Coastal Dune Development Process And Its Environmental Significance Based On The OSL Dating,Jinjiang Of Fujian

The coastal sand widely distributed in southeast coastal of China is the product of the coastal environment evolution. Grain size characteristics of the coastal sand and their chronology potentially can greatly improve the interpretation of past environmental changes and provide valuable information on the past aeolian activity. However, lacking of direct dating methods, domestic scholars mainly fouce on the distribution, grain size characteristics and geomophogensis to the coastal sand research, including the "Old RedSand" named in china, a kind of paleocoastal sand, and the modern coastal sand. In this paper, Quartz single aliquot regenerative optically-stimulated luminescence(OSL) dating with high resolution sampling was applied to coastal sand in China for the KR"Old Red Sand"sectionand the Anshan(SHA) section nearby the Anshan Archaeological site,in the Jingjiang coast, southeast Fujian. Then OSL dating was employed to establish thechronology of two section. Based on OSL ages, sedimentology and proxy data(grain size), and compared withglobal sea-level change, East Asian monsoon change sequence,history of typhoon landfalls in Fujian,the we conclude that:(1) The result of grain-size analysis shows that, the two section are also can be divided into two layers, the upper12.5m and3.1m of the KR section and SHA section demonstrate a typical coastal aeolian sand characteristics, and the under layer for a coastal beach ridge, the formation of which is not only affected by the aeolian transport,but also by the wave.(2) The OSL age of the26samples range from125ka to12ka shows that KR "Old Red Sand" has existed since the last interglacial, six period of costal aeolian sand activity can be division, respectively in125-115ka、105-97ka、84-74ka、61.5-52ka、39-29ka、15-9ka, and the OSL age shows that the "Old Red Sand"deposition existed five obvious hiatus. These reveal that the KR "Old Red Sand"deposition mainly occurred in relation to the sea-level highstands, but lower sea-level of Last Glacial Maximum(LGM) have nondeposition. May be affected by the strong winter monsoon, which bring beach sand to coastal area deposition, so "Old Red Sand"deposition also occurred during the secondary low sea-level in the high sea-level period. According to the depth variation of the Taiwan Strait, and global sea-level change sequence, it would appear that a sea level of c.-70m relative to the present was the threshold for the coastal Aeolian sand activation and "Old Red Sand"deposition. When the sea level lower than c.-70m, coastal aeolian sand activation is restricted due to longer sediment transport distances and decreased sediment supply; When the sea-level higher than c.-15m, coastal aeolian sand and the "Old Red Sand"deposition under strong or weak winter monsoon all can form, but mainly formed at times of a descent stage in the sea-level highstands. When the sea-level lower than c.-15m higher and than c.-70m, the coastal aeolian sand deposition of the study area must have a powerful winter monsoon.(3) The OSL age of the11samples range from839±132a to108±21a shows that SHA section formed in nearly1000years, three period of costal aeolian sand activity can be division, respectively in AD1050-1300, AD1470-1600, AD1720-1950, especially during the little ice age (LIA), costal aeolian sand activity strong, the development of coastal dunes sand is prevailing, and the OSL age shows that the coastal aeolian sand deposition represent a multiphase and episodicfeature. We discussthe main controls of coastal aeolian sand development in research area based on the OSL chronology and compare to East Asian monsoon change sequence and the history of typhoon landfallsin Fujian, the result shows that the main control is the intensive of East Asian winter monsoon, but not the precipitation,typhoon landfalls and sea level change,the phase of Aeolian activity main correspond to an stronger East Asian winter monsoon period,but over the last half-century, the weakened aeolian activity may link to human activities on a large number of mining sand beside a weakened winter monsoon.