Abstract
Abstract. We report measurements performed during two complete flow seasons on the Urumqi River, a proglacial mountain stream in the northeastern flank of the Tianshan, an active mountain range in Central Asia. This survey of flow dynamics and sediment transport (dissolved, suspended and bed loads), together with a 25-year record of daily discharge, enables the assessment of secular denudation rates on this high mountain catchment of Central Asia. Our results show that chemical weathering accounts for more than one-third of the total denudation rate. Sediment transported as bed load cannot be neglected in the balance, given that sand and gravel transport accounts for one third of the solid load of the river. Overall, the mean denudation rates are low, averaging 46 t × km−2 × yr−1(17–18 m Myr−1). We furthermore analyse the hydrologic record to show that the long-term sediment budget is not dominated by extreme and rare events but by the total amount of rainfall or annual runoff. The rates we obtain are in agreement with rates obtained from the mass balance reconstruction of the Plio-Quaternary gravely deposits of the foreland but signicantly lower than the rates recently obtained from cosmogenic dating of the Kuitun River sands, west of the Urumqi River. We show that the resolution of this incompatibility may have an important consquence for our understanding of the interplay between erosion and tectonics in the semi-humid ranges of Central Asia.
Highlights
Sediment transport in rivers remains an essential topic of research in earth sciences
In regions such as Central Asia where rainfall is essentially orogenic and much lower than in the Himalayas, for instance, our study and long-term denudation rates would indicate that the Tianshan mountain range is more probably in a regime where there is no dynamic equilibrium between denudation and uplift
Our survey of the Urumqi River enables us to draw several conclusions regarding the dynamics of erosion and sediment transport in the high mountains of Tianshan
Summary
Sediment transport in rivers remains an essential topic of research in earth sciences. We hereafter report a two-year survey on a braided stream in the Chinese Tianshan mountain range: the Urumqi River We use this survey together with a 25-year record of discharge to perform a mass balance, derive erosion rates in a glacial catchment and discuss the respective contribution of mechanical and chemical weathering to denudation. The Tianshan mountain range is a place where it is possible to survey sediment transport, both dissolved, suspended and bed load, using conventional equipment (Metivier et al, 2004; Meunier et al, 2006a), while tackling questions of geodynamic significance (Avouac et al, 1993; Molnar et al, 1994; Metivier and Gaudemer, 1997; Charreau et al, 2011; Poisson and Avouac, 2004)
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