Thick loess is deposited on the platform in the piedmont zone of Muling-Xingkai Plain (Muxing Plain), but the genesis of the Muxing loess is still unclear. The aims of this study are to analyze the grain size characteristics of Muxing loess collected from the cores of a typical borehole (ZK1) in the piedmont zone of Muxing Plain, and to verify its genesis. The Muxing loess is mainly composed of the particles with diameter less than 50 μm, with an average content of 92.48%. The coarse silt particles with diameter of 10-50 μm are the basic composition of aeolian sediments, and their average content is 44.34% for the Muxing loess, which is the mode class among the particles with different diameters. The grain size parameters and frequency curves are similar to those of the typical aeolian sediments. The distribution characteristic of the Muxing loess in the C-M scatter diagram is consistent with that of the Xi Feng loess. In addition, the discriminant analysis shows the Muxing loess mostly consists of aeolian sediments. Therefore, it can be concluded that the Muxing loess mainly resulted from aeolian deposition based on the grain size characteristics. Muxing Plain is dominated by the monsoon climate, and the wind-blown dusts are gradually deposited after being transported over long distances.

The developmental characteristics of groundwater flow system are not only controlled by formation lithology and groundwater recharge conditions, but also influenced by the physical properties of fluids. Numerical simulation is an effective way to study groundwater flow system. In this paper, the ideal model is generalized according to the fundamental characteristics of groundwater system in inland basins of Western China. The simulation method of variable density flow on the development of groundwater system in inland basins is established by using EOS9 module in TOUGHREACT numerical simulation software. In accordance with the groundwater streamline, the groundwater flow system is divided into three levels, which are regional groundwater flow system, intermediate groundwater flow system and local groundwater flow system. Based on the calculation of the renewal rate of groundwater, the analysis shows that the increase of fluid density in the central part of the basin will restrain the development of regional groundwater flow system, resulting in a decrease of the circulation rate from 32.28% to 17.62% and a certain enhancement to the local groundwater flow system, which increased from 37.29% to 51.94%.