辐射沙脊群西洋潮流通道的浅部沉积层序及其形成演化

Since the late Quaternary, both the Yellow River and Changjiang River entered into the South Yellow Sea flowing through the middle Jiangsu coast. As a result, a series of sediments have been deposited in this area controlled by the river-sea interactions. The Radial Sand Ridge Field (RSRF) off the middle Jiangsu coast has been formed after the Holocene transgression. The Xiyang tidal channel in the northwestern RSRF is constrained by the tidal flat coast and tidal ridges. It is located in the transition zone between the northern Abandoned Yellow River delta and southern modern Changjiang River delta. Therefore, it becomes the important window area to reveal the sedimentary sequence formed in the coast and continental shelf under the active interactions between different large rivers during the late Quaternary. So far, the concerned studies are still limited. As to the upper strata with the depth less than 50 m below the current mean sea-level in the Xiyang tidal channel, there are still different viewpoints on its sedimentary sequence, chronology framework and evolution. Thus, this project selects the Xiyang tidal channel as the study area. Based on the 3D visualization of the seismic sequence framework, the spatial characteristics of the seismic units and main reflection interfaces would be extracted. Furthermore, combined with the sedimentology and chronology studies of the designed cores, the reliable chronology framework would be set up expectedly, and the provenance from large rivers would be identified. Applying the sequence stratigraphy method, referencing the adjacent published core data, it is targeted to ascertain the shallow sedimentary sequence in the Xiyang tidal channel, and to reveal its evolution. It would be of great significance to improve the understanding of sedimentary products under the interactions between large rivers in the coast and continental shelf area, to reveal the material basis and evolution of the scoured tidal channels formed in the accumulated continental shelves. It would be helpful to promote the knowledge of evolution of the RSRF as well.

晚第四纪以来，黄河、长江都曾经江苏中部海岸注入南黄海，河海交互作用形成一系列沉积，全新世海侵后发育岸外辐射沙脊群。沙脊群西北部、由岸滩与沙脊所夹持的西洋潮流通道，位于北侧废黄河三角洲和南侧长江三角洲两大地貌单元间的过渡区，成为揭示不同大河交互作用下的海岸、陆架晚第四纪沉积层序模式的重要窗口，目前对其标高-50 m以内浅部沉积层序、年代及形成演化的有限研究尚存在不同认识。本项目以西洋潮流通道为研究区，基于层序地层学方法，通过对已有浅层地震剖面进行地震层序格架的三维可视化、提取地震单元和反射界面的空间分布特征，结合控制性钻孔的沉积学和年代学研究，构建可靠年代框架、判识大河物源，并参考邻区钻孔资料，来探明西洋潮流通道的浅部沉积层序、反演其形成演化。该研究成果对于丰富认识大河与海岸、陆架交互作用的产物，揭示堆积型陆架的冲刷型潮流通道的物质基础与形成演化，提升对辐射沙脊群形成演化的认识具有重要意义。

晚第四纪以来，黄河、长江都曾经江苏中部海岸注入南黄海，河海交互作用形成一系列沉积，全新世海侵后发育岸外辐射沙脊群。沙脊群西北部、由岸滩与沙脊所夹持的西洋潮流通道，位于北侧废黄河三角洲和南侧长江三角洲两大地貌单元间的过渡区，成为揭示不同大河交互作用下的海岸、陆架晚第四纪沉积层序模式的重要窗口，目前对其标高-60 m以内浅部沉积层序、年代及形成演化的有限研究尚存在不同认识。在完成西洋浅部地震层序格架、控制性钻孔的沉积序列和年代框架以及可能与古黄河有关层位的物源示踪等研究内容的基础上，再结合搜集整理的邻区钻孔资料，我们获得以下主要认识：（1）西洋地区标高-60 m以内的浅部沉积形成于MIS 7晚期以来，先后保存了MIS 7晚期较高海面、较强水动力的潮汐河口（边滩、河床），MIS 6-5时期冷干转为暖湿、海面先下降后上升和较弱水动力的淡水与滨岸湖沼，MIS 5时期较高海面、较强水动力的潮汐河口三角洲（三角洲前缘、前三角洲等），MIS 1时期较高海面、较强水动力的水下沙脊-潮道等环境的沉积记录；该区普遍缺失MIS 4-2时期的陆相沉积，可能被冰后期海侵和现代强劲潮流动力冲刷殆尽所致；表层全新世沉积（大致对应于浅层地震单元U1）厚度在水下沙脊处基本不足10 m，其余普遍不足5 m，甚至缺失。（2）MIS 7晚期以来西洋地区沉积可能一度受到过古长江物源的影响，但钻孔黏土矿物组合特征清晰地指示了该区受到古黄河物源影响更为持久，尤其是MIS 5时期发育了古黄河三角洲沉积体系（远端和近端三角洲前缘等）。（3）西洋西北段和东南段的地震层序存在一致性差异，主要表现为浅层地震单元U3仅在西北段稳定分布，向南厚度减薄、直至33°19′N附近尖灭；这一特征表明MIS 5时期古黄河三角洲前缘的泥质远端部分（或前三角洲）沉积记录局限于西洋西北段，东南段仅发育砂质近端部分或泥质远端部分已被侵蚀掉。