黄海北部全新世泥质沉积体的沉积通量与层序演化

The Holocene mud deposit system in northern Yellow Sea is a fine sediment body which stretches from the west of North Yellow Sea to the center of South Yellow Sea, extending along the northern bank and eastern tip of Shandong Province. A major part of the mud deposit located on the east and south of Shandong Province will be researched in this study. According to interpretation of the high-resolution sub-bottom profiles, analysis of date, grain-size, density and micropaleontology of the sedimentary cores, and synthesizing sea-level change of the Yellow Sea, sediment discharge of the Yellow River and strata thickness of the mud body, this proposal is intended to establish the fine stratigraphic structure and spatial distribution pattern of the Holocene mud deposit system in the northern Yellow Sea, to recognize the changes of stratigraphic structure and sedimentary pattern of the mud deposit which extends from the offshore wedge-like “Shandong Province subaqueous delta” to the shelf patch-like “central South Yellow Sea mud area”, to study the sequence development of the mud deposit as a whole sedimentary system, to estimate the volume and sediment flux of the mud body and its strata units, to reveal the response relationship between sediment flux change of the mud deposit and sea-level change of the Yellow Sea in the mud’s developmental process, to explore the impact of changed sediment discharge and channel migration of the Yellow River on the development of the mud deposit. This project is significant to explain the formation mechanism of shelf mud deposit and the source-to-sink process of river sediment dispersal system.

黄海北部全新世泥质沉积体是指从北黄海西部起沿山东半岛北岸绕过成山头向南延伸到南黄海中部的细颗粒沉积体。本申请拟以该沉积体在山东半岛以东和以南的部分为研究对象，通过高分辨率浅地层剖面解释和沉积物岩心的年代、粒度、密度、微体古生物分析，并收集综合黄海海平面变化、黄河历史入海泥沙通量变化和地层厚度等资料，建立黄海北部全新世泥质沉积体的精细地层结构和时空分布格局，认识沉积体由近岸区楔形“山东半岛水下三角洲”延伸为陆架区平缓斑块状“南黄海中部泥质区”层序结构和沉积方式的变化，将该沉积体系作为统一的整体研究其层序演化模式，并估算沉积体各地层单元的体积和沉积通量，揭示沉积体各演化阶段沉积通量变化对海平面波动的响应关系，探讨黄河入海泥沙通量变化和黄河改道对沉积体沉积过程的影响。本课题对于研究陆架泥质沉积体的形成机制和河流入海沉积物扩散体系的源–汇过程有重要意义。

陆架泥质沉积保存了丰富的环境信息，是研究全球变化的重要材料。黄河入海泥沙在海洋动力作用下形成了沿山东半岛北岸向东绕过成山头向南延伸的黄海北部泥质沉积体。作为重要研究材料，对该沉积体地层结构、空间分布、沉积通量、形成演化等问题的认识尚不充分。针对这些问题，本项目重点选择该沉积体在山东半岛东端的部分开展工作。文献综述从宏观上认识了末次冰消期以来黄海不同沉积体系的分布格局与演化过程。浅地层剖面解释和钻孔分析将该沉积体的地层结构分为三层。下层U3形成于11.2–9.6 ka，底界是mwp-1b形成的海侵面；中层U2形成于9.2–7 ka，底界是mwp-1c形成的海侵面；上层U1形成于7 ka以来，底界是最大海泛面。地层追踪发现北黄海和南黄海中部的斑块状泥质区是该沉积体向海的延伸。层序内部反射特征表明，U3是向海单向倾斜的斜坡沉积，U2和U1是向海、向陆双向倾斜的“Ω”形沉积，前积层角度达0.5°，从近岸泥质楔过渡为陆架泥质区沉积方式由侧向进积转变为垂向加积。地震剖面时深转换获取的地层厚度表明：该沉积体的沉积中心围绕山东半岛东端分布，最厚部位在山东半岛东南部，达45 m以上；U3和U2的沉积中心位于山东半岛北部和东部，最厚20 m以上；U1的沉积中心位于山东半岛东南部，最厚25 m以上；上覆地层沉积中心位置相对下伏地层向海扩展。根据地层厚度和岩芯分析获得的沉积物密度，计算得出测线控制范围内该沉积体的质量为470 Gt，其中，U1层270 Gt、U2层115 Gt、U3层85 Gt。根据测线控制范围占整个沉积体的比例，估算11.2–7 ka之间该沉积体的沉积通量为0.1 Gt/a，大致相当于该时期的黄河入海泥沙通量，但7 ka以来该沉积体与黄河入海泥沙的收支情况有较大差异。粘土矿物物源判别发现，该沉积体的沉积物组成与黄河最接近。海平面上升增大可容纳空间，沿岸流输运沉积物，海洋锋阻隔悬浮体向外扩散并有利于其沉降，是控制该沉积体形成与演化的主要因素。本项目研究成果对于认识河流入海沉积物在陆架区扩散沉积的“源–汇”过程有重要科学意义。