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Hydrological processes play important roles in soil erosion processes of the hillslopes. This study was conducted to investigate the hydrological processes and the associated erosional responses on the purple soil slope. Based on a comprehensive survey of the Wangjiaqiao watershed in the Three Gorges Reservoir, four typical slope gradients (5°, 10°, 15°and 20°) were applied to five rainfall intensities (0.6, 1.1, 1.61, 2.12 and 2.54 mm·min -1 ). The results showed that both surface and subsurface runoff varied greatly depending on the rainfall intensity and slope gradient. Surface runoff volume was 48.1 to 280.1 times of that for subsurface runoff. The critical slope gradient was about 10°. The sediment yield rate increased with increases in both rainfall intensity and slope gradient, while the effect of rainfall intensity on the sediment yield rate was greater than slope gradient. There was a good linear relationship between sediment yield rate and Reynolds numbers, flow velocity and stream power, while Froude numbers, Darcy-Weisbach and Manning friction coefficients were not good hydraulic indicators of the sediment yield rate of purple soil erosion. Among the three good indicators (Re, v and w), stream power was the best predictor of sediment yield rate (R 2 = 0.884). Finally, based on the power regression relationship between sediment yield rate, runoff rate, slope gradient and rainfall intensity, an erosion model was proposed to predict the purple soil erosion (R 2 = 0.897). The results can help us to understand the relationship between flow hydraulics and sediment generation of slope erosion and offer useful data for the building of erosion model in purple soil.

Feldspar dissolution is a common feature in clastic rock reservoirs of petroliferous basins and has an important influence on reservoir quality. However, the effect of feldspar dissolution on reservoir quality varies under different depositional environments and diagenetic systems. The study area in this paper is located in the Baikouquan Formation in the northwestern margin of the Junggar Basin, which is significantly influenced by feldspar dissolution. Based on the analyses of core and thin section observations, QEMSEM, XRD, SEM, CL, fluorescence, and image analysis software combined with logging and physical property data, this study shows that feldspar dissolution in the subaqueous distributary channel of a fan delta plain, which has good original physical properties and low mud contents, significantly improves the properties of the reservoir. The main reasons for this are as follows: (1) the sedimentary facies with good original properties and low mud content is a relatively open system in the burial stage. The acidic fluids needed for feldspar dissolution are mostly derived from organic acids associated with the source rocks and migrate to the good-permeability area of the reservoir; (2) the by-products of feldspar dissolution, such as authigenic clay minerals and authigenic quartz, are transported by pore water in a relatively open diagenetic system and then precipitated in a relatively closed diagenetic system; and (3) the clay minerals produced by feldspar dissolution in different diagenetic environments and diagenetic stages have different effects on the reservoir. When the kaolinite content is less than 3%, the illite content is less than 4%, and the chlorite content is less than 12%, the clay minerals have a positive effect on the porosity. These clay minerals can reduce porosity and block pore throats when their contents are larger than these values.

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