北黄海中部晚第四纪以来古河道的物源演变及其对海平面变化的响应

There exists multi-stage paleo-channels formed in the sea-level lowstand period since the Late Quaternary (MIS 6) in the central North Yellow Sea (NYS), which carries abundant information on the sea-level changes and environmental evolution in NYS. In this project, throuth a comparison between sedimentary characteristics of the paleo-channels recorded in the core DLC70-2 with the longest length and highest recovery rate by far, and core-passing subbottom seismic profile in NYS, the stratigraphic boundaries of the paleo-channels in different stages will be determined. Based on the Chronology of AMS C-14 and Optically Stimulated Luminescence (OSL) dating, the time series of paleo-channels in the central NYS since the Late Quaternary will be precisely disclosed. In addition, by a systematic geochemical analysis of rare earth element (REE) and Sr-Nd isotope from the sediments (<32µm fractions)of core DLC70-2, the discrimination indicators for tracing the sediment sources of paleo-channels will be extracted, which will be compared with the same grain-size fractions from the major rivers(the Yellow River, the Yangtze River,Liaodong Peninsula Rivers,Korean Rivers) around NYS. By this means, the provenance of paleo-channels in different stages in NYS will be fixed, and their responses to the global sea-level fluctuations since the Late Quaternary will be revealed. This study not only contributes to deeply understanding the geological evolutionary history in the shelf area of the eastern China Seas and enriching the regional response theory to global change, but also provides scientific evidences for summarine engineering construction in the study area.

北黄海中部晚第四纪（MIS6期）以来低海面时期发育多期埋藏古河道，是海平面变化和环境演化信息的重要载体。本申请拟通过北黄海中部目前最深和取芯最完整的DLC70-2孔记录的古河道沉积特征与过孔浅地层剖面记录的对比，确定不同阶段古河道的地层界面；结合AMS C-14和光释光测年资料，准确厘定古河道的时间序列；对该钻孔<32µm的沉积物组分进行稀土元素（REE）与Sr-Nd同位素地球化学的系统分析，提取不同阶段古河道的物源信息，并与周边主要入海河流（黄河、长江、辽东半岛河流、朝鲜半岛河流）相同粒级组分的鉴别指标对比，确立不同阶段古河道的物源属性，阐明北黄海中部晚第四纪以来古河道的物源演变对全球海平面变化的响应。本项研究有助于深入认识晚第四纪以来中国东部陆架的地质演化史，丰富全球变化区域响应的认识，并为该区的海底工程施工等人类活动提供科学依据。

北黄海中部陆架低海面时期发育埋藏古河道，保存了丰富的环境信息，是研究海平面变化和环境演化的重要材料。本项目通过北黄海中部DLC70-2孔记录的古河道沉积特征与过孔浅地层剖面记录的对比分析，结合测年资料，系统研究了不同阶段古河道的时间序列、物源属性及其沉积演化等。研究表明，晚更新世末北黄海中部硬质粘土层的形成年龄介于12563~10330 cal yr BP之间，年代上与发生在12.9~11.6ka期间的末次冰消新仙女木气候回冷事件相吻合，与不同沉积环境中形成的北黄海泥炭层为同一时期的沉积，可作为新仙女木事件在北黄海陆架响应的一个重要证据；北黄海晚第四纪以来发育3次不同低海面时期的古河道系统：MIS6期晚期的河流与河道充填相沉积，MIS4期晚期（~72.5±7 ka BP以后）的河口相沉积，末次冰盛期至新仙女木事件期间（~14602 至10357 cal yr BP）的河口相至河流泛滥平原相沉积；MIS6期晚期的古河道系统与鸭绿江密切相关，这一时期黄河改道苏北平原入海，同时渤海海峡阻隔了渤海物质进入研究区，而MIS4期晚期与末次冰盛期以来的古河道系统与黄河相对应；北黄海晚第四纪以来不同阶段形成的古河道不但受海平面变化的控制，而且与渤海海峡地形密切相关。本项研究有助于深入认识晚第四纪以来中国东部陆架的地质演化史，丰富全球变化区域响应的认识，并为北黄海海底工程施工等人类活动提供科学依据。