Tong Zhao

Cosmogenic nuclides (10Be and 26Al) erosion rate constraints in the Badain Jaran Desert, northwest China: implications for surface erosion mechanisms and landform evolution

Both tectonics and climate affect surface erosion and change the landform. Long-term surface erosion rates determined by in situ produced cosmogenic nuclides are useful quantitative constraints for landform evolution in geological time scale. Measurements of cosmogenic 10Be and 26Al in the granitic rocks exposed in the Badain Jaran Desert, give a mean erosion rate of 7.3 ± 2.6 m/Ma, which is an order of magnitude higher than those reported in other extremely arid regions. Tectonic activity is supposed to be the first order control on regional erosion rate by comparing the 10Be erosion rates of arid regions with different precipitation ranges and tectonic activities worldwide. However the higher erosion rates in the Badain Jaran Desert compared with other arid regions within the stable tectonic background were attributed to the wind erosion and periodically warmer and wetter climate since late Pleistocene. Besides, the estimated eroded mass flux of 7.8 × 104 t/y suggests that erosion products of bedrocks in the Badian Jaran Desert only contribute minor desert deposits, which indicates massive exogenous materials input to the desert.

Chemical and strontium isotopic characteristics of the rivers around the Badain Jaran Desert, northwest China: implication of river solute origin and chemical weathering

The chemical and strontium isotopic compositions of four major rivers (Heihe, Shule, Beida, and Shiyang) around the Badain Jaran Desert, northwestern China, were measured to understand the solute sources of surface water and rock weathering in the arid region. These rivers have high total cationic charge (TZ+) and total dissolved solids (TDS), averaging at 7379xa0μEq and 511xa0mgxa0l−1, which are significantly higher than the global river average. The increase in TDS and major ions (Na+, Cl−, and SO42−) and TDS concentrations from upper to lower reaches is ascribed to the evaporite dissolution and the effect of evaporation in the arid and semiarid areas. 87Sr/86Sr isotopic ratios of these rivers range between 0.71019 and 0.71628, with an average of 0.71328. The chemical and 87Sr/86Sr isotopic analyses indicate that three reservoirs (evaporites, carbonates, and silicates) contribute to the total dissolved loads. The contributions of the different reservoirs to the dissolved load are first calculated using a forward method in this area. The calculated results show that the dissolved cation load is dominated by carbonates weathering and evaporites dissolution, and their contribution account for about 80xa0% of the total dissolved cations for the rivers around the Badain Jaran Desert. The proportion of the dissolved cations from silicates weathering is 23.5, 10.8, 12.1, and 18.2xa0%, and the weathering rate of silicates is 0.81, 0.76, 2.04, and 0.93xa0tonxa0km−2xa0a−1 for Heihe, Shule, Beida, and Shiyang, respectively.