Coastal Environment Evolution Along The Western Taiwan Strait In Late Holocene:Recorded By Coastal Dunes

Aeolian sediment that has been characterized in many coastal zones along the Taiwan Strait,Southeastern China,might record the history of coastal aeolian activity that goes back thousands of years and provide information about regional sea level changes and fluctuations of the East Asian Winter Monsoon(EAWM).In this study,field survey,grain size measurement and systemic optically stimulated luminescence(OSL)dating were applied to several coastal dune profiles along the western Taiwan Strait.In order to understand the formation and reactivation history of coastal dunes on a larger scale,estimated luminescence results were compared to other published luminescence results of the coastal dunes on both side of the Taiwan Strait.Based on the OSL chronology framework of regional coastal dunes,we discussed the evolution of coastal environments,and the drive mechanism.Results show that:(1)According to field survey,we found that the coastal aeolian sediment in study area is characterized by horizontal bedding,oblique bedding,wave bedding,and local cross bedding.All the aeolian sediments have inherited the characteristics of regional parent rock,mainly quartz,followed by feldspar,and a small amount of dark minerals,like biotite and hornblende.(2)The coastal dune sand samples are dominated by medium to fine sand,and with a few certain component of coarse sand,a small amount of other grain size components.The results of grain size analysis and the sediment structural characteristics showed that most of the costal dunes we studied are typical aeolian sediments.In addition,the lower section of the SDA profile might be the beach deposit under the control of wave and tide,and then was affected by wind.(3)The OSL dating results showed that the coastal aeolian sediment of the study area were formed since 4.4 ka,i.e.,since the late Holocene.Based on the new OSL data of coastal dune profiles we provided and the other published luminescence results of the coastal dunes on both side of the Taiwan Strait,we combined all the sediment characters of dune profiles,like bedding structures,unconformity,paleosoil layer and the grain size parameters,to establish the OSL chronology framework of regional coastal dunes development history.Several periods of dune development and aeolian activity have taken place in the study area since the late Holocene.They are-4.4 ka,3.6-3 ka,2.8-2.3 ka,2-1.1 ka,and 0.9 ka-present,respectively.(5)By comparing these OSL records with other paleoenvironment and paleoclimate proxies,we believe that the development of regional coastal dunes occurred during periods of lower sea level or when the sea level had reached the present position.At the same time,coldarid climate with an enhanced winter monsoon is more conducive to the development of coastal dunes.During the Little Ice Age(LIA),the EAWM was quite strong,the coastal aeolian activity on both sides of the Taiwan Strait,the northeastern coast in China,the coasts of Japan and Korea were quite consist,which shows that the EAWM was the basic driving force of coastal aeolian activities.(6)The comparison of the coastal aeolian sediment records between the east and west sides of the Eurasian Continent shows that,on the century-scale,the coastal aeolian activities in our study area and the North Atlantic Oscillation(NAO)might have the inverse phase relation.During the LIA,the climate and the coastal environment of the North Hemisphere were deteriorated.Under these situations,continued aeolian activities and aeolian deposition occurred on the sandy coasts of both sides of the Eurasian Continent.(7)In the Southeast coast zone of China,with a dense population,the influence of social,economic and cultural activities on coastal aeolian activity and dune formation could not be ignored.Since the Ming and Qing Dynasties,especially in recent decades,the natural evolution process of coastal dune in the study area has been greatly influenced by human activities.Therefore,in the related research,the interference effect of man-induced factors on coastal aeolian activity and dune formation must be taken into account.