Unveiling Holocene Coastal Aeolian Environment: A Record From The Coastal Dunes At Changle, Fujian

The sand dunes widely distributing along Fujian’s southeastern coast are the products of the interactions among the land,ocean and atmosphere.Sea level change and regional climate play a critical role in the development of coastal sand dunes.Based on the chronology derived from the optically stimulated luminescence(OSL) method,the sedimentary structure derived from ground penetrating radar(GPR) images and the grain size characteristics of Dongshan(DS) profile of Chanle,along with the comparison of sedimentary structure and grain size between Donghai(DH) and DS,we initially identified the development order and chronology of the DS dunes.Through a comprehensive correlation of the series of sea level variation in Fujian,northern hemisphere temperature change,and East Asian monsoon in the same period,we discussed the development of Changle coastal dunes and its environmental significance and finally drew the following preliminary conclusions:(1)The profile outcrops, along with GPR images,showed that the DS and DH dunes are mostly made of landward stratification,indicating the sands mainly transmit landward.The dunes stratifications include plate-type cross-bedding,wedge-shaped cross-bedding,horizontal bedding,etc.Compared with the inland desert dunes,coastal dunes’ structures here tend to be simpler,and are always consistent with the local prevailing NNE and NE wind.(2)Grain size analysis demonstrated that,particle size composition of DS and DH are mainly similar to the coastal dunes in other regions of China,with a large amount of medium and fine sand and their total contents about 80.75～87.52%.The samples collected in the bottom 7m section of DS profile are averagely coarse,bad sorting,negative skewness and sharp kurtosis.These grain size parameter characteristics are close to those of the beach sand,showing that the early development of dune is controlled by the wind and waves.The upper 7m section of DS and the entire DH show typical coastal aeolian dune characteristics.(3)According to the OSL dating data of dune,AMS14C chronology,the results of environmental archaeology,and the historical coast change map,we preliminary reconstructed the chronology of the dune development.The DS dune developed since 6kaB.P..The transformation from neritic faces to beach faces occurred in the period ranging from 5.6 to 1.7kaB.P..Between 1.7 and 0.8kaB.P.,dune growth was interrupted. Aeolian dunes started to form since 0.8kaB.P..Both DS’s sensitive grain size and DH mean grain size indicated gradually increasing winter monsoon in the period of dunes development.In the little ice age,sandstorm activities were so intense that coastal dunes extensively developed.(4)The coastal dunes in Changle of Fujian developed in the Holocene with relatively high sea level.Under the circumstance of various dry events and intense winter monsoons in the middle and late Holocene,the sea level slightly regressed after the maximum height,resulting in the widespread coastal dunes development.That is,the development of coastal dunes in the study area,experienced sea level rise and fall in the middle and late Holocene.Dunes mainly formed in the period during which sea level declined slightly since 6kaB.P..The late Holoence dry and cold climate and increasing winter monsoon intensity are important factors controlling the coastal aeolian dunes’ development.For dunes developing in the intertidal zone,early wave and tide also played an important role.