福建东南沿海海岸沙丘记录的风沙环境演变

Coastal sand dunes is a common aeolian landform in the sandy coast, which record the evolution process of aeolian landform power system，and also reflect the complex interaction among land surface, atmosphere and ocean. Therefore, coastal dune fields is the sensitive area of global climate change. However,progress on the evolution process of coastal sand dunes is hamperared by a lack of absolute dating data of sand deposits, and more previous results focus on the cause of coastal dunes formation over the past twenty years in China.In recent years, the development of optically stimulated luminescence (OSL) dating provide an effective technical method for sand deposit dating, and a more accurate reconstruction study of coastal sand dunes evolution process can be made to work. The sandy coast distributed in the southeast coast of Fujian Province offers a good opportunity for us carrying out the goal of the study. For this, the research project will select several typical coastal sand dunes and coastal aeolian deposits (old red sand) profile with high resolution sampling for the coastal aeolian environmental reconstruction study. The chronology of coastal sand dunes evolution will be based on OSL dating of aeolian sand deposits and Accelerator Mass Spectrometry radiocarbon dating (AMS14C) of palaeosols, complemented with sedimentary structure sequence analyses by artificial trial trench, ground-penetrating radar (GPR) profile. On this chronology framework, we will place sand particle size parameters as the primary proxy,which has an explicit aeolian physical meanings, and analyz synthetically other environmental proxies such as susceptibilities and element geochemistry characteristics of coastal sand deposits, to reconstruct the sequence of coastal sand dune development and aeolian environmental evolution in differing time scales. By comparing with the typical sedimentary sequence of coastal sand dunes in the southeast coast of Australia, we will further discuss the possible effects of global and regional climate environment events, such as changes of solar radiation and sea-level, on the evolution process of coastal sand dunes.

海岸沙丘是砂质海岸带常见的风沙地貌类型之一，记录了海岸带风沙动力地貌系统的演变过程，也反映了陆地、大气和海洋之间的复杂相互作用，在全球变化研究中具有重要意义。本项目以福建东南沿海的海岸沙丘和海岸风沙沉积为研究对象，采用OSL测年技术对海岸风沙进行测年，结合有机质AMS14C测年校验，辅助人工探槽、GPR探测技术观测海岸沙丘沉积构造，确定独立的海岸沙丘年代学标尺和海岸风沙沉积年代学框架；在系统的剖面年代标尺基础上，通过高密度采样进行各个环境代用指标的实验分析，并以物理意义明确的粒度参数作为主要代用指标，结合环境磁学、地球化学元素等辅助代用指标的综合分析，重建研究区不同时间尺度上海岸沙丘记录的风沙环境演变序列。通过南北半球海岸沙丘发育序列年代学的直接对比，探讨全球和区域气候环境事件对海岸风沙演变过程的可能影响。

福建东南沿海分布的古风成砂（老红砂）和海岸沙丘是“陆-海-气”耦合作用的产物，在提取第四纪气候-海平面演变序列和历史时期海岸风沙活动信息方面具有重要价值。本项目研究福建东南沿海古风砂（老红砂）记录的第四纪气候-海平面变化模式，研究海岸沙丘记录的近两千年来海岸风沙活动的总体特征。项目实施以来有以下新发现：.（1）通过多个剖面ESR、OSL年代和沉积序列综合分析，发现老红砂最老年龄可达1MaBP左右，而最新年龄仅1KaBP左右。第四纪中更新世以来，福建东南沿海老红砂发育可划分为多个沉积-红化阶段，其中MIS5以来的沉积-红化阶段就多达5-6期以上。.（2）福建东南沿海的老红砂，是第四纪中更新世以来高海面时期沉积的海岸古风砂层，在干湿交替的亚热带气候条件下发生红化作用形成的。其中，中更新世老红砂埋藏于连岛沙坝灰绿色海侵夹层之间，而MIS5以来的老红砂层构成高于现代海平面的侵蚀残留台地。.（3）在MIS5-MIS3阶段发育的老红砂台地剖面上，具有明显的棕红色-黄橙色的旋回沉积分层特点，各层色度、粒度和磁化率等参数有显著的峰谷值波动变化，可能记录了亚热带气候带在福建东部沿海发生过大尺度的南北摆动迁移。.（4）通过多个典型海岸沙丘剖面30余个样品进行OSL测年，结合AMS14C年代、海岸线变迁历史考古年代校验以及海岸地貌的系统分析，表明福建东南砂质海岸带尚存的多列海岸沙丘，主要是最近2000年以来尤其是在小冰期海退时期形成发育的。.（5）基于探地雷达（GPR）获得海岸沙丘沉积序列，以OSL测年为主，参考AMS14C年代、海岸环境考古年代校验建立的年代标尺综合分析，表明近两千年来福建砂质海岸带至少发生过3-4个风沙活跃期。 .上述研究成果表明，第四纪全球气候-海平面变迁对福建砂质海岸的风砂沉积-风化过程产生了深刻影响。东亚冬季风的波动增强，可能是近两千年来阶段性驱动海岸风沙活动的主要因素之一。