Abstract:

Sediment grain size characteristics are of great significance in distinguishing aeolian landforms and sedimentary environments, determining transportation methods and dynamic conditions, controlling dune landforms, and restoring paleoclimate changes. This paper investigates the surface sediments in the nebkhas and parabolic dunes of the Tukai Desert, Xinjiang, China, analyzes the characteristics of grain size gradation and grain size parameters through mathematical statistics, and discusses the characteristics of sand dune grain size using the Sahu formula. Knowledge of the grain size characteristics of sediments can help to identify the material sources of desert sediments, explore the regularities of wind-sand flow, and enrich understanding of wind-sand activities. The results of this study indicate that the surface sediments of the nebkhas and parabolic dunes of the Tukai Desert are relatively coarse, being mainly composed of extremely fine sand, fine sand, medium sand, and coarse sand. The surface sediments of the nebkhas are also coarser than those of parabolic dunes. Furthermore, there are differences in the distribution of granules among the different landscapes. In the parabolic dunes, the content of fine sand and extremely fine sand are highest in the southern wing tail, whereas medium sand is most common in the north wing tail. On top of the nebkhas, the content of medium sand and fine sand is the highest, whereas the percentages of extremely fine sand and coarse sand are the highest at the bottom of the windward slopes. From windward slopes to the leeward slopes, the grain size characteristics of the surface sediments of the nebkhas and parabolic dunes tend to be associated with fine sand. The sand grains also tend to be fine from the bottom to the top of the slopes. The average grain size of the surface sediments of the parabolic dunes is greater than that of the surface sediments of the nebkhas, with the average values being 2.17 Ф and 1.89 Ф, respectively. The separation coefficients of the sand on the surface of parabolic dunes and nebkhas were similar, with the average values being 0.65 Φ and 0.64 Φ, respectively, belonging to the medium preference. The surface sediment skewness of both the parabolic dunes and nebkhas is 0.06 Φ, a nearly symmetrical distribution. The kurtosis values of the parabolic dunes and nebkhas were found to be 1.03 Φ and 0.99 Φ, respectively, belonging to medium peaks. A correlation was also found between the particle size parameters of the nebkhas and parabolic dunes. The average particle size has little correlation with the sorting coefficient, skewness, and kurtosis. However, there is a significant correlation between the sorting coefficient, skewness, and kurtosis. According to the Sahu discriminant formula, it was calculated that the Tukai Desert has a complex sedimentary environment, with the sediment formation environment being mainly aeolian and turbid. Distinctions in sand source, topography, wind dynamic conditions, and sand field characteristics, among other factors, contribute to the differences in the grain size characteristics of the surface sand materials of the sand piles of the Tukai Desert parabolic dunes and nebkhas, which have an impact on the desert sedimentary environment.

Key words: Tukai Desert, nebkhas, parabolic dunes, grain size characteristics, sedimentary environment