东海北部舟山群岛第四纪海陆交互沉积的磁性地层学研究及其古环境意义

Sedimentary system in marginal seas is not only a sink of terrestrial materials but a source of deep-sea deposition. It plays a crucial role in global sediment flux, ocean chemical flux and paleoenvironmental changes. The East China Sea was formed during the Cenozoic, with thick sediments of fluvial, lacustrine and marine deposited in this critical area. These sediments are widely employed for environmental and geological research, including the history of marginal-sea and shelf evolution, monsoon climate, and land-sea interaction. However, long-core studies were insufficient in reconstructing regional environments during the Quaternary, and most of these cores were located in the Changjiang River Delta. Herein, three new cores drilled from the northern East China Sea will be studied. Firstly, rock magnetism of boreholes and marine surface samples will be studied to detect the types, contents and grain-size of magnetic materials and the differences between these samples. After demagnetizing boreholes’ samples and obtaining their primary remanence, the result will be correlated with rock magnetism and with regional stratigraphy, and the time framework of three boreholes will be established. Finally, the accurate timing of each important event will be reconciled with regional and global changes to detect the relationship between them. This study will provide new insights of Quaternary evolution and paleoenrivonmental changes of the northern shelves of China.

边缘海的沉积体系，是陆源物质的“汇”，又是远洋沉积的“源”，在全球的沉积通量、海洋化学通量、古环境演化等方面均具有重要地位。东海地区的巨厚新生代沉积在研究边缘海演化、区域环境历史、海陆交互作用等重要科学问题中受到了广泛关注。然而，较长沉积序列的磁性地层学研究相对较少，多集中在现代长江三角洲地区，且不同地点、构造单元上的钻孔结果存在较大差异。针对这一现状，本项目拟利用在东海北部海域新近获取的具有代表性的三支钻孔，通过以磁极性地层学为主，结合岩石磁学等多种磁学参数，并综合东海地区相关的岩石地层学、生物地层学等资料来对地层进行划分和对比，构建东海北部第四纪沉积的磁性地层和年代框架，为区域环境过程提供更深入的素材。同时探讨主要地质事件发生的精确时间及其与全球变化之间的联系，有望在我国北方陆架第四纪演化研究上取得重要进展。

边缘海的沉积体系，是陆源物质的“汇”，又是远洋沉积的“源”，在全球的沉积通量、海洋化学通量、古环境演化等方面均具有重要地位。东海地区的巨厚新生代沉积在研究边缘海演化、区域环境历史、海陆交互作用等重要科学问题中受到了广泛关注。本项目通过东海及其陆架区多支钻孔的地层年代学、沉积动力、古环境研究，结合区域已有的研究成果，探讨了区域环境过程的演化特征及其影响机制，获得如下几点认识：（1）大多数沉积物中所包含的磁性矿物为低矫顽力的磁铁矿，同时含有少量的赤铁矿或针铁矿成分，这些钻孔沉积物可能均属于中、晚更新世-全新世；（2）中全新世以来与黄海暖流有关的长江入海物质主导了南黄海中部泥质区沉积物磁性性质；（3）重建了早全新世热带气旋的强度变化，发现其与太阳活动、季风强度和厄尔尼诺—南方涛动的变化有较好一致性；（4）发现东亚夏季风变率和黄海暖流的相关关系呈现显著的变化特征，揭示北极涛动通过影响黑潮、ENSO等关键环境因子进而控制晚全新世夏季风与陆架海流耦合。这些新认识加深了对东部陆架地区古环境演化的理解，为后续开展晚第四纪-全新世的高分辨率海陆环境过程对比奠定了基础。