Speaker
Description
Landscape evolution is a fundamental and vital topic in natural geography science, which is of great significance for understanding Earth’s dynamics, climate change, geohazard prevention and human habitability. Surface denudation, referring to the sum of chemical weathering and physical erosion, is an essential process to drive landscape shaping and transformation. In details, chemical weathering refers to the process of the alteration of bedrock to saprolite by chemical reactions, after which saprolite can be mechanically disrupted into mobile soils that can be transported from hillslopes to streams and rivers by physical erosion. Recently, in-situ 10Be depth profiling provides a powerful perspective for quantifying the surface denudation rates and studying the historical records of landscape denudation along geologic timescales. When combining in situ 10Be analysis with geochemical methods such as mass balance calculation using an immobile element within a weathering profile, one can explicitly extract the respective proportion of chemical weathering and physical erosion from a certain 10Be-derived denudation rate.
Therefore, this study conducted the measurement of geochemical compositions and in situ 10Be concentrations of a granitic weathering profile from a high-relief landscape on the eastern margin of Tibetan Plateau. Geochemical mass balance calculation suggests that chemical weathering mainly occurred in the saprock zone. 10Be concentrations in the soil are significantly lower than those in the uppermost saprolite, suggesting that the soil should be an external cover rather than an in situ weathering product from the underlain saprolite. Depth variations of the measured 10Be concentrations cannot match the steady-state modeling curve, indicating that the weathering profile should be involved with an unsteady-state denudation regime. Variation of 10Be concentrations in the saprolite/saprock zone at the shallow depths ( < 200 cm) that should have been controlled by the spallation of neutrons, instead, show an obvious signal of significant muonic production, implying that this layer should be derived from a deeper part that was suddenly exposed to the surface in a certain timing in the past by an abrupt denudation event such as landsliding. Finally, we proposed a conceptual model involved with unsteady denudation incorporating a landslide event. This model well explains the depth variation of 10Be concentrations, which yielded best-fitting results for the denudation rate of weathering profile (D) is 2.0 g m-2 yr-1, the occurrence time of landslide (t) is 11.6 kyr ago, and the depth of landsliding surface (XL) is 4.0 m. Together with the geomorphic parameters from traditional GIS-based analysis, this study may provide new insights into the coupling of chemical weathering and physical erosion under contrasting denudation regimes and the response of landscape evolution to tectonic forcing and, probably, the prediction of potential landslides in tectonically-active regions.
| Student Submission | Yes |
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