Study On Sediment Characteristics And Provenance Of Sandy Land In Poyang Lake

The sandy land in Poyang Lake is a typical aeolian land in a subtropical humid area.Its ecological restoration and environmental protection are important components of regional ecological civilization construction and have always been a hot topic of research.Currently,environmental restoration of sandy land in Poyang Lake is only concentrated in small areas,and there is a lack of comparative studies of different sandy land sediments in different regions.This paper studied the sediment characteristics of Hukou County,Duchang County,Lushan County,Yongxiu County,and Xinjian District on Poyang Lake through grain size,heavy mineral,and wind condition analyses,and investigated the sedimentary environment and provenance of the sediments.The following findings were obtained from the research:(1)The sediment grain size in Poyang Lake sandy land is primarily composed of medium sand,fine sand,coarse sand,and silty sand,accounting for over 96% of the total content in Poyang Lake sandy land.The Mz ranges from 1.01 to 3.36Φ,with a mean of 1.80Φand a mean of Sd of 1.06,indicating poor sorting.Sk is positively skewed,and Kg is very sharp.The surface content of clay,silty sand,very fine sand,fine sand,and very coarse sand in Poyang Lake sandy land is higher than that in the 20-40 cm depth,while the content of medium sand and coarse sand is lower than that in the 20-40 cm depth.The depth of Mz,Sd,Sk,and Kg in the surface sediments is higher than 20-40 cm,indicating that the surface sediments have more fine particles and poor sorting,and the sand particles tend to be extremely positive with sharp peaks.Fixed dunes,semi-fixed dunes,and mobile dunes in Poyang Lake sandy land are aeolian deposits.The river flat is dominated by fluvial action and supplemented by wind erosion.Wetland grassy flat is formed under the combined action of wind and water power.The sediment source of dunes is mainly in situ sand,while the sediment source of river flat and wetland grassland flat is mainly from adjacent river flat and lake flat,both of which are proximate sediments.In terms of spatial variation,wind regime and grain size in Poyang Lake sandy land showed a certain distribution pattern along the prevailing wind direction(northerly wind).The annual average wind speed and wind frequency of sand wind in Poyang Lake sandy land increase from south to north;the sand sediment decreases successively,and the average of medium sand increases successively.The mean Mz values of Yongxiu,Lushan,Duchang,and Hukou decreased successively,and the mean Sd values of Xinjian,Yongxiu,Lushan,Duchang,and Hukou decreased successively,indicating that the grain size of sediments along the prevailing wind direction became smaller and better.This is closely related to the increasing average wind speed and frequency of sand-driving wind from south to north in Poyang Lake sandy land.(2)The main heavy mineral assemblages in the sediments of Poyang Lake Sandy land are primarily composed of ilmenite,white ilmenite,tourmaline,zircon,hematite,epidote,and anatase.There are also small amounts of garnet,magnetite,kyanite,rutile,and others,reflecting the parent rock types that are mainly composed of neutral and basic magmatic rocks,acid magmatic rocks,and metamorphic rocks.The heavy mineral characteristic index indicates that amphibolite and granulite are the main source rock types and the characteristics of near-source deposition.Based on comprehensive analysis,the main provenance of sandy sediment in Poyang Lake is the Neoproterozoic Shuangqiaoshan group in the Jiulingshan and Gongshan regions on both sides of Poyang Lake,as well as the mesobaric and acidic intrusive rocks in different periods,supplemented by the mesobaric rocks in the Ganjiang River Basin.In terms of spatial distribution,the maximum value of heavy mineral content and characteristic index is close to the source area.