257 / 2019-06-30 23:02:29

Particle size features of the aeolian calcarenite profile in Shidao Island, Xisha Islands, South China Sea, China

aeolian calcarenite, particle size feature, Shidao Island, Xisha Islands

Analysis of the particle size features of aeolian sand on the coasts of islands is an important tool for research efforts seeking to understand, for example, the formation and evolution of coastal landforms, recovery of paleocoastlines, and analysis of paleowind conditions and paleoclimatic and paleoenvironmental changes. Pleistocene aeolian calcarenite on Shidao, Xisha Islands are one of the rare aeolianite successions found in Asia. The aeolian origin of the calcarenite in the surface layer of Shidao Island has been determined through analysis of the sedimentary structure, depositional boundary, paleontological assemblage, and depositional sequence by numerous researchers. Nevertheless, there is almost no systematic analysis particle size features of the aeolian calcarenite profile in shidao island. The aeolianite deposits on Shidao Island contain five stages of aeolian biocalcarenites and four paleosols. The outcrop profile studied in this paper is the fourth–stage aeolian calcarenite, which is located on the west coast of Shidao Island. In this paper, on the basis of field surveys of the aeolian calcarenite profile of Shidao Island and a description of its sedimentary structural features, sampling and particle size tests and comparative analysis were conducted in order to determine the particle size features of different sedimentary units. The profile comprises a rift in the bottom of the profile, and an aeolian dune, which includes a topset unit and a foreset unit. The foreset bed is the main body of the aeolian dune, which comprises foreset bedding, monocline bedding, and lenticular bedding, reflecting the progradational sedimentary feature of bedding development of downwind sediments. Comparative analysis of particle size composition, particle size parameters, and particle size probability cumulative curves was conducted for the foreset unit using a particle size image analysis technique. The results show that the particle size characteristics are different in the deposit units of aeolian dune profile, the overall particle size is characterized by medium calcarenite, good sorting properties, more negative skewness, near symmetrical distribution, and medium kurtosis in its particle size probability curve. The particle size probability curve is composed of a mainly saltation component, with a missing rolling component and a low suspension component, and the slope of the straight line is steep. Three kinds of environmentally sensitive particle sizes were extracted using particle size-standard deviation curves. Using the particle size probability cumulative curve and sedimentary background analysis, it was inferred that the topset bed sediments were carried mainly by the northeastern monsoon and storm surges, and the foreset bed sediments were carried mainly by the northeast prevailing wind of the East Asian monsoon and by the southwestern monsoon.