莱州湾南部晚新生代海-陆相沉积的磁性地层学研究

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 Bohai Sea in China was formed by subsidence during the Cenozoic. Some 2000-3000 m of fluvial, lacustrine and marine sediments has been deposited in the basin. These sediments are widely employed for environmental and geological research, including the history of shelf evolution, monsoon climate, and the environmental impact on ancient human activities. However, long-core studies were insufficient in reconstructing regional environments during the Cenozoic era. However, most of these cores were located in the coastal plaints of the northern China, where tectonic activities were complicated, causing difficulties in reconciling there studies. Herein, a new core, BH1 borehole, located the south Bohai Sea will be studied. Firstly, rock magnetism of borehole 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 borehole samples and obtaining their primary remanence, it will be correlated with rock magnetism and with regional stratigraphy, and the time framework of the borehole will be formed. 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 paleoenrivonmental changes 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。渤海地区的巨厚新生代沉积在研究区域环境历史、海陆交互作用和人类活动等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，多集中在华北的滨海平原区，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，本项目拟利用在渤海南部海域新近获取的具有代表性的BH1钻孔，通过以磁极性地层学为主，综合岩石磁学等多种磁学参数，并结合渤海地区相关的岩石地层学、生物地层学、气候地层学等资料来对地层进行划分和对比，构建渤海南部晚新生代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研究素材。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，有望在晚新生代以来的北方陆架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。渤海地区的巨厚新生代沉积在研究区域环境历史、海陆交互作用和人类活动等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，多集中在华北的滨海平原区，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，本项目利用在渤海南部海域新近获取的多支钻孔，通过以磁极性地层学为主，综合岩石磁学等多种磁学参数，并结合渤海地区相关的岩石地层学、生物地层学、气候地层学等资料来对地层进行划分和对比，在构建渤海南部晚新生代沉积的磁性地层和年代框架的基础上，首次实现了环渤海地区上新世以来盆地尺度的地层对比，提出了渤海盆地陆-海转换的三阶段的概念模式：~3.7 Ma之前，盆地快速沉降，表现为河流、冲洪积相堆积为主；3.7-0.3 Ma，盆地沉降较为稳定，表现为“渤海古湖”发育，庙岛古隆起相对地势较高；~0.3 Ma以来，伴随着庙岛古隆起的解体，“渤海古湖”消失，渤海陆架开始形成。此外，通过不同季风材料的统计对比，在渤海海侵沉积研究的技术上，提出了季风轨道尺度变率的原创性假说：岁差周期主导的季风轨道尺度变率可能来自季风降水中的大-暴雨（台风降水）；100ka周期主导的黄土磁化率则可能反映了季风降水中的有效降水的信息。这些研究成果，为了解海陆变迁的机制与过程、海陆气候变化的相互影响、东亚环境过程在全球变化中的可能地位提供了更为详尽的资料与新的视角。