Study On The Characteristics And Causes Of Aeolian Carbonate Outcrop Profile In Xisha Shidao

Shidao is located on the reef plate of Xuande atoll in the Xisha Islands.It has an elevation of 13.8m and is the highest island in the middle of the Xisha Islands.It is also the only exposed Aeolian carbonate island in the South China Sea.In this paper,through the actual investigation of the Shidao outcrop profile,the outcrop profile samples were taken and the outcrop profile was described in detail.The collected samples were analyzed by particle size and the ¹⁴C age of the sample was measured using an accelerator mass spectrometer?AMS?.Get the following conclusions and understanding.?1?The outcrop profile of the Shidao aeolian carbonate is located on the west side of the Shidao Island.There is an anticline on the north side of the profile,and there is a monoclinic bedding,a trough-like staggered bedding,and a lenticular staggered bedding.,High-angle wedge-shaped staggered layering.These bedding tend to be about 225°,indicating that the prevailing wind direction and wind direction are large,even as high as 34°,which conforms to the characteristics of eolian deposits.?2?According to the grain size and sedimentary structure,the Shidao wind carbonate profile is divided into sand dunes and reef plates.The dunes are composed of top and front mounds,respectively,and the former layers contain monoclinic and interlaced layers.Science,wedge-shaped staggered layering,lenticular staggered layering and many other types of bedding.The top layer is dominated by coarse-medium sand crumbs,with the coarsest grain size and dominated by skip components.The wedge-shaped staggered bedding and monoclinic staggered layers are dominated by medium-fine sand crumbs;lenticular interlacing Sand crumbs are the main grade.The overall particle size characteristics are dominated by jumping components,with more than 90%in content,lack of rolling components,low content of suspended components,straight line inclination of 50°to 70°,and good sorting,which is in line with the characteristics of eolian sand.?3?There are three kinds of environmentally sensitive particle size components in the outcrop profile of Shidao:the environmental sensitive particle size component?1?<297.3um,its source is related to the summer monsoon;the environmental sensitive particle size component is 2297.3⁸40.9um The sources are related to the northeast monsoon;the environmentally sensitive particle size fraction?3?>840.9 um,and the source is dominated by the northeast monsoon and storm surge effects.?4?The paleowind velocity at the formation of the outcrop profile of the Shidao aeolian carbonate rock may be around 8.54 to 10.79 m/s.?5?The formation of the outcrop profile of aeolian carbonate formed in Shidao was not earlier than 4210±30a,B.P.?6?The source of its source may come from the ancient islands and its seven Lianyu.?7?The northeast monsoon of the East Asian monsoon and the alternating of the southwest monsoon and the southwest monsoon make the outcrop pattern of the Shidao outcrop,the interlaced staggered bedding,the lenticular staggered bedding,and the wedge-shaped staggered bedding alternate.This paper clarifies the bedding profile of the Shidao Outcrop section and the grain size of each sedimentary unit;gives the possible time and provenance of the Shidao outcrop profile;explains the genetic features and dynamic characteristics of the Shidao outcrop profile;The formation mechanism of the formation and the changes of East Asian monsoon since the late Pleistocene provide evidence.