The Age,Origin,Climatic And Environmental Significance Of The Zheji Sand Hill In Hukou County,Jiangxi Province

Zheji Sand Hill is located in the north of Hukou County,JiangXi Province,on the south bank of the Yangtze river.The Quaternary in the area is well developed,the genetic types are complex,As a unique landscape around Poyang Lake,the Sand Hills have aroused great interest of scholars.Therefore,in order to understand the reason why the Sand Hills are distributed here,we should clarify their forming times and forming reason.Taking Zheji Sand Hill as the research objects,a large number of geological surveys and field measured sections were carried out in the field.Based on the studies of sedimentary strata,stratigraphic age,paleoclimate change,sediment source and tectonic evolution,etc.,the formation times,origin,development process and climatic and environmental changes of the Sand Hills are as follows:(1)On the basis of systematic survey and sampling to the profil,this paper measured the photoluminescence age of Zheji Sand Hill,and obtained the age of20.8ka-28.1ka,combined with the age of the surrounding Sand Hills.The author thinks that Zheji Sand Hill began to develop before 28,100 years,which is equivalent to the last interglacial period(MIS3).(2)For the cause of formation of the Sand Hills,by analyzing the spatial distribution,particle size characteristics,bedding feature,lithological characteristics,particle size scatter diagram,particle size image diagram,function discriminant and other characteristics of the Sand Hills,the forming reasons of Zheji Sand Hill can be judged as aeolian,and the clay interlayer in the Sand Hills indicates that the climate has fluctuated.(3)The development process of Zheji Sand Hill can be divided into three stages as a whole: During the interglacial period of the last glacial period(before 26ka),the early and middle periods of the Sand Hills around Poyang Lake were dominated by loess accumulation,and the bog peat was developed in the late period,the sediments formed in this period served as the sedimentary basement of Zheji Sand Hill.The ice peak period of the last glacial period(26-15ka)was the period of rapid development of the Sand Hills,the water level of the lake drops about 100 meters,and the exposed sediments at the bottom of the lake provide abundant material sources for the Sand Hills.The strong winter wind blows from the north to move the sediments to the downwind to accumulate the Sand Hills.Since 15 ka,in the early period(15ka-13ka),the climate has become warmer and wetter,sea level and lake level has risen,and the rainfall has increased,and some fine clay particles have been deposited in the sand mountain due to the warming environment.In the late period(since 13ka),the climate became cooler,the sediments became coarse relatively,and weathering and denudation combined to form the sand mountain cover.Periodic environmental changes have created today's Sand Hills.(4)The climatic and environmental characteristics during the development of Zheji Sand Hill: Zheji Sand Hill began to develop in the last interglacial period.In MIS3 b stage,the climate was relatively cold in the last interglacial period,the sea level declined,the coarse particles content of the sediments increased,a lowsporopollen concentration,and sparse coniferous forest as the main vegetation.In MIS3 a stage,the temperature rose,sea level rose,wetlands and swamps had developed,the vegetation were frondent,and the main species in the forest were quercus,chestnut,oak,castanopsis,etc.,indicating that the summer monsoon was strengthened and the climate was warm and humid in this period.During the ice peak period of the late glacial period,the climate was dry and cold,the winter monsoon was prevailing,the content of coarse particles in the sediment increased,the magnetic susceptibility of the sand layer was extremely low,the sporopollen content was very small,and the vegetation was sparse.The sea level rose to the current level in the early stage of the last late ice stage,the climate was warm and humid,the deciduous broad-leaved forest were prevailing,and the sediments were dominated by clay.The climate fluctuated in the the last stage of the last late ice stage,the sediment particles changed from small to big,and the temperature decreased slightly.