteoric 10Be-derived denudation rates (Dmet) are the highest in the slate headwaters (4-8 mm/yr), and agree with the range of published long-term exhumation rates since 0.5 Ma. Along the mid-lower reaches with mixed lithologies, both Dmet and Dinsitu are much lower and within a similar range of 1-2 mm/yr. Focusing on the slate headwaters, our Dmet together with published Dinsitu in Taiwan show a lithology-dependent and non-linear correlation with normalized channel steepness (ksn). The correlation shows a steeper gradient in slate-dominated regions compared to that from the other data, which we relate to the lower critical threshold for detachment and higher erosional efficiency in slate. In addition, the downstream decreasing trend of Dmet is attributed to the increasing influence of more slowly eroding (sandstone-dominated) lithology, evidenced by a positive correlation between Dmet and the areal percentage of the upstream slate. Altogether, our results are consistent with independent erosion proxies and topographic analysis, and hence show the potential of the new meteoric 10Be/9Be proxy to trace erosion and sediment transport processes in fast-eroding areas underlain by quartz-poor lithologies.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP21D2270D
- Keywords:
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- 1815 Erosion;
- HYDROLOGYDE: 1820 Floodplain dynamics;
- HYDROLOGYDE: 1825 Geomorphology: fluvial;
- HYDROLOGYDE: 1862 Sediment transport;
- HYDROLOGY