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Using scanning electron microscope (SEM), the modification and superposition of quartz surface textures of sandy sediments in the Taklimakan Desert are observed and analyzed. Based on field occurrence characteristics, sand materials can be divided into river-sand, dune-sand and stratum-sand. The features of surface texture of quartz grains are as follows:(1) On quartz grain surfaces in river-sands, the imprints by mechanical actions of glacier and running water are retained, i. e., conchoidal fracture, straight steps, arcuate steps. V-shaped depression, striation and so on. The imprints by chemical action are slighter.(2) The quartz grains in dune-sands can be divided into newer and older eolian sands. On the surfaces of newer eolian quartz sands, the imprints by glacial and river actions are clearly retained and the solution-precipitation textures are the results of low-energy chemical environment. The grain surfaces of older eolian quartz are covered with wind abrasion textures, and the earlier imprints on the surfaces caused by glacial and running water actions have been strongly rounded. This type of quartz sand often develops honeycombed hollows, scaly exfoliation surface and solution-precipitation textures in high-energy chemical environment. It should be indicated that the content of older eolian quartz grains in dune-sands is very low.(3) The quartz grains of stratum-sands can also be divided into newer and older eolian sands. Their surface patterns and textures are respectively similar to the newer and older eolian quartz grains in dune-sands.Above features show the sand materials of the Taklimakan Desert are modified by wind abrasion and chemical weathering after they are transported to the desert area by glacier and running water.According to observation and analysis under SEM, we can find that the surface textures of quartz grains in river-sands are mainly compound imprints by glacial and subaqueous mechanical actions. The quartz grains of dune-sands, based on the strength of eolation to surface textures formed in earlier period, can be divided into older eolian quartz sands and newer ones. The older ones suffer a lasting abrasion by wind, so that the surface textures caused by glacial and river actions in earlier period have been rounded, or wind abrasion textures such as pitted surface and dish-shaped concavity, etc. are superposed on their surfaces. This makes the earlier surface textures unclear. On the newer ones, imprints by glacial and river actions are clear, because the time in which these imprints are modified by wind is not long. The surface texture features of quartz grains in subsurface stratum-sands are similar to those of dune-sands. The features as above further confirm the discussion-the recent rivers still supply the Taklimakan Desert with sand.Chemical solution-precipitation textures of quartz grains surface in dune-sand and stratum-sand are mainly products of low-energy chemical environment, i. e., they are solution pits, solution holes and tiny SiO2-precipitates. This is related to the climate condition that it is dry and the temperature varies greatly between day and night in the Taklimakan Desert. However, in few area, such as Mazhatag Mountain Region and the core T. C. No. 1 (bellow 78m), products of chemical weathering in high-energy chemical environment are often found, i. e., honeycombed surface and scaly exfoliation chemical solution textures developed on quartz surfaces of the sand samples. The reason is that part of sand materials in the Mazhatag Mountain Region come from the bedrock of Tertiary System, and in Tertiary Period, relative warm-humid climate had appeared.

Study on the Texture Features of Quartz Grain Surfaces in Sandy Sediments of the Taklimakan Desert.