长江口表层沉积物矿物磁性分区特征及其沉积环境指示意义

摘要

This study attempted to reveal the distribution patterns of magnetic minerals in the various sedimentary environments of Changjiang River mouth and adjacent continental shelf,and assessed proxies of magnetic parame-ters for identifying sedimentary environments,and the obtained results would be used to better perform the paleo-environmental reconstruction.We collected surficial sediments from the following six sedimentary environments at the Changjiang River mouth and adjacent continental shelf:distributary channel,river mouth shoal,delta front slope,prodelta,transitional regions and relict sand,and measured their grain size and magnetic properties.The re-sults showed that,significantly highχ and SIRM values were obtained for sediments from the distributary channel and river mouth shoal,and high values of HIRM,χfd%,χARM ,χARM/χandχARM/SIRM were measured for sediments from prodelta and delta front slope,indicating that the distribution of magnetic minerals was controlled by the dis-persal of terrigenous sediments and hydrodynamic sorting.We proposed that for the Holocene stratigraphy,mag-netic parameter assemblage of HIRM,χARM ,χARM/χ andχARM/SIRM could be the effective indicator for identifying prodelta and delta front slope,andχ、SIRM and S -20mT can be used to recognize the distributary channel and river mouth shoal.%本研究旨在揭示现代长江口不同沉积环境铁磁性矿物的分布差异，寻找有效识别河口－陆架沉积环境的磁学指标，以便更好地将环境磁学应用于河口古环境研究。在长江口及邻近陆架的6个沉积环境：汊道、拦门沙、三角洲前缘斜坡、前三角洲、前三角洲－陆架过渡区和残留砂区，采集表层沉积物样品，进行粒度和磁性测量。结果显示，χ和 SIRM 在汊道和拦门沙呈现显著高值，HIRM、χfd％、χARM、χARM／χ和χARM／SIRM 在前三角洲和前缘斜坡呈现显著高值，反映了陆源物质输运距离和河口沉积动力对磁性矿物分布的控制作用。因此，参数组合 HIRM、χARM、χARM／χ和χARM／SIRM 可用于识别全新世地层前缘斜坡和前三角洲－陆架；参数组合χ、SIRM 和 S－20mT 可尝试用于识别汊道和拦门沙环境。